The influence of external potassium on the inactivation of sodium currents in the giant axon of the squid, Loligo pealei

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na⁺ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of h _∞, τ_h, α_h,and β_h as functions of membrane potential were determined for various [K _o]. The steady-state values of the h parameter were found to be inversely related, while the time constant, τ_h, was directly related to external K⁺ concentration. While the absolute magnitude as well as the slopes of the h _∞ vs. membrane potential curves were altered by varying external K⁺, only the magnitude and not the shape of the corresponding τ_h curves was altered. Values of the two rate constants, α_h and β_h, were calculated from h_∞ and τ_h values. α_h is inversely related to [K_o] while β_h is directly related to [K_o] for hyperpolarizing membrane potentials and is independent of [K_o] for depolarizing membrane potentials. Hodgkin-Huxley equations relating α_h and β_h to E_m were rewritten so as to account for the observed effects of [K_o]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.     

Effects of plant growth regulators on Hill activity of submerged aquatic plants during induced senescence

Effects of plant growth regulators on Hill activity during induced senescence of leaves of three submerged aquatic plants Vallisneria spiralis L., Hydrilla verticillata (L.f.) Royle and Potamogeton pectinatus L., and a terrestrial plant Spinacia oleracea L. were studied. Hill activity was reduced by 39.3, 42.7, 45.2 and 245.1 μmol DCIP (2,6-dichloroindophenol) (mg chl)^?1h^?1 in Vallisneria, Hydrilla, Potamogeton and Spinacia, respectively. During induced senescence of isolated mature leaves, Hill activity declined with increasing incubation time in all species. Kinetin (0.23 mM) treatment reduced the loss of Hill activity; while both 0.69 mM ehthrel and 0.075 mM ABA treatments decreased it in each species. The effect of kinetin was greatest in Spinacia, followed by Potamogeton, Hydrilla and Vallisneria, while the effect of either ethrel or ABA or both was greatest in Potamogeton, followed by Spinacia, Vallisneria and Hydrilla. Kinetin pre-treatment for an optimal period (12 h) followed by treatment with either ethrel or ABA partially removed the inhibitory effect of the latter on Hill activity. Pre-treatment of tissues with either ethrel or ABA solution, restricted to 12 h, followed by kinetin treatment markedly reduced the promotive effect of kinetin on the Hill activity of these species.     

Inhibition kinetics of a commercial mixed culture by ammonium sulfate

The inhibitory effect of ammonium sulfate on a commercial mixed culture, used in biological waste-water treatment was studied under aerobic batch conditions. Several mathematical models of enzyme and growth kinetics including a death factor were analyzed through nonlinear regression to find the best fit to corresponding data of inhibition. The best fit model was found to be the generalized Monod type with a death factor having the biokinetic parameters; μ_max 0.681 h⁻¹, K_s 0.224 g dm⁻³, K_i 56240 g dm⁻³, K 0.055 g dm⁻³ and k_d 0.052 h⁻¹ to represent the experimental data accurately. The low saturation coefficient value along with high maximum specific growth rate and inhibition coefficient denotes the competitive characteristics of commercial mixed cultures in the biological treatment of high ammonium polluted waste waters.     

A Novel Method for Measuring the Diffusion,Partition and Convective Mass Transfer Coefficients of Formaldehyde and VOC in Building Materials

The diffusion coefficient (D _m) and material/air partition coefficient (K) are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC) sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (h _m). Compared to traditional methods, it has the following merits: (1) the K, D _m and h _m can be simultaneously obtained, thus is convenient to use; (2) it is time-saving, just one sorption process in airtight chamber is required; (3) the determination of h _m is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring h _m of semi-volatile organic compounds (SVOC) by using that of VOC.     

Regulation of the Hill reaction by cations and its abolishment by uncouplers

Concurrent measurements of P-700 turnover and the reduction of K₃Fe(CN)₆ revealed an identical relative quantum yield for both reactions in isolated pea chloroplasts as well as chloroplast particles from wild type Scenedesmus. On the other hand, chloroplast particles of wild type Scenedesmus showed the same relative quantum yield for the Hill reaction as those of the P-700-free mutant No. 8, indicating that P-700 is not required for ferricyanide reduction.Several metal ions, such as Mg²⁺, Ca²⁺, Na⁺ and K⁺ stimulated the reduction of K₃Fe(CN)₆. In short wavelength light, the stimulation was a function of light intensity, varying in magnitude from an approximate doubling of the yield in low intensities to only a slight increase at light saturation. P-700 was totally unaffected by the cations.The effect of the metal salts was abolished in the presence of uncouplers of photophosphorylation.The data reconcile several divergent results concerning the effect of divalent cations on the reduction of ferricyanide which have been reported in the recent literature. On the whole the experiments suggest that the Hill acceptor can be reduced at two sites. The stimulation of the Hill reaction by metal ions is proposed to be due to an activation of Photosystem II and a more efficient utilization of quanta at the expense of radiationless de-excitation.     

