Evidence for two domains of growth temperature for the psychrotrophic bacterium Pseudomonas fluorescens MF0.

The variations in the maximal specific growth rate of the psychrotrophic bacterium Pseudomonas fluorescens MF0 with respect to temperature were studied between 0 and 30 degrees C (optimal for growth). The Arrhenius plot showed a drastic change in slope at the intermediate temperature of 17 degrees C. Over the cold domain from 0 to 17 degrees C, the temperature characteristic was twofold higher than over the suboptimal domain from 17 to 30 degrees C. The macromolecular composition of exponentially growing cells was invariant over the entire range from 0 to 30 degrees C. Variations of temperature and growth rate were independently investigated through chemostat experiments in order to characterize their respective effects on cell macromolecular composition and size. The effect of growth rate in this psychrotrophic strain is identical to that of all other bacteria assayed so far. In contrast, an original biphasic variation of total protein concentration was demonstrated in strain MF0 with respect to temperature, with a maximum at 17 to 20 degrees C. Indeed, increasing the temperature in the chemostat resulted in a biphasic decrease in the net protein production rate: a very slight decrease below 17 degrees C and a much larger decrease from 17 to 28 degrees C. These results could signify an increase in the cellular protein degradation rate with increasing temperature, especially above 17 degrees C.     

Effects of extremely hot days on people older than 65 years in Seville (Spain) from 1986 to 1997

The effects of heat waves on the population have been described by different authors and a consistent relationship between mortality and temperature has been found, especially in elderly subjects. The present paper studies this effect in Seville, a city in the south of Spain, known for its climate of mild winters and hot summers, when the temperature frequently exceeds 40 degrees C. This study focuses on the summer months (June to September) for the years from 1986 to 1997. The relationships between total daily mortality and different specific causes for persons older than 65 and 75 years, of each gender, were analysed. Maximum daily temperature and relative humidity at 7.00 a.m. were introduced as environmental variables. The possible confounding effect of different atmospheric pollutants, particularly ozone, were considered. The methodology employed was time series analysis using Box-Jenkins models with exogenous variables. On the basis of dispersion diagrams, we defined extremely hot days as those when the maximum daily temperature surpassed 41 degrees C. The ARIMA model clearly shows the relationship between temperature and mortality. Mortality for all causes increased up to 51% above the average in the group over 75 years for each degree Celsius beyond 41 degrees C. The effect is more noticeable for cardiovascular than for respiratory diseases, and more in women than in men. Among the atmospheric pollutants, a relation was found between mortality and concentrations of ozone, especially for men older than 75.     

Effects of cell density and temperature on oxygen consumption rate for different mammalian cell lines.

Oxygen consumption rates were measured in a respirometer for different mammalian cell lines (BHK, murine hybridoma, and CHO), and the effects of cell density (1-20 million cells/mL) and temperature (6 to 37 degrees C) on specific oxygen consumption rate were investigated. The specific oxygen consumption was cell line dependent. For a given temperature, the murine hybridoma cells had the lowest and the CHO cells had the highest oxygen consumption rate. The specific oxygen consumption rate was not affected by the cell concentration for cell densities between 1 and 20 million cells/mL. However, artificial trends implicating the effects of cell density were obtained when traditional analysis was used and the probe response time was neglected. A detailed mathematical analysis was presented to investigate the magnitude of errors originating from neglecting the probe response time for the calculation of oxygen consumption rate. The error was significant, especially when the probe response was slow and/or the oxygen consumption was fast. Temperature influenced the specific oxygen consumption rate similarly for the cells studied, and about 10% decrease was observed in specific oxygen consumption by 1 degrees C decrease in the temperature. Between 6 and 37 degrees C, the effect of temperature on oxygen consumption rate could be described using an Arrhenius model, i.e., qO2 = qoO2. e-E/RT. The activation energy, E, in this equation was similar for different cells (between 80 and 90 kJ/mol), indicating the action of a similar mechanism for the effect of temperature on oxygen consumption.     

