Air movement and heat loss from sheep. III. Components of insulation in a controlled environment

The rate of sensible heat loss from a Clun Forest ewe was studied at several fleece depths in a temperature-controlled chamber. A simple resistance analogue was used to describe the heat flow from different body regions. Heat loss from the trunk depends largely on the mean fleece depth l. The fleece resistance was about 1.5 s cm-1 per centimetre depth. Heat transfer through the fleece was accounted for by molecular conduction, thermal radiation and free convection. The fleece conductivity -kb attributed to free convection depends on the mean temperature difference (-Tst---Tct) across the fleece according to the relation -kb = 8.0 (-Tst---Tct)0.53. Estimates of the sensible heat flux from the trunk at environmental temperatures, Ta, between 0 and 30 degrees C range from about 8 W (l = 7.0 cm, Ta = 30 degrees C) to about 160 W (l = 0.1 cm, Ta = 0 degrees C). In contrast, the sensible heat loss from the legs depends mainly on the local tissue resistance. For environmental temperatures between 0 and 30 degrees C, the calculated tissue resistance for this region of the body varied from about 8 to 1 s cm-1. The corresponding heat loss from the legs was between 10 and 20 W, compared with between 3 and 7 W from the head. The fastest heat loss from the legs occurred at an environmental temperature of about 12 degrees C. Although the proportion of the heat loss from the extremities depends on environmental temperature, the total heat loss (sensible or latent) was closely related to the mean skin temperature of the trunk.     

Air movement and heat loss from sheep. I. Boundary layer insulation of a model sheep, with and without fleece

A model sheep, made from metal cylinders and hemispheres, was heated electrically. Heat loss by forced convection in a wind tunnel was analysed in terms of the dependence of the Nusselt number (Nu) on Reynolds number (Re). For a bare trunk Nu = 0.095 Re0.684, but with fleece covering the trunk to a depth of 3.5 cm, Nu = 0.0112 Re0.875 when the mean radiative temperature of the the coat was taken as the surface temperature. Heat transfer by convection from the whole body, including legs, was described by Nu = 0.029 Re0.80. However, a bulk Nesselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s-1 because the relation between mean surface temperature, Nusselt number and convective heat flux is not unique.     

Animal coat color and radiative heat gain: A re-evaluation

Summary Thermal resistance and heat gain from simulated solar radiation were measured over a range of wind velocities in black and white pigeon plumages. Plumage thermal resistance averaged 39% (feathers depressed) or 16% (feathers erected) of that of an equivalent depth of still air. Feather erection increased plumage depth four-fold and increased plumage thermal resistance about 56%. At low wind speeds, black plumages acquired much greater radiative heat loads than did white plumages. However, associated with the greater penetration of radiation into light than dark plumages, the radiative heating of white plumages is affected less by convective cooling than is that of black plumages. Thus, the heat loads of black and white plumages converge as wind speed is increased. This effect is most prominent in erected plumages, where at wind speeds greater than 3 ms^–1 black plumages acquire lower radiative heat loads than do white plumages. These results suggest that animals with dark-colored coats may acquire lower heat loads under ecologically realistic conditions than those forms with light-colored coats. Thus, the dark coat colors of a number of desert species and the white coat color of polar forms may be thermally advantageous.These results are used to test a new general model that accounts for effects of radiation penetration into a fur or feather coat upon an animal's heat budget. Even using simplifying assumptions, this model's predictions closely match measured values for plumages with feathers depressed (the typical state). Predictions using simplifying assumptions are less accurate for erected plumages. However, the model closely predicts empirical data for erected white plumages if one assumption is obviated by additional measurements. Data are not sufficient to judge whether this is also the case for erected black plumages.List of Symbols A body surface area (m²) - a _L long-wave absorptivity of coat - a _s short-wave absorptivity of coat - d characteristic dimension (m) - E evaporative water loss (kg m^–2 s^–1) - h coat thermal conductance (W m^–2 °C^–1) - k convection constant (s^1/2 m^–1) - l coat thickness (m) - L _i long-wave irradiance at coat surface (W m^–2) - M metabolic heat production (W m^–2) - m body mass (kg) - P plumage mass (kg) - p probability per unit coat depth that a penetrating ray will strike a coat element (m^–1) - q(Z) radiation absorbed at level z (W m^–2) - R _abs radiation absorbed by animal (W m^–2) - r _e external resistance to convective and radiative heat transfer (s m^–1) - r _Ha boundary layer resistance to convective heat transfer (s m^–1) - r _Hb whole-body thermal resistance (s m^–1) - r _Hc coat (plumage) thermal resistance (s m^–1) - r _Ht tissue thermal resistance (s m^–1) - r _s apparent resistance to radiative heat transfer (s m^–1) - r(Z) thermal resistance from level z to coat surface (s m^–1) - S _i short-wave irradiance at coat surface (W m^–2) - S ^– radiant flux going toward skin surface (W m^–2) - S ⁺ radiant flux going away from skin surface (W m^–2) - T _a air temperature (°C) - T _b core body temperature (°C) - T _e equivalent black-body temperature (°C) - T _e air temperature plus temperature increment due to longwave radiation (°C) - u wind velocity (m s^–1) - V heat load on animal from short-wave radiation (W m^–2) - z depth within coat (m) - short-wave absorptivity of individual hairs or feather elements - emissivity - {ie211-1} - latent heat of vaporization of water (J kg^–1) - short-wave reflectivity of individual hairs or feather elements - {ie211-2} short-wave reflectivity of coat - {ie212-1} short-wave reflectivity of skin - c _p volumetric specific heat of air (J m^–3 °C^–1) - Stefan-Boltzmann constant (W m^–2 °K^–4) - short-wave transmissivity of individual hairs or feather elements - {ie212-2} short-wave transmissivity of coat     

