Two-substrates packed-bed bioreactors: inhibition of enzyme and competitive binding of substrate and product to a ligand

An analytical model is developed to describe the performance of a packed-bed immobilized enzyme reactor in which parallel processes take place. In particular, two-substrate reaction, inhibition of the enzyme by one of the reaction products, and binding of one substrate and/or one product to an added ligand are taken into account. In addition, substrates and product diffusion into the porous catalyst are also considered. Using this model, numerical simulations were performed. The results point to the fact that, when all the above processes occur concomitantly, a variety of performance characteristics can be obtained, depending on the particular values of the related parameters. Moreover, under certain conditions, the reactor performance can be improved by controlled addition of ligand.List of Symbols A total concentration of ligand - C _1,i concentration of Substrate-1 in the pores of stage i - C _2,i concentration of Substrate-2 in its free form in the pores of stage i - _2,i concentration of the Substrate-2-Ligand Complex in the pores of stage i - total concentration of Substrate-2 in the pores of stage i - _i concentration of the Product-Ligand Complex in the pores of stage i - concentration of the free Product in the pores of stage i - total concentration of the Product in the pores of stage i - internal (pore) diffusion coefficient for the Substrate-Ligand Complex - D ₁ internal (pore) diffusion coefficient of Substrate-1 - D ₂ internal (pore) diffusion coefficient of Substrate-2 - effective (pore) diffusion coefficient for Substrate-2 - internal (pore) diffusion coefficient for the Product - internal (pore) diffusion coefficient for the Product-Ligand Complex - effective (pore) diffusion coefficient for the Product - K thermodynamic equilibrium constant for binding Substrate-2 to Ligand - K _m,1,K _m,2 Michaelis constants for Substrates-1 and 2, respectively - effective Michaelis constant for Substrate-2 - K _p thermodynamic equilibrium constant for binding the reaction Product to Ligand - effective equilibrium constant for binding Substrate-2 to Ligand - effective equilibrium constant for binding the reaction Product to Ligand. - K _b inhibition constant - K _q inhibition constant - effective inhibition constant - effective inhibition constant - k _a, k _d association and dissociation rate constants for Substrate-2 — Ligand complex - association and dissociation constants for Product —Ligand complex - n total number of elementary stages in the reactor - Q volumetric flow rate throughout the reactor - R _j,i reaction rate of Substrate-j in stage i, in terms of volumetric units - S _1,0 concentration of Substrate-1 in the reactor feed - total concentration of Substrate-2 in the reactor feed - S _1,i–1,S _1,i concentration of Substrate-1 in the bulk phase leaving stages i–1 and i, respectively - S _2,i concentration of Substrate-2 in its free form, in the bulk phase leaving stage i - _2,i–1, _2,i concentration of Substrate-2 in the bulk phase leaving stage i–1 and i, respectively - total concentration of Substrate-2 in the bulk phase leaving stages i–1 and i, respectively - _i concentration of the Product-Ligand Complex in the bulk phase of stage i - concentration of free Product in the bulk phase of stage i - total concentration of Product in the bulk phase of stage i - V total volume of the reactor - V _m maximal reaction rate in terms of volumetric units - y axial coordinate of the pores - y ₀ depth of the pores Greek Symbols ₁ dimensionless parameter - dimensionless parameter - dimensionless parameter - ₁ dimensionless parameter - dimensionless parameter - _1,i dimensionless concentration of Substrate-1 in pores of stage i - dimensionless total concentration of Substrate-2 (in both free and bound form) in pores of stage i - dimensionless total concentration of the reaction product in the pores of stage i - ₁ dimensionless parameter - dimensionless parameter - dimensionless parameter - dimensionless parameter - dimensionless parameter - dimensionless position along the pore - volumetric packing density of catalytic particles (dimensionless) - porosity of the catalytic particles (dimensionless) - _1,i dimensionless concentration of Substrate-1 in the bulk phase of stage i - dimensionless total concentration of Substrate-2 (in both free and bound form) in the bulk phase of stage i     

The human V pre B gene is located on chromosome 22 near a cluster of {\text{V}}_{\lambda _1 } gene segments

The chromosomal location of the human V _pre B gene was determined by Southern blotting analysis of restriction enzyme-digested DNAs from a panel of 17 mouse-human somatic cell hybrids. The pattern of hybridization of a V_preB-specific probe in conjunction with earlier analysis of several marker genes allowed the following conclusions: 1) V _pre B is on human chromosome 22 within band 22q11.2 distal to the bcr-like gene, bcr-2 and proximal to the bcr-like gene, bcr-4. 2) V_preB has been localized relative to several constitutional and tumor-specific breakpoints within 22q 11.2, segregates in hybrids retaining 22q^–chromosomes with some but not with all members of the subgroup of the V genes, and is amplified with these genes in K562 cells. 3) The order of the loci on chromosome 22 is centromerebcr-2, V _preB, .     