Effects of cooling and warming rate to and from -70 degrees C, and effect of further cooling from -70 to -196 degrees C on the motility of mouse spermatozoa

We have previously reported high survival in mouse sperm frozen at 21 degrees C/min to -70 degrees C in a solution containing 18% raffinose in 0.25 x PBS (400 mOsm) and then warmed rapidly at approximately 2000 degrees C/min, especially under lowered oxygen tensions induced by Oxyrase, a bacterial membrane preparation. The best survival rates were obtained in the absence of glycerol. The first concern of the present study was to determine the effects of the cooling rate on the survival of sperm suspended in this medium. The sperm were cooled to -70 degrees C at rates ranging from 0.3 to 530 degrees C/min. The survival curve was an inverted "U" shape, with the highest motility occurring between 27 and 130 degrees C/min. Survival decreased precipitously at higher cooling rates. Decreasing the warming rate, however, decreased survivals at all cooling rates. The motility depression with slow warming was especially evident in sperm cooled at the optimal rates. This fact is consistent with our current view that the frozen medium surrounding sperm cells is in a metastable state, perhaps partly vitrified as a result of the high concentrations of sugar. The decimation of sperm cooled more rapidly than optimum (>130 degrees C/min), even with rapid warming, is consistent with the induction of considerable quantities of intracellular ice at these rates. When glycerol was added to the above medium, motilities were also dependent on the cooling rate, but they tended to be substantially lower than those obtained in the absence of glycerol. The minimum temperature in the above experiments was -70 degrees C. When sperm were frozen to -70 degrees C at optimum rates, lowering the temperature to -196 degrees C had no adverse effect.     

Pre-adult mortality in the blowfly Lucilia sericata

Populations of the blowfly, Lucilia sericata (Meigen) (Diptera: Calliphoridae), have a considerable potential for rapid increase; the lifetime reproductive output of each adult female has been estimated to be between 130 and 172 eggs. Nevertheless, in the field, absolute population densities of this species are relatively low. To account for this difference, the levels of mortality affecting the eggs, feeding and wandering larvae and pupae of L. sericata were assessed in the field and laboratory. Percentage egg hatch was dependent on relative humidity with no egg eclosion at humidities below 50%; there was no significant effect of temperature on egg hatch. On infested sheep, the mean mortality of feeding larvae was 53%, but this ranged widely from 0% to 96%. There was no effect of atmospheric temperature or humidity on the mortality of feeding larvae in vivo. In the laboratory, only 10% of wandering larvae pupariated at 10 degrees C. At above 20 degrees C pupariation was consistently almost 100%. Percentage emergence increased from 0% at 10 degrees C to about 80% between 20 and 30 degrees C. The upper lethal temperature for pupae was approached at 35 degrees C. Analysis of the predation of pupae in the field revealed a weak, but significant curvilinear relationship between temperature and proportionate mortality and a median mortality of 0.49% per 24 h exposure (interquartile range = 5.2%). There was no evidence of density dependence in pupal predation. Overall, it is estimated that pre-adult mortality accounts for losses of approximately 97% of each generation, but this figure is subject to considerable variation depending on factors such as climate, time of year and host susceptibility.     

Size-dependent pigmentation-pattern formation in embryos of Alligator mississippiensis: time of initiation of pattern generation mechanism

The pigmentation pattern of Alligator mississippiensis was examined. The number of white stripes on the dorsal side of embryos (stages 21-28) and hatchlings from eggs incubated at 30 degrees C (100% females) and 33 degrees C (100% males) was recorded. Total length, nape-rump length and tail length were recorded for each embryo and hatchling. The number of white stripes was affected by incubation temperature but not sex; hatchlings incubated at 33 degrees C had two more white stripes than those at 30 degrees C, despite being the same length. Five female hatchlings produced at 33 degrees C by manipulation of the temperature, had the same number of stripes as males that developed under the same incubation temperatures. The appearance of the pigmentation was accelerated in embryos incubated at 33 degrees C, occurring eight days earlier than at 30 degrees C. At the time just before the first signs of pigment deposition, embryos from 33 degrees C were longer than those at 30 degrees C. If the stripe formation is size dependent this explains why hatchlings at 33 degrees C have more stripes than hatchlings from 30 degrees C. The mechanism that produces the stripe patterns is unknown. We describe key elements a pattern formation mechanism must possess to produce such stripes and suggest a possible mechanism, based on cell movement driven by chemotaxis. We apply the mathematical model to dorsal patterning on A. mississippiensis. We show how length at pattern formation is the prime factor in determining stripe number and how the pattern can be formed in the observed anterior-posterior sequence. We present numerical simulations and show that the qualitative behaviour is consistent with the experimental results.     