Kinetics of the inhibition of human pancreatic elastase by recombinant eglin c. Influence of elastin.

Recombinant eglin c is a potent reversible inhibitor of human pancreatic elastase. At pH 7.4 and 25 degrees C, kass. = 7.3 x 10(5) M-1.s-1, kdiss. = 2.7 x 10(-4) s-1 and Ki = 3.7 x 10(-10) M. Stopped-flow kinetic indicate that the formation of the stable enzyme-inhibitor complex is not preceded by a fast pre-equilibrium complex or that the latter has a dissociation constant greater than 0.3 microM. The elastase-eglin c complex is much less stable at pH 5.0 and 25 degrees C, where kdiss. = 1.1 x 10(-2) s-1 and Ki = 7.3 x 10(-8) M. At pH 7.4 the activation energy for kass. is 43.9 kJ.mol-1 (10.5 kcal.mol-1). The kass. increases between pH 5.0 and 8.0 and remains essentially constant up to pH 9.0. This pH-dependence could not be described by a simple ionization curve. Both alpha 2-macroglobulin and alpha 1-proteinase inhibitor are able to dissociate the elastase-eglin c complex, as evidenced by measurement of the enzymic activity of alpha 2-macroglobulin-bound elastase or by polyacrylamide-gel electrophoresis of mixtures of alpha 1-proteinase inhibitor and elastase-eglin c complex. The rough estimate of kdiss. obtained with the alpha 2-macroglobulin dissociation experiment (1.6 x 10(-4) s-1) was of the same order of magnitude as the constant measured with the progress curve method. Eglin c strongly inhibits the solubilization of human aorta elastin by human pancreatic elastase. The extent of inhibition is the same whether elastase is added to a suspension of elastin and eglin c or whether elastase is preincubated with elastin for 3 min before addition of eglin c. However, the efficiency of the inhibitor sharply decreases if elastase is reacted with elastin for more prolonged periods.     