Kinetics of Denitrifying Growth by Fast-Growing Cowpea Rhizobia

Two fast-growing strains of cowpea rhizobia (A26 and A28) were found to grow anaerobically at the expense of NO₃⁻, NO₂⁻, and N₂O as terminal electron acceptors. The two major differences between aerobic and denitrifying growth were lower yield coefficients (Y) and higher saturation constants (K_s) with nitrogenous oxides as electron acceptors. When grown aerobically, A26 and A28 adhered to Monod kinetics, respectively, as follows: K_s, 3.4 and 3.8 μM; Y, 16.0 and 14.0 g · cells eq⁻¹; μ_max, 0.41 and 0.33 h⁻¹. Yield coefficients for denitrifying growth ranged from 40 to 70% of those for aerobic growth. Only A26 adhered to Monod kinetics with respect to growth on all three nitrogenous oxides. The apparent K_s values were 41, 270, and 460 μM for nitrous oxide, nitrate, and nitrite, respectively; the K_s for A28 grown on nitrate was 250 μM. The results are kinetically and thermodynamically consistent in explaining why O₂ is the preferred electron acceptor. Although no definitive conclusions could be drawn regarding preferential utilization of nitrogenous oxides, nitrite was inhibitory to both strains and effected slower growth. However, growth rates were identical (μ_max, 0.41 h⁻¹) when A26 was grown with either O₂ or NO₃⁻ as an electron acceptor and were only slightly reduced when A28 was grown with NO₃⁻ (0.25 h⁻¹) as opposed to O₂ (0.33 h⁻¹).     

Soybeans and radish leaves contain only one of the sulfonium diastereoisomers of S-adenosylmethionine

Using a liquid chromatography method that separates the two sulfonium diastereoisomers of adenosylmethionine, we have found that immature soybeans, soybean callus culture, radish leaves, yeast and rat liver contain only the (S)-sulfonium form of S-adenosylmethionine. Our findings contradict the suggestion by Stolowitz and Minch that 10–20% of naturally-occurring adenosylmethionine may have the (R)-configuration at the sulfonium pole. Absence of the (R)-sulfonium isomer of adenosylmethionine in biological materials indicates that the (R)-sulfonium form of adenosylmethionine present in commercial adenosylmethionine samples is an artifact of the isolation procedure. Our method of measuring the isomers of adenosylmethionine enabled us to readily determine the rate of racemization and hydrolysis of adenosylmethionine. Our rate constants for racemization (K_r) and hydrolysis (K_h) were 2.4 × 10^?6 sec^?1 and 12.3 × 10-^?6 sec^?1, respectively; values which are noticeably different from those of Wu and co-workers which were obtained with a more complicated method (K_r = 8 × 10^?1 sec^?1; K_h = 6 × 10^?6 sec^?1). We believe the absence of the (R)-isomer in vivo is best explained by stabilization of the (S)-isomer as suggested by Wu et al. Although the tissues we have analysed contained the (S)-sulfonium form of adenosylmethionine exclusively, when ethionine-resistant soybean cell lines were given ethionine, they accumulated both sulfonium diastereoisomers of adenosylethionine.     

Genetic noise control via protein oligomerization

Background

Biochemical equilibria are usually modeled iteratively: given one or a few fitted models, if there is a lack of fit or over fitting, a new model with additional or fewer parameters is then fitted, and the process is repeated. The problem with this approach is that different analysts can propose and select different models and thus extract different binding parameter estimates from the same data. An alternative is to first generate a comprehensive standardized list of plausible models, and to then fit them exhaustively, or semi-exhaustively.

Results

A framework is presented in which equilibriums are modeled as pairs (g, h) where g = 0 maps total reactant concentrations (system inputs) into free reactant concentrations (system states) which h then maps into expected values of measurements (system outputs). By letting dissociation constants K _d be either freely estimated, infinity, zero, or equal to other K _d , and by letting undamaged protein fractions be either freely estimated or 1, many g models are formed. A standard space of g models for ligand-induced protein dimerization equilibria is given. Coupled to an h model, the resulting (g, h) were fitted to dTTP induced R1 dimerization data (R1 is the large subunit of ribonucleotide reductase). Models with the fewest parameters were fitted first. Thereafter, upon fitting a batch, the next batch of models (with one more parameter) was fitted only if the current batch yielded a model that was better (based on the Akaike Information Criterion) than the best model in the previous batch (with one less parameter). Within batches models were fitted in parallel. This semi-exhaustive approach yielded the same best models as an exhaustive model space fit, but in approximately one-fifth the time.