Thermal degradation processes of end-capped poly(L-lactide)s in the presence and absence of residual zinc catalyst

Thermal degradation processes of end-capped poly(L-lactide)s (PLLAs) were investigated by means of several thermoanalytical techniques under both isothermal and nonisothermal conditions. Based on the thermogravimetric analysis, it was found that two distinct processes at temperatures below and above 330 degrees C were existed in the nonisothermal degradation for PLLA samples depending on the amounts of residual zinc compounds from synthesis process. Isothermal degradation experiments at different temperature regions showed that the sample weight of PLLA decreased linearly with time in both cases, whereas the changes in molecular weight revealed different tendency for the temperature. On the basis of characterization of the residual PLLA molecules after isothermal degradation at 330 degrees C, it was confirmed that the omega chain end of the residual molecules was an acrylic ester unit. Majority of volatile products during thermal degradation of PLLA was the lactide regardless of the degradation temperature. From these results, it is concluded that, during the thermal degradation of PLLA samples in the presence of large amounts of residual zinc compounds, the zinc compounds catalyze both the intermolecular transesterification generating PLLA with low molecular weights and the selective unzipping depolymerization of PLLA with low molecular weights at temperatures below 330 degrees C. In contrast, the primary reaction of thermal degradation for PLLA in the absence of residual zinc compounds above 330 degrees C is a competition between the random chain scission via a cis-elimination reaction and the cyclic rupture via intramolecular transesterification of PLLA molecules. In addition, it was evidenced that the racemization of lactic acid units in the main chain of PLLA molecules occurred at temperatures above 330 degrees C.     

Zinc-coordination of aspartic acid-76 in Sulfolobus ferredoxin is not required for thermal stability of the molecule

The highly thermostable 7Fe-ferredoxin from Sulfolobus sp. strain 7 has tightly bound zinc at the interface between the N-terminal extra domain and the C-terminal core. The zinc is tetrahedrally ligated by His-16, His-19, His-34, and Asp-76. Previous studies on truncated mutants have shown that the zinc and certain parts, i.e. not all, of the N-terminal extra stretch are responsible for the thermal stabilization of the molecule. To study the role of Asp-76, a series of mutants were constructed with Asp-76 replaced by Glu (D76E), Asn (D76N), or Ala (D76A). All the mutants, as well as wild type ferredoxin, bound 1 mol zinc/mol protein, and showed similar kinetics for 2-oxoacid:ferredoxin oxidoreductase. The stability of the protein was examined by thermal degradation of the clusters. In the absence of guanidium thiocyanate, the T(m), defined as the mid-point temperature of the thermal transition from the native to the denatured state, for every mutant was above 100 degrees C. The T(m) values in the presence of 1 M guanidium thiocyanate were determined to be 90.8, 90.2, 87.1, 84.4, and 72.9 degrees C for the natural, recombinant, D76N-, D76A-, and D76E-ferredoxins, respectively. These results indicate that the interaction between zinc and the carboxyl oxygen of Asp-76 has subtle effects on both the zinc-ligation and stability, although the native zinc center is liganded with high symmetry, suggesting that the three His residues are more important for zinc-binding.     

Respiratory response to temperature and hypoxia in the zebra mussel Dreissena polymorpha

The effects of temperature acclimation, acute temperature variation and progressive hypoxia on oxygen consumption rates (VO2) were determined for the zebra mussel Dreissena polymorpha. In the first experiment, after acclimation to 5, 15 or 25 degrees C for at least 2 weeks, VO2 was determined at 5 degrees C increments from 5 to 45 degrees C. VO2 increased in all three acclimation groups from 5 to 30 degrees C, corresponding to the normal ambient temperature range for this species. Mussels displayed imperfect temperature compensation at temperatures above 15 degrees C, but exhibited little acclimatory ability below 15 degrees C. In the hypoxia experiment, VO2 was determined over the course of progressive hypoxia, from full saturation (oxygen tension [PO2]=160 Torr [21.3 kPa]) to a PO2 at which oxygen uptake ceased (<10 Torr [1.3 kPa]). Mussels were acclimated to either 5, 15 or 25 degrees C for at least 2 weeks and their respiratory response to progressive hypoxia was measured at three test temperatures (5, 15 and 25 degrees C). The degree of oxygen regulation increased with increasing test temperature, particularly from 5 to 15 degrees C, but decreased with increasing acclimation temperature. The decreased metabolic rate observed for warm-acclimated animals, particularly in the upper portion of the temperature range of the zebra mussel, may allow for conservation of organic energy stores during warm summer months. Compared to other freshwater bivalves, D. polymorpha is a relatively poor oxygen regulator, corresponding with its preference for well-oxygenated aquatic habitats. In addition, a new quantitative method for determining the degree of oxygen regulation is presented.     