Convective and radiative components of wind chill in sheep: Estimation from meteorological records

Wind chill is defined as the excess of sensible heat loss over what would occur at zero wind speed with other conditions unchanged. Wind chill can be broken down into a part that is determined by air temperature and a radiative part that comprises wind-dependent effects on additional long-wave radiative exchange and on solar radiation (by reducing solar warming). Radiative exchange and gain from solar radiation are affected by changes that are produced by wind in both surface and fleece insulations. Coefficients are derived for (a) converting the components of sensible heat exchange (air-temperature-dependent including both convective and associated long-wave radiative, additional long-wave radiative and solar) into the components of the total heat loss that are associated with wind and (b) for calculating equivalent air temperature changes. The coefficients contain terms only in wind speed, wetting of the fleece and fleece depth; these determine the external insulation.Calculation from standard meteorological records, using Plymouth and Aberdeen in 1973 as examples, indicate that in April–September 1973 at Plymouth reduction in effective solar warming constituted 28% of the 24-h total wind chill, and 7% in the other months of the year combined; at Aberdeen the corresponding percentages were 25% and 6%. Mean hour-of-day estimates for the months of April and October showed that at midday reduction in solar warming due to wind rose to the order of half the air-temperature-dependent component of wind chill, with a much smaller effect in January. For about six hours at midday in July reduction in solar warming due to wind was similar in magnitude to the air-temperature-dependent component.It is concluded that realistic estimates of wind chill cannot be obtained unless the effect of solar radiation is taken into account. Failure to include solar radiation results not only in omitting solar warming but also in omitting the effects of wind in reducing that warming.The exchange of sensible (non-evaporative) heat loss between a homeothermic animal and its environment can be divided into two parts: one part is due to the temperature difference between the animal and the surrounding air, and the other part is due to additional long-wave radiative exchange between animal and environment and to solar radiation. Both parts of the heat exchange are determined in magnitude by the animal's thermal insulation, which is itself affected by windspeed and wetting. Wind diminishes as animal's external insulation, so increasing heat loss under all conditions when the air temperature is lower than the animal's surface temperature: this effect is termed wind chill. Wind chill has previously been investigated more commonly in relation to man (Burton an Edholm, 1955; Smithson and Baldwin, 1978; Mumford, 1979; Baldwin and Smithson, 1979). This paper is concerned with the separate contributions to wind chill calculated for sheep that can be associated with convective and radiative heat exchanges.     

The effects of thermoregulatory behaviour on the heat loss from shorn sheep as measured by a model ewe for micro-climate integration

A thermostatic, taxidermic model sheep was used to assess the effects of thermoregulatory behaviour of shorn sheep at night in a winter environment with mean air temperatures slightly above freezing, variable wind speeds, rain and cloud cover.Testing in a wind tunnel showed that angle of incidence to the wind had no effect on heat loss at wind speeds < 2 m s⁻¹ (7 km h⁻¹), but at wind speeds of 7 m s⁻¹ (25 km h⁻¹), heat loss was 14% greater when the model was side-on rather than tail- or head-on to the wind.In tests on pasture, standing side-on to the early morning sun reduced heat loss from the model by 33%. Three hours “lying” on the lee side of a 1-m high synthetic Sarlon windbreak on a frosty night resulted in a reduction in heat loss of 6% below that when standing or 11% below that in a standing position in the open. When the model was placed in the centre of a tight group of 16 shorn sheep, its heat loss was reduced by an average of 14%.Heat loss was also reduced if the model was moved from the open, to regions of lower wind speed adjacent to windbreaks; the effect was greater on the leeward than the windward side.The reduction one metre leeward of a grass hedge (hybrid Phalaris) was 15% compared with 12% one metre leeward of a synthetic (Sarlon) windbreak, which is consistent with the preference of shorn sheep to shelter by Phalaris rather than Sarlon windbreaks.The microclimates where heat loss from the model were lowest correspond to those sought by shorn sheep in cold weather, and the results indicate that shorn sheep have very sensitive thermosensing mechanisms and efficient thermoregulatory behaviour.     

Electrical resistance of muscle capillary endothelium.