Conclusion

Comprehensive model space based biochemical equilibrium model selection methods are realizable. Their significance to systems biology as mappings of data into mathematical models warrants their development.     

The Coefficient of Thermal Conductivity of Blood and of Various Tissues

A method for measuring K, the coefficient of thermal conductivity, for a variety of dog tissues is described. The values of K for muscle and liver are larger than that for water, the value of K for lung is smaller than that for water and the values of K for brain, plasma, and blood are about the same as that of water. The values found for K are given in a table.     

Hydrolysis of adenylyl imidodiphosphate in the presence of Na+ + Mg+ by (Na+ + K+)-activated ATPase

(1) Contrary to what has usually been assumed, (Na⁺ + K⁺)-ATPase slowly hydrolyses AdoPP[NH]P in the presence of Na⁺ + Mg²⁺ to ADP-NH₂ and P_i. The activity is ouabain-sensitive and is not detected in the absence of either Mg²⁺ or Na²⁺. The specific activity of the Na⁺ + Mg²⁺ dependent AdoPP[NH]P hydrolysis at 37°C and pH 7.0 is 4% of that for ATP under identical conditions and only 0.07% of that for ATP in the presence of K⁺. The activity is not stimulated by K⁺, nor can K⁺ replace Na⁺ in its stimulatory action. This suggests that phosphorylation is rate-limiting. Stimulation by Na⁺ is positively cooperative with a Hill coefficient of 2.4; half-maximal stimulation occurs at 5–9 mM. The K_m value for AdoPP[NH]P is 17 μM. At 0°C and 21°C the specific activity is 2 and 14%, respectively, of that at 37°C. AMP, ADP and AdoPP[CH₂]P are not detectably hydrolysed by (Na⁺ + K⁺)-ATPase in the presence of Na⁺ + Mg²⁺. (2) In addition, AdoPP[NH]P undergoes spontaneous, non-enzymatic hydrolysis at pH 7.0 with rate constants at 0, 21 and 37°C of 0.0006, 0.006 and 0.07 h^?1, respectively. This effect is small compared to the effect of enzymatic hydrolysis under comparable conditions. Mg²⁺ present in excess of AdoPP[NH]P reduces the rate constant of the spontaneous hydrolysis to 0.005 h^?1 at 37°C, indicating that the MgAdoPP[NH]P complex is virtually stable to spontaneous hydrolysis, as is also the case for its enzymatic hydrolysis. (3) A practical consequence of these findings is that AdoPP[NH]P binding studies in the presence of Na⁺ + Mg²⁺ with enzyme concentrations in the mg/ml range are not possible at temperatures above 0°C. On the other hand, determination of affinity in the (Na⁺ + K⁺)-ATPase reaction by competition with ATP at low protein concentrations (μg/ml range) remains possible without significant hydrolysis of AdoPP[NH]P even at 37°C.     

Yield and kinetic constants estimation in the production of hydroxy fatty acids from oleic acid in a bioreactor by Pseudomonas aeruginosa 42A2

We modelled the production of hydroxy fatty acids from oleic acid by Pseudomonas aeruginosa 42A2 in a bioreactor with a non-dispersive aeration system. First, we designed an adapted wetted-wall gas-absorption column, offering a k _La value of 39.9 h^?1, to enhance oxygen absorption in the culture media and prevent foam formation. Then, we analysed different kinetic models to simulate the yield coefficients and the kinetic constants in this bacterial transformation. Monod model fitting (μ _max1?=?0.51 h^?1, K _S1?=?1.60 C-mol l^?1, μ _max2?=?0.12 h^?1, K _S2?=?0.035 C-mol l^?1, and k ₂?=?0.033 h^?1) showed a good accuracy with the experimental data sets and was chosen for its simplicity. Lastly, mass balances were carried out to establish the stoichiometry of this biotransformation with the following yield coefficients, Υ _X/OA, Υ _{X/(10S)-HPOME} and Υ _{(10S)-HPOME/(7S10S)-HPOME} of 0.172, 0.347 and 2.388 C-mol C-mol^?1, respectively.     