Theoretical basis of single breath gas absorption tests

Absorption of gas from alveoli is examined in a simplified model of the respiratory system during a stylized single breath consisting of constant inspiratory flow, constant expiratory flow, and breathholding. The equations describing gas behavior are general since they are based upon conservation of mass. The equations simplify considerably when gases that are not soluble in pulmonary tissue and/or blood are utilized. In a three-compartment model, diffusing capacity of the lung for carbon monoxide (D _CO ) will be underestimated except when both uneven distribution of lung volume andD _CO are present; under most circumstances, the standard clinical 10-s method [9] is at least as accurate as any other. When pulmonary capillary blood flow is calculated by the one point method [2] in a one-compartment lung, it is underestimated; in the three-compartment model, it is underestimated except when both uneven distribution of . and lung volume are present. The multiple single breath method [2] accurately measuresD _CO and . Measurement of pulmonary tissue volume is improved by correcting the value of the intercept of acetylene absorption to the time when carbon monoxide apparently began rather than utilizing the beginning of inspiration.Nomenclature D _CO diffusing capacity of the lung for CO (ml CO, STPD/min/mm Hg) - pulmonary capillary blood flow rate (L/min) - V _t pulmonary tissue volume (L) - V _A alveolar compartment volume (L) - V _Ao alveolar compartment volume at conclusion of inspiratory flow (L) - inspiratory flow rate (L/sec) - expiratory flow rate (L/sec) - Bunsen coefficient of pulmonary tissue for test gas (ml test gas/ml tissue/atm) - Bunsen coefficient of pulmonary tissue for test gas (ml test gas/ml blood/atm) - F _A fractional pressure of test gas in the alveolar compartment (atm)     

Estimating the Recombination frequency for the PTC-Kell linkage

Summary Two data sets are analyzed for linkage between the PTC and Kell blood group loci. The original report of close linkage for these loci was that of Conneally et al. (1976), where the maximum likelihood estimate of was 0.05. These two new data sets give a combined maximum likelihood estimate of _m=f =0.28. Estimating the recombination frequency for the sexes separately gave _m =0.29, _f =0.23. The combined maximum likelihood estimate over all published data sets including this report is _m=f =0.14, _max=8.94. There is statistically significant evidence of heterogeneity among the published studies.     

Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus)

Summary The effects of different ambient temperatures (T _a) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m).At both low and high altitude, oxygen consumption ( ) decreased with increasingT _a atT _a from –10 to 30 °C. The was 15–20% smaller at high altitude than at low altitude atT _a below 30 °C.Increased atT _a below thermoneutrality was supported by increased minute volume ( ) at both low and high altitude. At mostT _a, the change in was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (V _T) or oxygen extraction efficiency (O₂EE). AtT _a=0 °C and below at high altitude, was constant due to decliningV _T and O₂EE increased in order to maintain high .At high altitude, (BTP) was 30–40% higher at a givenT _a than at low altitude, except atT _a below 10 °C. The increased at high altitude was due primarily to a proportional increase inf, which attained mean values of 450–500 breaths/min atT _a below 0 °C. The (STP) was equivalent at high and low altitude atT _a of 10 °C and above. At lowerT _a, (STPD) was larger at low altitude.At both altitudes, respiratory heat loss was a small fraction (<10%) of metabolic heat production, except at highT _a (20–30 °C).Abbreviations EHL evaporative heat loss - f respiration frequency - HL _a heat loss from warming tidal air - HL _e evaporative heat loss in tidal air - HL total respiratory heat loss - MHP metabolic heat production - O ₂ EE oxygen extraction efficiency - RQ respiratory quotient - T _a ambient temperature - T _b body temperatureT _lc lower critical temperature - carbon dioxide production - evaporative water loss - oxygen consumption - minute volume - V _T tidal volume     