A recently developed technique for in vivo determination of the electrical resistance of vascular endothelium in microvessels was applied to the vessels in a thin frog muscle, m. cutaneus pectoris. The technique consists of injection of current via a glass micropipette into a capillary and measurement of the resulting intra- and extravascular potential profiles with another micropipette placed at various distances from the current source. The theory of Peskoff and Eisenberg (1974) was used to handle the problems arising from distributed extravascular resistances and was experimentally shown to describe the external field satisfactorily. With this extension of one-dimensional cable theory the specific electrical resistance of arterial microvessels was 33 omega cm2 and of venous capillaries 23 omega cm2. The "length constants" were 135 and 112 micrometers, respectively. If results from arterial and venous vessels are taken together, the ionic permeabilities at 20 degrees C were PNa = 3.9 X 10(-5) cm X s-1, PK = 5.7 X 10(-5) cm X s-1, PCl = 5.9 X 10(-5) cm X s-1 and PHCO3 = 3.4 X 10(-5) cm X s-1. These figures agree with figures for capillary permeability obtained in tracer experiments on whole muscle. The study bridges a gap between single capillary and whole organ techniques with the conclusion that the two different approaches lead to similar results in muscle capillaries.     

中国南方典型地区油-稻轮作条件下大气SO2干沉降速率动态变化

以1998年11月～1999年10月中国科学院红壤生态试验站农田小气候观测站气象梯度资料(温度、风速、气压),计算近地面湍流特征参数(u^*、θ^*、L),然后采样阻力模式计算SO2干沉降速率(Vd)。研究了该地油-稻轮作条件下大气SO₂干沉降Vd动态变化．结果表明,一年中大气SO2干沉降Vd时平均年均值为0．124～0．897cm·s^-1(mean±SE=0．507±0．167cm·s^-1)．一年中大气SO2干沉降Vd存在如下规律性：白天>晚上．3～8月份SO2Vd平均值(0．611cm·s^-1)大于9～12、1～2月份SO2Vd平均值(0．401cm·s^-1)．水稻生长期间(0．605±0．093cm·s^-1)>油菜(0．491±0．166cm·s^-1)>休闲(0．342±0．174cm·s^-1)．     

Cushion size, surface roughness, and the control of water balance and carbon flux in the cushion moss Leucobryum glaucum (Leucobryaceae)

We explored the size dependence of water balance and carbon flux in the cushion moss Leucobryum glaucum (Leucobryaceae). Conductance to water vapor (g(a)) was modeled empirically using 4-24 cm diameter cushions (N = 14) evaluated across wind speeds from 0.7 to 4.3 m/s in a wind tunnel. Model parameters included wind speed (u), kinematic viscosity (v), cushion diameter (L(d)), and surface roughness (L(r)). The model g(a) = -9.62(u/v)(1.21) · L(d)(-0.35) · L(r-in)(-1.85) (where L(r-in) represents a dimensionless form of L(r); R(2) = 0.88) indicates negative relationships between g(a) and both L(d) and L(r). These predictions were evaluated during a 5-d field experiment where water loss and net carbon exchange (estimated by ΔF/F(m)') were monitored. In the field (N = 18, 4-34 cm diameter cushions), L(r), but not L(d), controlled rates of evaporation due to additional turbulence that reduced size dependence of cushions along the forest floor. However, the duration of positive net carbon gain varied from 1.4 to 4.4 d and was significantly longer in larger diameter cushions. Thus, under field conditions, size-dependent changes in surface-area-to-volume relationships influence the duration of net carbon gain more than differences in water flux and lead to a strong size dependence of water balance and carbon flux.     

Thermoregulatory responses to intermittent exercise are influenced by knit structure of underwear

The purpose of this study was to evaluate the role of knit structure in underwear on thermoregulatory responses. Underwear manufactured from 100% polypropylene fibres in five different knit structures (1-by-1 rib, fleece, fishnet, interlock, double-layer rib) was evaluated. All five underwear prototypes were tested as part of a prototype clothing system. Measured on a thermal manikin these clothing systems had total thermal resistances of 0.243, 0.268, 0.256, 0.248 and 0.250 m2.K.W-1, respectively (including a value for the thermal resistance of the ambient environment of 0.104 m2.K.W-1). Human testing was done on eight male subjects and took place at ambient temperature (Ta) = 5 degrees C, dew point temperature (Tdp) = -3.5 degrees C and air velocity (Va) = 0.32 m.s-1. The test comprised a repeated bout of 40-min cycle exercise (315 W.m-2; 52%, SD 4.9% maximal oxygen uptake) followed by 20 min of rest (62 W.m-2). The oxygen uptake, heart rate, oesophageal temperature, skin temperature, Ta, Tdp at the skin and in the ambient air, onset of sweating, evaporation rate, non-evaporated sweat accumulated in the clothing and total evaporative loss of mass were measured. Skin wettedness was calculated. The differences in knit structure of the underwear in the clothing systems resulted in significant differences in mean skin temperature, local and average skin wettedness, non-evaporated and evaporated sweat during the course of the intermittent exercise test. No differences were observed over this period in the core temperature measurements.     