Effect of Ca2+-Mg2+ exchange on the flexibility and/or conformation of the small domain in monomeric actin.

A fluorescence resonance energy transfer (FRET) parameter, f' (defined as the average transfer efficiency, (E), normalized by the actual fluorescence intensity of the donor in the presence of acceptor, F(DA)), was previously shown to be capable of monitoring both changes in local flexibility of the protein matrix and major conformational transitions. The temperature profile of this parameter was used to detect the change of the protein flexibility in the small domain of the actin monomer (G-actin) upon the replacement of Ca2+ by Mg2+. The Cys-374 residue of the actin monomer was labeled with N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) to introduce a fluorescence donor and the Lys-61 residue with fluorescein-5-isothiocyanate (FITC) to serve as an acceptor. The f' increases with increasing temperature over the whole temperature range for Mg-G-actin. This parameter increases similarly in the case of Ca-G-actin up to 26 degrees C, whereas an opposite tendency appears above this temperature. These data indicate that there is a conformational change in Ca-G-actin above 26 degrees C that was not detected in the case of Mg-G-actin. In the temperature range between 6 degrees C and 26 degrees C the slope of the temperature profile of f' is the same for Ca-G-actin and Mg-G-actin, suggesting that the flexibility of the protein matrix between the two labels is identical in the two forms of actin.     

Anaerobic biodegradation of 2,4-dichlorophenol in freshwater lake sediments at different temperatures

Anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) between 5 and 72 degrees C was investigated. Anaerobic sediment slurries prepared from local freshwater pond sediments were partitioned into anaerobic tubes or serum vials, which then were incubated separately at the various temperatures. Reductive 2,4-DCP dechlorination occurred only in the temperature range between 5 and 50 degrees C, although methane was formed up to 60 degrees C. In sediment samples from two sites and at all tested temperatures from 5 to 50 degrees C, 2,4-DCP was transformed to 4-chlorophenol (4-CP). The 4-CP intermediate was subsequently degraded after an extended lag period in the temperature range from 15 to 40 degrees C. Adaptation periods for 2,4-DCP transformation decreased between 5 and 25 degrees C, were essentially constant between 25 and 35 degrees C, and increased in the tubes incubated at temperatures between 35 and 40 degrees C. The degradation rates increased exponentially between 15 and 30 degrees C, had a second peak at 35 degrees C, and decreased to about 5% of the peak activity by 40 degrees C. In tubes from one sediment sample, incubated at temperatures above 40 degrees C, an increase in the degradation rate was observed following the minimum at 40 degrees C. This suggests that at least two different organisms were involved in the transformation of 2,4-DCP to 4-CP. Storage of the original sediment slurries for 2 months at 12 degrees C resulted in increased adaptation times, but did not affect the degradation rates.     

Anaerobic biodegradation of 2,4-dichlorophenol in freshwater lake sediments at different temperatures.

Anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) between 5 and 72 degrees C was investigated. Anaerobic sediment slurries prepared from local freshwater pond sediments were partitioned into anaerobic tubes or serum vials, which then were incubated separately at the various temperatures. Reductive 2,4-DCP dechlorination occurred only in the temperature range between 5 and 50 degrees C, although methane was formed up to 60 degrees C. In sediment samples from two sites and at all tested temperatures from 5 to 50 degrees C, 2,4-DCP was transformed to 4-chlorophenol (4-CP). The 4-CP intermediate was subsequently degraded after an extended lag period in the temperature range from 15 to 40 degrees C. Adaptation periods for 2,4-DCP transformation decreased between 5 and 25 degrees C, were essentially constant between 25 and 35 degrees C, and increased in the tubes incubated at temperatures between 35 and 40 degrees C. The degradation rates increased exponentially between 15 and 30 degrees C, had a second peak at 35 degrees C, and decreased to about 5% of the peak activity by 40 degrees C. In tubes from one sediment sample, incubated at temperatures above 40 degrees C, an increase in the degradation rate was observed following the minimum at 40 degrees C. This suggests that at least two different organisms were involved in the transformation of 2,4-DCP to 4-CP. Storage of the original sediment slurries for 2 months at 12 degrees C resulted in increased adaptation times, but did not affect the degradation rates.     

Characterization of an activity from the strict anaerobe Roseburia cecicola that degrades DNA when exposed to air.