Dependency as a measure to estimate the order and the values of Markov processes

To evaluate the order and the values of Markov properties of the time series of events, we have proposed a statistical measure dependency:D _m = (H ₀ –H _m )/H ₀ , whereH ₀ andH _m are Shannon's entropy and them-th order conditional entropy, respectively. It is indicated that is a better point estimator ofD _m, giving a total value of them-th order Markov process. Here and are the estimate ofD _m and the arithmetic mean of when them-th order shuffling is made many times for a given observed series, respectively. The value represents Markov value of the orderm. Under the assumption that the series has continuous variables and the normal distribution, simplified dependency is defined by, where |S _m | is the determinant of serial correlation coefficients. It is shown that is practically useful for the estimation of the order and the values of Markov processes with small sample size. It is also indicated that analysis is basically equivalent to the least mean-square analysis of autoregressive models.     

Variation in outcrossing rate and population genetic structure of Clarkia tembloriensis (Onagraceae)

Summary Outcrossing rate estimates for eight accessions of Clarkia tembloriensis indicate that this annual plant species has a wide interpopulational range of outcrossing rate ( ). Populations' t estimates were significantly correlated with observed heterozygosity and mean number of alleles per locus. Estimated fixation indices, , for most populations were very close to their expected values, F_eq, for a given Nei's gene diversity statistics showed that the group of outcrossing populations have more total genetic variation and less differentiation among populations than does the group of selfing populations. These results indicate that the breeding system of C. tembloriensis has had a strong influence on the amount and distribution of genetic variation within and among its populations.     

Mechanisms of potentiation in sweating induced by long-term physical training

To evaluate the mechanism of potentiation of sweating after long-term physical training, we compared sweating function in trained and untrained subjects using the frequency of sweat expulsion (f _sw) as an indicator of central sudomotor activity. Nine trained male subjects (trained group) and eight untrained male subjects (untrained group) performed 30-min cycle exercise at 35% maximal oxygen uptake at 25°C ambient temperature and 35% relative humidity. Oesophageal temperature (T _oes), mean body temperature _b, chest sweating rate ( _sw,chest), forearm sweating rate ( _forearm), andf _sw were measured. The slopes of the _sw,chest versus body temperature (T _oes and _b) and versusf _sw relationships in the trained group were significantly greater than those in the untrained group (both,P < 0.05), while there was no difference between the groups in the slopes of the _sw,chest versus body temperature or versusf _sw relationships. Neither the body temperature threshold for initiation of chest or forearm sweating nor the slope of thef _sw- _b relationship differed between groups. We concluded that, during light exercise at moderate ambient temperature, the _sw,chest in the subjects who had undergone long-term physical training was greater than that in the untrained subjects while the _sw,forearm was not changed. The greater _sw,chest in the trained subjects was concluded to be due to an increase of sensitivity of peripheral mechanisms.     

rDNA magnification in D. melanogaster: state of rDNA copies following the first step.

Summary D. melanogaster males of bb/O genetic constitution undergoing rDNA magnification were mated singly to XXbb ⁺/O females, yielding bb/O male progeny, and to X_NO-w sn bb ⁺ fameles, yielding bb/X_NO- females. The male and female offspring were scored for the bb ⁺ phenotype.Results show that there is a higher percentage of bb ⁺ flies in the bb/O male progeny than in bb/X_NO- females progeny, in single crosses as well as in the combined data. rRNA/DNA hybridization experiments agree with this observation, by showing that the rDNA content in the progeny of premagnified flies was higher in the sons than in the daughters.These data indicate that the increase of ribosomal RNA genes is not due to a stable event such as an unequal mitotic sister exchange, whereas they do not contrast with the extracopy model.     