Convective heat transfer measured directly with a heat flux sensor

A heat flux disk has been developed that directly measures the convective heat transfer in W/m2. When the sensor is calibrated on an aluminum cylinder, the calibration constant obtained is greatest in still air. As air movement increases, the calibration constant is reduced with increasing convective heat transfer coefficient, 0.5%.W-1.m2.K. The influence of wind on the calibration value is greatly reduced when the sensor is attached to a surface with lower thermal conductivity. The local convective heat transfer coefficient (hc) of the human body was measured. The leg acts in a manner similar to that of a cylinder, with the highest hc value at the front facing the wind and the lowest approximately 90 degrees from the wind, and in the wake a value is obtained that is close to the average hc value of the leg. When hc is measured at several angles and positions all over the body, the results indicate that the body acts approximately as a cylinder with a hc value related to the wind speed as hc = 8.6.v0.6 W.m-2.K-1, where v is velocity.     

The calculation from weather records of the requirement for clothing insulation

Standard meteorological measurements of dry bulb temperature, wind speed, sunshine, cloud cover and rainfall are used to calculate the clothing insulation required by man for thermal comfort under given weather conditions. The calculation is based on earlier work on the effect of weather on sensible (non-evaporative) heat loss from sheep, which used the relation between heat flow, thermal insulation and the difference between body and environmental temperatures.Clothing insulation for man is estimated in two ways: as clothing (I_c) that is impervious to the effects of wind and rain; and as the equivalent depth of sheep fleece (f_m), which is not impervious. This allows the assessment of wind chill for a range of clothing of varied penetration by wind instead of for only one type of garment.Results are given as daily means calculated from hourly measurements throughout 1973 for Plymouth (on the south coast of Britain) and Aberdeen (on the far northeast coast of Britain). Wind chill is estimated both by its effect on f_m requirement and by the fall in air temperature that would be needed to produce under still-air conditions the same demand for f_m that occurs in the actual environment. The monthly mean f_m requirement is reduced by about 40% when the effect of wind is removed. When wind chill is estimated as an equivalent fall in air temperature it approximates to 1 K per knot wind speed measured at the standard meteorological height of 10 m.     

Relationships between integumental characteristics and thermoregulation in South American camelids

Hair fibre is regarded as a unique mammalian feature with an important role for endothermy. Artificial selection for hair characteristics resulted in marked changes with regard to follicle number, type, distribution, growth and natural shedding. This review focuses on the fine fibre-producing South American camelids (SACs) and the relationship between their hair coat and thermoregulation. SACs have developed several special integumental characteristics. While the hair coat of the wild lamoids vicuña (Vicugna vicugna) and guanaco (Lama guanicoe) is formed by two types of hair (the coarse outer guard hairs and a finer undercoat), the domesticated llamas (Lama glama) and alpaca (Lama pacos) exhibit variably double coat and predominantly single coat, respectively. The distribution of the hair coat across the body is not homogenous. Thermal windows with shorter hair or thinner skin can be identified at the ventral abdomen, axillary space and inside of the thighs (about 20% of the skin), thus allowing to modulate heat dissipation. In contrast to sheep wool, lamoid fibres are mainly medullated. The thermal conductance of summer pelage was higher than that of the winter fleece and highest for the axillar and lower flanks. Lamoids have developed behavioural strategies to modify heat loss by adopting specific postures according to ambient conditions by closing or opening the thermal windows. Energy savings of 67% attributed to posture were calculated. SACs have shown to be able to adapt to a broad range of different climatic conditions. The specific integumental characteristics of SACs indicate that they have developed adaptation mechanisms particularly suited for cooler climates. Accordingly, hyperthermia might become a problem in hot, humid areas outside of their original habitat. Several studies showed the beneficial effect of shearing against heat stress. In particular, fertility in males exposed to heat stress may be improved by shearing. Infrared thermography reveals that in shorn animals the heat is radiated across the entire body surface and is not restricted to the thermal windows. However, shearing also changes the conditions of the protective layer, resulting in a loss of thermal conductance that may result in adverse effects when animals are kept under cold temperatures. The length of residual fibre appears to be crucial in avoiding excessive heat loss in a cold environment, as demonstrated by shearing experiments with different shearing machines. There is, therefore, potential for welfare considerations to conflict with industrial demands for fibre length or homogenous quality.     