Roseburia cecicola is an obligately anaerobic bacterium that is extremely sensitive to oxygen. Genomic DNA isolated from cells exposed to air for even a brief period (< 5 min) is partially degraded, while DNA extracted from cells maintained in an anaerobic environment remains intact. Cells exposed to air for longer and longer periods yield DNA which is progressively degraded into fragments with decreasing sizes. Oxygen toxicity for this anaerobe appears to result, at least in part, from degradation of its genomic DNA. Cell lysates of the organism exhibited a similar ability to degrade exogenous sources of DNA when assayed in vitro under aerobic conditions. A substance that degrades both DNA and RNA when incubated aerobically was partially purified from such lysates. It has an approximate molecular weight of 2,800 and is unlikely to be a protein. It requires a reducing agent for activity and can be inhibited by catalase and peroxidase but not superoxide dismutase. The rate at which it degrades DNA in vitro can be enhanced by temperatures above 37 degrees C or by oxygen at partial pressures above atmospheric pressure. These results suggest that this substance degrades nucleic acids by a mechanism involving oxygen radicals.     

A mathematical model of electron transfer within the mitochondrial respiratory cytochromes

A simple mathematical model of electron flow along the mitochondrial respiratory cytochrome assembly and the transfer of electrons to molecular oxygen is presented. First, an expression for the current-voltage relationship for a biological oxygen electrode is derived, and from this the relationship between oxygen consumption rate and oxygen partial pressure is determined. An independent relationship between mitochondrial oxygen partial pressure and oxygen supply rate is then derived. By eliminating oxygen partial pressure from these two expressions, we may obtain a relationship between oxygen supply rate and oxygen consumption rate. This model is then used to investigate the effects of tissue dysoxia, uncoupling of oxidative phosphorylation, increased cellular diffusional resistance and inhomogeneities in oxygen supply on oxygen consumption. It is concluded that each of the above contribute in varying degrees to the phenomenon of "pathological oxygen supply dependency".     

An analysis of the effect of changes in growth temperature on proteolysis in vivo in the psychrophilic bacterium Vibrio sp. strain ANT-300.

In the psychrophilic bacterium Vibrio sp. strain ANT-300, the rate of protein degradation in vivo, measured at fixed temperatures, increased with elevation of the growth temperature. A shift in growth temperature induced a marked increase in this rate. Dialysed cell-free extracts hydrolysed exogenous insulin, globin and casein (in decreasing order of activity) but did not hydrolyse exogenous cytochrome c. Cells contained at least seven protease separated by DEAE-Sephacel chromatography, one of which was an ATP-dependent serine protease. The ATP-dependent proteolytic activity in extracts of cells incubated for 3 h at 16 degrees C after a shift-up from 0 degrees C increased to a level 36% and 17% higher than that of cells grown at 0 degrees C and 13 degrees C, respectively. A shift-down to 0 degrees C from 13 degrees C induced only a slight increase in the proteolytic activity. Extracts of all cells, whether exposed to temperature shifts or not, showed the same temperature dependence with respect to both ATP-dependent and ATP-independent protease activity. In all the extracts these proteases also exhibited the same heat lability. The ATP-dependent protease was inactivated by incubation at temperatures above 25 degrees C. There was an increase in ATP-independent protease activity during incubation at temperatures between 25 and 30 degrees C, but a decrease at 35 degrees C and higher. These results suggest that the marked increases in proteolysis in vivo, caused by a shift in temperature, may result not only from increases in levels of ATP-dependent serine protease(s) but also from increases in the susceptibility of proteins to degradation.     

Temperature-dependent function of the glutamine phosphoribosylpyrophosphate amidotransferase ammonia channel and coupling with glycinamide ribonucleotide synthetase in a hyperthermophile

Genes encoding glutamine phosphoribosylpyrophosphate amidotransferase (GPAT) and glycinamide ribonucleotide synthetase (GARS) from Aquifex aeolicus were expressed in Escherichia coli, and the enzymes were purified to near homogeneity. Both enzymes were maximally active at a temperature of at least 90 degrees C, with half-lives of 65 min for GPAT and 60 h for GARS at 80 degrees C. GPAT activity is known to depend upon channeling of NH(3) from a site in an N-terminal glutaminase domain to a distal phosphoribosylpyrophosphate site in a C-terminal domain where synthesis of phosphoribosylamine (PRA) takes place. The efficiency of channeling of NH(3) for synthesis of PRA was found to increase from 34% at 37 degrees C to a maximum of 84% at 80 degrees C. The mechanism for transfer of PRA to GARS is not established, but diffusion between enzymes as a free intermediate appears unlikely based on a calculated PRA half-life of approximately 0.6 s at 90 degrees C. Evidence was obtained for coupling between GPAT and GARS for PRA transfer. The coupling was temperature dependent, exhibiting a transition between 37 and 50 degrees C, and remained relatively constant up to 90 degrees C. The calculated PRA chemical half-life, however, decreased by a factor of 20 over this temperature range. These results provide evidence that coupling involves direct PRA transfer through GPAT-GARS interaction rather than free diffusion.     