Temperature induced peripheral blood flow changes in lizards

Summary The influence of local temperature changes within the posterior portion of the body on dorsal aorta blood flow ( ), femoral arterial pressure (P _a ), peripheral resistance (R), skin blood flow ( ) and skeletal muscle blood flow ( ) was examined in unanesthetized lizards (Iguana iguana andTubinambis nigropunctatus). In response to local heating of the hind legs and tail and increased,P _a was generally unchanged,R decreased and decreased or was unchanged (Fig. 2). It is suggested that the acquisition of heat may be favored by diverting the increase in away from the muscle to the warmer skin. In response to cooling and decreased,P _a was generally unchanged, R increased and increased or was unchanged. Hence, during cooling the retention of heat may be favored by diverting blood away from the skin to the deeper muscle. The muscle-skin shunt is under sympathetic control since following blockade with phenoxybenzamine HCL (Dibenzyline) muscle blood flow changes in response to temperature were qualitatively similar to those of skin (Fig. 4). These changes in peripheral circulatory patterns are independent of changes in heart rate or deep body temperature.Baker and Weathers were predoctoral and postdoctoral trainees, respectively, under USPHS Grant HE-05696. This study was also supported by NSF Grant GB-8523 and Los Angeles County Heart Association Grant 437IG.     

Relationship between the octanol-water partition coefficient of tertiary amines and their effect of ‘selective’ uncoupling of photophosphorylation

A series of tertiary amines was investigated for effects on the transmembrane proton potential difference ( H), on photophosphorylation and on electron-flux control related to the intrathylakoid proton potential ( H_I), using isolated chloroplasts ofSpinacia oleracea L. As indicated by 9-aminoacridine fluorescence and [14C]methylamine uptake, all amines studied inhibited a build-up of H and, in parallel, ATP synthesis. Even when H was low, strong H₁-dependent electron-flux control was observed under the influence of tertiary amines. The strength of flux control in the presence of low H and the effectiveness of inhibition of ATP synthesis linearly increased with the lipophilicity of the amines. The most effective of the amines tested caused 50% inhibition of ATP synthesis at a concentration of 6 M, which is about 1000-fold lower than the concentration required for inhibition by methylamine. The data presented indicate the existence of two proton domains in the thylakoid vesicles, one of them feeding the ATP-synthase, the other the sites of pH-dependent electron-flux control. It is concluded that tertiary amines develop their action in a lipophilic domain of the thylakoid membrane, in the vicinity of the ATP-synthase complex. A mechanism for selective uncoupling and for the maintenance of H_I-dependent electron flux control in the presence of low H is discussed.Abbreviations and symbols coefficient for pH-dependent electron flux control - 9-AA 9-aminoacridine - Chl chlorophyll - I₅₀ amine concentration producing 50% inhibition of ATP-synthesis - J_e flux of photosynthetic electron transport - k _H apparent rate constant for proton efflux - H₁ proton potential in the thylakoid lumen - H₁ transthylakoid proton potential difference - p partition coefficient - q _AA coefficient for 9-aminoacridine fluorescence quenching - PS photosystem - Q quantum flux of photosynthetically active light Dedicated to Professor Wilhelm Simonis, on the occasion of his 80th birthday     

A comparison of sweating responses during exercise and recovery in terms of sweating rate and body temperature

Based on the hypothesis that the relation between sweating rate and body temperature should be different during exercise and rest after exercise, we compared the sweating response during exercise and recovery at a similar body temperature. Healthy male subjects performed submaximal exercise (Experiment 1) and maximal exercise (Experiment 2) in a room at 27° C and 35% relative humidity. During exercise and recovery of 20 min after exercise, esophageal temperature (Tes), mean skin temperature, mean body temperature ( ), chest sweating rate ( ), and the frequency of sweat expulsion (F _SW) were measured. In both experiments, andF _SW were clearly higher during exercise than recovery at a similar body temperature (Tes, ). was similar during exercise and recovery, or a little less during the former, at a similarF _SW. It is concluded that the sweating rate during exercise is greater than that during recovery at the same body temperature, due to greater central sudomotor activity during exercise. The difference between the two values is thought to be related to non-thermal factors and the rate of change in mean skin temperature.     