The Mechanism of Amino Acid Efflux from Seed Coats of Developing Pea Seeds as Revealed by Uptake Experiments

The uptake of amino acids by excised seed coat halves of developing seeds of pea (Pisum sativum L.) was characterized. The influx of L-valine and L-glutamic acid was proportional to their external concentration, with coefficients of proportionality (k) of 11.0 and 7.1 [mu]mol g-1 fresh weight min-1 M-1, respectively. The influx of L-lysine could be analyzed into a component with linear kinetics (k = 8.1 [mu]mol g-1 fresh weight min-1 M-1) and one with saturation kinetics (Michaelis constant = 6.5 mM), but the latter may have resulted from the mutual interaction between the influx of the cationic lysine and the membrane potential. The influx of the amino acids was not affected by 10 [mu]M carbonylcyanide m-chlorophenylhydrazone, but was inhibited by about 50% in the presence of 2.5 mM p-chloromercuribenzene sulfonic acid. Conservative estimates of the permeability coefficients of the plasma membrane of seed coat parenchyma cells for lysine, glutamic acid, and several neutral amino acids were all in the range of 4 x 10-7 cm s-1 to 9 x 10-7 cm s-1, which is 4 to 5 orders of magnitude greater than those reported for artificial lipid bilayers. It is concluded that nonselective pores constitute a pathway in the plasma membrane for passive transport of amino acids. It is argued that this pathway is also used for the efflux of endogenous amino acids, the process by which nitrogen becomes available for the embryo.     

Modification of carboplatin by Jurkat cells

Using [(1)H,(15)N] heteronuclear single quantum coherance (HSQC) NMR and (15)N-labeled carboplatin, 1, we show that Jurkat cells affect the rate of disappearance of the HSQC NMR peak in culture medium for this Pt(2+) anticancer drug. The decay or disappearance rate constant for 1 in culture medium containing cells is k(1)=k(c)[CO(3)(2-)]+k(m)+k(u)N, where k(c) is the rate constant for reaction of 1 with carbonate in the medium, k(m) is the rate constant for reaction of 1 with all other components of the medium, and k(u) is the rate constant for reaction of 1 with cells having a number density N in the medium. Since Jurkat cells only take up a small amount of the platinum present in the medium (<1%), the observed disappearance of the HSQC NMR peak for 1 cannot be due to uptake of carboplatin by the cells.     

Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals

We quantified metabolic power consumption as a function of wind speed in the presence and absence of simulated solar radiation in rock squirrels, Spermophilus variegatus, a diurnal rodent inhabiting arid regions of Mexico and the western United States. In the absence of solar radiation, metabolic rate increased 2.2-fold as wind speed increased from 0.25 to 4.0 m·s^-1. Whole-body thermal resistance declined 56% as wind speed increased over this range, indicating that body insulation in this species is much more sensitive to wind disruption than in other mammals. In the presence of 950 W·m^-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0 m·s^-1. Solar heat gain, calculated as the reduction in metabolic heat production associated with the addition of solar radiation, increased with wind speed from 1.26 mW·g^-1 at 0.25 m·s^-1 to 2.92 mW·g^-1 at 4.0 m·s^-1. This increase is opposite to theoretical expectations. Both the unexpected increase in solar heat gain at elevated wind speeds and the large-scale reduction of coat insulation suggests that assumptions often used in heat-transfer analyses of animals can produce important errors.Abbreviations absorptivity of coat to solar radiation - kinematic viscosity of air (mm²·s^-1) - reflectivity of coat to solar radiation - a r _B expected at zero wind speed (s·m^-1) - A _P projected surface area of animal on plane perpendicular to solar beam (cm²) - A _SKIN skin surface area (cm²) - b Coefficient describing change in r _B with change in square-root of wind speed (s^1.5·m^1.5) - d hair diameter (m) - d characteristic dimension of animal (m) - D _H thermal diffusivity of air (m²·s^-1) - E evaporative heat loss (W·m^-2) - I probability per unit coat depth that photon will strike hair - k constant equalling 1200 J·m^-3·°C^-1 - l _C coat depth m) - l _H hair length (m) - M metabolic rate (W·m^-2) - n density of hairs of skin (m^-2) - Q _A solar heat gain to animal (W·m^-2) - Q _I solar irradiance intercepted by animal (W·m^-2) - RQ respiratory quotient - r _A thermal resistance of boundary layer (s·m^-1) - r _B whole-body thermal resistance (s·m^-1) - r _E thermal resistance between animal surface and environment s·m^-1) - r _R radiative resistance (s·m^-1) - r _S sum of r _B and r _E at 0.25 m·s^-1 (s·m^-1) - r _T tissue thermal resistance s·m^-1) - T _AIR air temperature (°C) - T _B body temperature (°C) - T _E operative temperature of environment (°C) - T _ES standard operative temperature of environment (°C) - u wind speed (m·s^-1)     

Reduction of horse heart ferricytochrome c by bovine liver ferrocytochrome b5. Experimental and theoretical analysis.

The reduction of horse heart ferricytochrome c by the tryptic fragment of bovine liver cytochrome b5 and its dimethyl ester heme (DME)-substituted derivative has been studied as a function of ionic strength, pH, and temperature under solution conditions where the reaction is bimolecular. The rate constant for ferricytochrome c reduction by native ferrocytochrome b5 is 1.8 (+/- 0.2) x 10(7) M-1 s-1 (25 degrees C) with delta H++ = 7.5 (+/- 0.2) kcal/mol and delta S++ = -0.3 (+/- 0.6) eu (pH 7.0, I = 0.348 M). Under the same solution conditions, the reduction of ferricytochrome c by DME-ferrocytochrome b5 proceeds with a rate constant of 1.7 (+/- 0.1) x 10(7) M-1 s-1 with delta H++ = 7.9 (+/- 0.4) kcal/mol and delta S++ = 1 (+/- 1) eu. The rate constants for both reactions are strongly dependent on ionic strength. A detailed electrostatic analysis of the proteins has been performed. Two relatively simple Brownian dynamics simulation models predict rate constants for the reaction between the two native proteins that demonstrate a dependence on ionic strength similar to that observed experimentally. In one of these models, the proteins are treated as spheres with reactive surface patches that are defined by a 5 degrees cone generated about the dipole vector calculated for each protein and aligned with the presumed electron-transfer site near the partially exposed heme edge. The second model replaces the reactive patch assumption with an exponential distance dependence for the probability of reaction that permits estimation of a value for the distance-dependence factor alpha. Calculations with this latter model in combination with the aligned dipole assumption provide a reasonable approximation to the observed ionic strength dependence for the reaction and are consistent with a value of alpha = 1.2 A-1.     

Kinetic study on the successive four-step reduction of Cyt c3

A detailed kinetic study on the successive four-step reduction of cyt c3, which has four heme units in a single protein, III4 leads to III3II leads to III2II2 leads to III II3 leads to II4, was carried out by stopped-flow electronic spectroscopy (SF-UV) and stopped-flow circular dichroism spectroscopy (SF-CD). Based on the absorbance change vs. time and the ellipticity change vs. time at the characteristic CD, together with the electronic absorption of the enzyme, rate constants for the successive four electron transfer steps, k1-k4, were successfully estimated by computer simulation. The rate constants of the four steps (k1 = 19.8 s-1, k2 = 11.9 s-1, k3 = 8.9 s-1, and k4 = 1.6 s-1; 8.0 10(-4) M Na2S2O4) are quite different from the statistical values (4: 3: 2: 1), thus excluding the possibility of random reduction of hemes of equal reactivities. Instead, each heme has its own reactivity, probably dependent on its local environment. The value of k3 is somewhat higher than the statistical value, indicating the existence of an autoacceleration effect, although small. This autoacceleration is most probably due to a unique heme-heme and/or heme-environment interaction since unusual CD and electronic absorptions were observed at 350-400 nm at about the time corresponding.     