Combined heat and controlled atmosphere quarantine treatments for control of western cherry fruit fly in sweet cherries

Nonchemical quarantine treatments, using a combination of short duration high temperatures under low oxygen, elevated carbon dioxide atmospheric environment were developed to control western cherry fruit fly, Rhagoletis indifferens Curran, in sweet cherries, Prunus avium (L.). The two treatments developed use a chamber temperature of 45 degrees C for 45 min and a chamber temperature of 47 degreesd C for 25 min, both under a 1% oxygen, 15% carbon dioxide, -2 degrees C dew point environment. Both these treatments have been shown to provide control of all life stages of western cherry fruit fly while preserving commodity market quality. There was no definitive egg or larval stage, which was demonstrated to be the most tolerant to either controlled atmosphere temperature treatment system treatment. Efficacy tests for both treatments resulted in 100% mortality of >5000 western cherry fruit flies in each treatment. These treatments may provide, with further study, quarantine security in exported sweet cherries where western cherry fruit fly is a quarantine concern and fumigation with methyl bromide is not desired.     

The influence of ambient temperature on metabolism and body temperature of newborn and growing reindeer calves (Rangifer tarandus tarandus L.)

Thermoregulatory capacities of 51 reindeer calves (Rangifer tarandus tarandus L.) aged 1-35 days were studied at -26.5 to +35.0 degrees C ambient temperatures at Kaamanen reindeer research station, Finland (69 degrees 10' N) during calving periods in May 1981 and May-July 1982. The newborn calves aged 1-4 days maintained a high body temperature (Tre) (mean +40.2 degrees C) even at the lowest experimental temperature of -22.5 degrees C by increasing their metabolic rate five-fold above the level at +11.0 degrees C. Heat production of the new-born calves was largely based on the metabolism of brown adipose tissue, stimulated by cold-induced discharge of the sympathetic nervous transmitter, noradrenaline (NA). Sensitivity of the calves to exogenous NA disappeared during the first 3-4 weeks of life. Thermal conductance of the calves was low at low ambient temperatures, but rose strongly as Ta increased above +10 degrees C. The extensive peripheral cooling, especially in the feet, was demonstrated in the calves aged 1-10 days. The lowest foot temperature (+10.5 degrees C) was measured in a 4-day-old calf at -14.5 degrees C. Slight shivering thermogenesis was recorded in the calves aged 1-4 days and occasionally in the older calves at low values of Ta. Shivering appears to be a reserve mechanism against severe cold. At about +20 degrees C and above the calves increased their Tre (approximately 1 degree C), oxygen consumption and heart rate. In the newborn calves oxygen consumption rose four- to five-fold and in 1-month-old calves about two-fold. Fast growing calves (maximum 400 g/day) appear to be more stressed by heat than by cold exposure.     

Purified tomato polygalacturonase activity during thermal and high-pressure treatment

Extracted tomato polygalacturonase was purified by cation-exchange chromatography (and gel filtration) and characterized for molar mass, isoelectric point, as well as optimal pH for polygalacturonase activity. The enzymatic reaction of purified tomato polygalacturonase on polygalacturonic acid as substrate was investigated during a combined high-pressure/temperature treatment in a temperature range of 25 degrees to 80 degrees C and in a pressure range of 0.1 to 500 MPa at pH 4.4 (the pH of tomato-based products). The optimal temperature for initial tomato polygalacturonase activity in the presence of polygalacturonic acid at atmospheric pressure is about 55 degrees to 60 degrees C. The optimal temperature for initial tomato polygalacturonase activity during processing shifted to lower values at elevated pressure as compared with atmospheric pressure, and the catalytic activity of pure tomato polygalacturonase decreased with increasing pressure, which was mostly pronounced at higher temperatures. The elution profiles of the degradation products on high-performance anion-exchange chromatography indicated that for both thermal and high-pressure treatment all oligomers were present in very small amounts in the initial stage of polygalacturonase activity. The amounts of monomer and small oligomers increased with increasing incubation times, whereas the amount of larger oligomers decreased due to further degradation.