Eingangs-ausgangsbeziehungen und modell eines drehreflexes der haustaubeColumbia livia

Pigeons sitting on a turntable are exposed to horizontal -ramp-and-hold stimuli (= -RP-stimuli; angular velocity) (Fig. 1). At the same time, the mean rateE(t) of impulses/0.1 s or 0.2 s ofM. abductor indicis, M. abductor pollicis orM. flexor pollicis is registered. If the rotation axis lies in or in front of the pigeon's head the muscles studied respond phasic-tonicly to an ipsilaterad -RP-stimulus; and purely tonicly or also phasic-tonicly to a contralaterad -RP-stimulus (Figs. 2C and 4). The heightE _P of the tonic response component is independent from the direction of rotation and is only determined by the height of the -plateau (Fig. 2A). The heightE _D of the phasic response component is dependent upon the rotation direction and is determined, at a given rotation direction, by (Fig. 2A) and by the ramp slope ( angular acceleration) (Fig. 3A). This and the dependence of the tonic component and, with some pigeons, also of the phasic component uponr (distance between pigeon and rotation axis) lead to the conclusion that the tonic component is caused by the centripetal accelerationb _p , and the phasic component is caused by the angular acceleration and, with some pigeons, by the tangential accelerationb _t. The influence of the acceleration components uponE _D andE _P is dependent upon the pigeon's position angle relativ to the radiusvectorr (Figs. 4 and 5). The tonic component is the response to a quasi-pitch or a quasi-roll of the pigeon during steady rotation. This results from a comparison of the -RP-responses of the pigeon in a radial or tangential position (Fig. 6A) to the pitch and roll responses (Fig. 6B). A model has been developed on the basis of the measured stimulus-response relations (Fig. 7). It contains three input channels (x -,u _t- andu _p-channel) with low-pass filters for the angular, tangential and centripetal acceleration. The channel gain depends upon . The sum(t) of all channel outputs is sent through a pure-time-delay element and finally through a half-wave rectifier with a threshold and an upper limitation. The transfer characteristics of the model agree rather well with those of the pigeon. The model can be interpreted in terms of neurophysiology.

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Teil einer Habilitationsschrift an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität des Saarlandes.

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Herrn Prof. Dr. W. Nachtigall danke ich für die großzügige Unterstützung der Arbeit. Fräulein A. Jahner danke ich für die Assistenz und für die Anfertigung der Abbildungen, meiner Frau für die kritische Durchsicht des Textes. Frau Dr. M. Biederman-Thorson und Herrn Prof. Dr. D. Varjú bin ich für wertvolle Kritik dankbar. Die Arbeit wurde zum Teil aus Mitteln der Stiftung Volkswagenwerk finanziert, die Herm Prof. Dr. W. Nachtigall zur Verfügung standen.     

Energetics of the growth of Methanobacterium thermoautotrophicum and Methanococcus thermolithotrophicus on ammonium chloride and dinitrogen

Methanobacterium thermoautotrophicum was grown in continuous culture in a fermenter gassed with H₂ and CO₂ as sole carbon and energy sources, and in a medium which contained either NH₄Cl or gaseous N₂ as nitrogen source. Growth was possible with N₂. Steady states were obtained at various gas flow rates with NH₄Cl and with and the maintenance coefficient varied with the gas input and with the nitrogen source. Growth of Methanococcus thermolithotrophicus in continuous culture in a fermenter gassed with H₂, CO₂ as nitrogen, carbon and energy sources was also examined.Abbreviations molecular growth yield (g dry weight of cells per mol of CH₄ evolved) - growth rate (h^-1) - D dilution rate (h^-1) - rate (h_-1); relation of Neijssel and Tempest and of Stouthamer and Bettenhaussen - energy     

Cardiovascular responses to sustained maximal isometric contractions of the finger flexors

This study investigated cardiovascular responses to 2 min sustained submaximal (20% MVC) and maximal (100% MVC) voluntary isometric contractions of the finger flexors in healthy young women. Cardiovascular variables investigated were: heart rate (f _c), mean arterial pressure ( _a), and stroke volume (SV). Doppler echocardiography was used to estimate SV from measures of aortic diameter (AD) and time-velocity integrals. Preliminary studies indicated that AD did not change significantly after 2 min sustained 100% MVC. Therefore, pre-exercise AD values were used to calculate SV before, during and after exercise. During the 2-min 100% MVC period, f _c and _aincreased significantly during the first 30 s of contraction. f _c then remained constant during the remainder of the 2-min contraction period, while _acontinued to rise. SV did not change significantly during the 100% MVC task but increased significantly during recovery from sustained 100% MVC. The data suggest that the magnitude of cardiovascular responses to isometric exercise is dependent on the specific task performed, and that there is a different pattern of response for f _c, _a, and SV during 20% and 100% MVC tasks. Unlike f _c and _a, SV did not change significantly during isometric exercise, but increased significantly after sustained 100% MVC.     