Consequences of skin color and fur properties for solar heat gain and ultraviolet irradiance in two mammals

Summary In animals with fur or feather coats, heat gain from solar radiation is a function of coat optical, structural, and insulative characteristics, as well as skin color and the optical properties of individual hairs or feathers. In this analysis, I explore the roles of these factors in determining solar heat gain in two desert rodents (the Harris antelope squirrel,Ammospermophilus harrisi, and the round-tailed ground squirrel,Spermophilus tereticaudus). Both species are characterized by black dorsal skin, though they contrast markedly in their general coat thickness and structure. Results demonstrate that changes in coat structure and hair optics can produce differences of up to 40% in solar heat gain between animals of similar color. This analysis also confirms that the model of Walsberg et al. (1978) accurately predicts radiative heat loads within about 5% in most cases. Simulations using this model indicate that dark skin coloration increases solar heat gain by 5%. However, dark skin significantly reduces ultraviolet transmission to levels about one-sixth of those of the lighter ventral skin.Symbols and abbreviations: (unless noted, all radiation relations refer to total solar radiation) absorptivity of individual hairs - _C absorptivity of the coat - backward scattering coefficient [reflectivity] of individual hairs - _C reflectivity of coat - _S reflectivity of skin - forward scattering coefficient [transmissivity] of individual hairs - _C transmissivity of coat - _S transmissivity of the skin - transmissivity of the coat and skin - transmissivity of the coat to ultraviolet radiation - _S transmissivity of the skin to ultraviolet radiation - [(1 – )² – ²] - h _C coat thermal conductance [W/m²-°C] - h _E coat surface-to-environment thermal conductance [W/m²-°C] - I probability per unit coat depth that a ray will be intercepted by a hair [m^–1] - K volumetric specific heat of air at 20°C [1200 J/m³-°C] - l _C coat thickness [m] - l _H hair length [m] - d hair diameter [m] - n hair density per unit skin area (m^–2] - Q _ABS heat load on animal's skin from solar radiation [W/m²] - Q _I solar irradiance at coat surface [W/m²] - r _E external resistance to convective and radiative heat transfer [s/m] - r _C coat thermal resistance [s/m]     

Studies on rat liver plasma membrane. Altered protein and phospholipid metabolism after injection of D-galactosamine.

The displacement of NADH from cytoplasmic aldehyde dehydrogenase (EC 1.2.1.3) from sheep liver was studied by using NAD+, 1,10-phenanthroline, ADP-ribose, deamino-NAD+ and pyridine-3-aldehyde-adenine dinucleotide as displacing agents, by following the decrease in fluorescence as a function of time. The data obtained could be fitted by assuming two first-order processes were occurring, a faster process with an apparent rate constant of 0.85 +/- 0.20 s-1 and a relative amplitude of 60 +/- 10% and a slower process with an apparent rate constant of 0.20 +/- 0.05 s-1 and a relative amplitude of 40 +/- 10% (except for pyridine-3-aldehyde-adenine dinucleotide, where the apparent rate constant for the slow process was 0.05 s-1). The displacement rates did not change significantly when the pH was varied from 6.0 to 9.0. Kinetic data are also reported for the dependence of the rate of binding of NADH to the enzyme on the total concentration of NADH. Detailed arguments are presented based on the isolation and purification procedures, the equilibrium coenzyme-binding studies and the kinetic data, which lead to the following model for the release of NADH from the enzyme: (formula: see article). The parameters that best fit the data are: k + 1 = 0.2 s-1; k - 1 = 0.05 s-1; k + 2 = 0.8 s-1 and k - 2 = 5 X 10(5)litre-mol-1-s-1. The slow phase of the NADH release is similar to the steady-state turnover number for substrates such as acetaldehyde and propionaldehyde and appears to contribute significantly to the limitation of the steady-state rate.