Bacterial sodium ion-coupled energetics

For many bacteria Na⁺ bioenergetics is important as a link between exergonic and endergonic reactions in the membrane. This article focusses on two primary Na⁺ pumps in bacteria, the Na⁺-translocating oxaloacetate decarboxylase ofKlebsiella pneumoniae and the Na⁺-translocating F₁F₀ ATPase ofPropionigenium modestum. Oxaloacetate decarboxylase is an essential enzyme of the citrate fermentation pathway and has the additional function to conserve the free energy of decarboxylation by conversion into a Na⁺ gradient. Oxaloacetate decarboxylase is composed of three different subunits and the related methylmalonyl-CoA decarboxylase consists of five different subunits. The genes encoding these enzymes have been cloned and sequenced. Remarkable are large areas of complete sequence identity in the integral membrane-bound -subunits including two conserved aspartates that may be important for Na⁺ translocation. The coupling ratio of the decarboxylase Na⁺ pumps depended on and decreased from two to zero Na⁺ uptake per decarboxylation event as increased from zero to the steady state level.InP. modestum, is generated in the course of succinate fermentation to propionate and CO₂. This is used by a unique Na⁺-translocating F₁F₀ ATPase for ATP synthesis. The enzyme is related to H⁺-translocating F₁F₀ ATPases. The F₀ part is entirely responsible for the coupling of ion specificity. A hybrid ATPase formed by in vivo complementation of anEscherichia coli deletion mutant was completely functional as a Na⁺-ATP synthase conferring theE. coli strain the ability of Na⁺-dependent growth on succinate. The hybrid consisted of subunits a, c, b, and part of fromP. modestum and of the remaining subunits fromE. coli. Studies on Na⁺ translocation through the F₀ part of theP. modestum ATPase revealed typical transporter-like properties. Sodium ions specifically protected the ATPase from the modification of glutamate-65 in subunit c by dicyclohexylcarbodiimide in a pH-dependent manner indicating that the Na⁺ binding site is at this highly conserved acidic amino acid residue of subunit c within the middle of the membrane.     

Transport of H+, K+, Na+ and Ca++ in Streptococcus

Summary The streptococci differ from other bacteria in that cation translocations (with the possible exception of one of the K⁺ uptake systems) occur by primary transport systems, i.e., by cation pumps which use directly the free energy released during hydrolysis of chemical bonds to power transport. Transport systems in other bacteria, especially for Na⁺ and Ca⁺⁺, are often secondary, using the free energy of another ion gradient to drive cation transport. In streptococci H⁺ efflux occurs via the F₁F₀-ATPase. This enzyme is composed of eight distinct subunits. Three of the subunits are embedded in the membrane and form a H⁺ channel; this is called the F₀ portion of the enzyme. The other five subunits form the catalytic part of the enzyme, called F₁, which faces the cytoplasm and can easily be stripped from the membrane. Physiologically, this enzyme functions as a H⁺-ATPase, pumping protons out of the cell to form an electrochemical proton gradient, . The F₁F₀-ATPase, however, is fully reversible and if supplied with P_i, ADP and a + of sufficient magnitude (ca –200 mv) catalyzes the synthesis of ATP. Streptococcus faecalis can accumulate K⁺ and establish a gradient of 50 000:1 (in>out) under some conditions. Uptake occurs by two transport systems. The dominant, constitutive system requires both an electrochemical proton gradient and ATP to operate. The minor, inducible K⁺ transport system, which has many similarities to the K⁺-ATPase of the Kdp transport system found in Escherichia coli, requires only ATP to power K⁺ uptake.Sodium extrusion occurs by a Na⁺/H⁺-ATPase. Exchange is electroneutral and there is no requirement for a . The possibility that the Na⁺/H⁺-ATPase may consist of two parts, a catalytic subunit and a Na⁺/H⁺ antiport subunit, is suggested by the finding that damage to the Na⁺ transport system either through mutation or protease action leads to the appearance of -requiring Na⁺/H⁺ antiporter activity.Ca⁺⁺ like Na⁺ is extruded from metabolizing, intact cells. Transport requires no but does require ATP. Reconstitution of Ca⁺⁺ transport activity with accompanying Ca⁺⁺-stimulated ATPase activity into proteoliposomes suggests that Ca⁺⁺ is transported by a Ca⁺⁺-translocating ATPase.Where respiring organelles and bacteria use secondary transport systems the streptococci have developed cation pumps. The streptococci, which are predominantly glycolyzing bacteria, generate a much inferior to that of respiring organisms and organelles. The cation pumps may have developed simply in response to an inadequate .Abbreviations electrochemical potential of protons - membrane potential - pH pH gradient - p proton-motive force - DCCD N,Na¹-dicyclohexlcarbodiimide - TCS tetrachlorosalicylanilide - FCCP carbonylcyanide-p-trifluoromethylphenylhydrazone - CCCP carbonylcyanie-m-chlorophenylhydrazone - TPMP⁺ triphenylmethyl phosphonium ion - DDA⁺ dibenzyldimethylammonium ion - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - EGTA ethyleneglycol-bis (amino-ethyl-ether)-N,N-tetraacetic acid     

Cardiovascular responses to facial cooling during low and moderate intensity exercise

To investigate the hypothesis that facial cooling (FC) exerts a greater influence on the cardiovascular system at lower versus higher levels of exercise, this study examined the effect of facial cooling [mean (SE): 0 (2)°C at 0.8 m·s^–1 wind velocity] during 30 min low [35% maximum oxygen consumption ( O_2max)] and moderate (70% O_2max) levels of cycle ergometry in the supine position. Five male subjects were assigned in random order to four exercise conditions: (1) FC at 35% O_2max(FC35), (2) no cooling (NFC35), (3) FC at 70% O_2max(FC70), and (4) no cooling (NFC70). Heart rate (f _c), stroke volume (V _s), and cardiac output ( _c) were measured at rest and every 10 min of exercise using impedance cardiography. During FC35, the change in f _c [mean (SE)] was significantly lower (P < 0.05) than NFC35 at 10 [22 (5) vs 31 (3) beats· min^–1], 20 [29 (6) vs 35 (3) beats·min^–1], and 30 [29 (5) vs 38 (4) beats·min^–1] min. No differences in f _c were observed between FC70 and NFC70. Furthermore, FC had no effect on V _s or _cat either exercise intensity. However, when comparing the FC70 and NFC70 conditions, there was a significant main effect (P<0.05) in mean arterial pressure (P _a) response with cooling despite the fact that neither V _s or _cwere different from the NFC70 control. The increase (P < 0.05) in the estimated change in systemic vascular resistance ( _a· _c ^–1) could partly explain the relative rise in _aat FC70. No pressor effect of cooling was observed at 35% O_2max. The results suggest that the FC condition promotes exercise bradycardia at low levels of exercise and exerts a greater pressor response during moderate exercise.     

Pace of diffusion through membranes

Summary Although membranes are often viewed as barriers to diffusing particles, in many cases their presence does not slow down diffusion. Investigations of the transit time (mean diffusion time) for cases where the source and the target of diffusing particles are separated by various arrangements of membranes reveal the following facts: (i) The transit time is composed of the sum of the times to diffuse each of the membrane and aqueous regions separately and terms representing the time spent at the vicinity of the interfaces between these regions. (ii) In cases of one dimensional diffusion between aqueous and membranal phases, the transit time is governed by the parameter whereD _m andD _w are the diffusion coefficients in the membrane and water, respectively, and is the membrane/water partition coefficient of the particles. While the former ratio depends mostly on the viscosities of the two phases, the latter parameter is very strongly dependent on the identity of the particles. The diffusion from water to the membrane is faster than from the membrane to water whenever 1$$ " align="middle" border="0"> . The opposite is true when this parameter is smaller than 1. (iii) In case of one dimensional transmembranal diffusion, the transit time shows a minimum when wherel _w1 andl _w2 are the net diffusion distances in the aqueous phases on both sides of the membrane. In this case, if the diffusion proceeds through pores in the membrane, represents the fraction of membrane area that is occupied by the pores.The transit times for three dimensional diffusion into and from a spherical cell are also presented in a simple form. In addition, some of the relations between transit times and other measurable time parameters, such as the course of the decay of gradients and the time lag to establish steady states, are discussed briefly.The conclusions emerging from this analysis, together with the simple expressions for the transit times can make these investigation useful for the understanding of diffusion in systems containing natural or artificial membranes.