Effect of oxygen supply on biomass and helvolic acid production in submerged fermentation of Cordyceps taii

The entomogenous fungus Cordyceps taii, a traditional Chinese medicinal mushroom, exhibits potent important pharmacological effects and it has great potential for health foods and medicine. In this work, the effects of oxygen supply on production of biomass and bioactive helvolic acid were studied in shake-flask fermentation of C. taii mycelia. The value of initial volumetric oxygen transfer coefficient (K_La) within 10.1–33.8 h⁻¹ affected the cell growth, helvolic acid production and expression levels of biosynthetic genes. The highest cell concentration of 17.2 g/L was obtained at 14.3 h⁻¹ of initial K_La. The highest helvolic acid production was 9.6 mg/L at 10.1 h⁻¹ of initial K_La. The expression levels of three genes encoding hydroxymethylglutaryl-CoA synthase, hydroxymethylglutaryl-CoA reductase and squalene synthase were down-regulated on day 2 and day 8 but up-regulated on day 14 at an initial K_La value of 10.1 h⁻¹ vs. 33.8 h⁻¹, which well corresponded to the helvolic acid biosynthesis in those conditions. The information obtained would be helpful for improving the biomass and helvolic acid production in large-scale fermentation of C. taii.     

Determination of enzyme kinetic parameters by continuous addition of substrate to a single reaction mixture and analysis by a tangent-slope procedure: I. Analysis of the method using computed progress curves

A new method has been developed which provides reliable estimates of enzyme kinetic constants from single reaction progress curves recorded under conditions of continuously increasing substrate concentration. Equally spaced data points simulating such progress curves and containing known amounts of superimposed random noise were fit to the Hill equation by (i) direct nonlinear curve-fitting of raw data, and (ii) a tangent-slope technique in which the raw data are numerically differentiated, transformed into substrate versus velocity data, and then analyzed as linear plots. Both integral and differential procedures provided accurate and precise estimates of the Hill parameters (S_0.5, V, and n) from single reaction mixtures. However, the tangent-slope method was at least 10-fold faster to compute and was not dependent on accurate initial guesses of the Hill parameters or integration of the rate equation. With the tangent-slope method, the optimal number of data points used in calculating tangent slopes was found to be 9 or 11. The reliability of the Hill parameters determined with the tangent-slope method was relatively insensitive to the maximum substrate concentration over a range of $\text{S}{}_{\mathrm{<mtext>max</mtext>}}\text{S}{}_{0.5}$ of 1.5 to 10; the optimal value was 3. Through further analysis of simulated data, it was found that slow enzyme inactivation (<4% loss during the assay), or product competitive inhibition (maximum product concentration < 30% of the inhibitor dissociation constant) does not produce serious errors in the Hill parameters. Methods are presented to detect and distinguish enzyme inactivation and product competitive inhibition. It is suggested that continuous addition methodology combined with tangent-slope analysis provides the basis for a flexible system for kinetic characterization of enzymes which has wider applicability and other advantages over multicuvette or conventional progress curve methodology. A major advantage in contrast to the progress curve approach is that product accumulation and associated product effects are lowest at lower substrate concentrations.     

Kinetics study of pyridine biodegradation by a novel bacterial strain,Rhizobium sp. NJUST18

Biodegradation of pyridine by a novel bacterial strain, Rhizobium sp. NJUST18, was studied in batch experiments over a wide concentration range (from 100 to 1,000 mg l^?1). Pyridine inhibited both growth of Rhizobium sp. NJUST18 and biodegradation of pyridine. The Haldane model could be fitted to the growth kinetics data well with the kinetic constants μ* = 0.1473 h^?1, K _s = 793.97 mg l^?1, K _i = 268.60 mg l^?1 and S _m = 461.80 mg l^?1. The true μ _max, calculated from μ*, was found to be 0.0332 h^?1. Yield coefficient Y _X/S depended on S _i and reached a maximum of 0.51 g g^?1 at S _i of 600 mg l^?1. V _max was calculated by fitting the pyridine consumption data with the Gompertz model. V _max increased with initial pyridine concentration up to 14.809 mg l^?1 h^?1. The q _S values, calculated from $V_{ \hbox{max} }$ , were fitted with the Haldane equation, yielding q _Smax = 0.1212 g g^?1 h^?1 and q* = 0.3874 g g^?1 h^?1 at S _m′ = 507.83 mg l^?1, K _s′ = 558.03 mg l^?1, and K _i′ = 462.15 mg l^?1. Inhibition constants for growth and degradation rate value were in the same range. Compared with other pyridine degraders, μ _max and S _m obtained for Rhizobium sp. NJUST18 were relatively high. High K _i and K _i′ values and extremely high K _s and K _s′ values indicated that NJUST18 was able to grow on pyridine within a wide concentration range, especially at relatively high concentrations.     

Nutrient uptake rates by the alien alga Undaria pinnatifida (Phaeophyta) (Nuevo Gulf, Patagonia, Argentina) when exposed to diluted sewage effluent

In the early nineties, Undaria pinnatifida has been accidentally introduced to Nuevo Gulf (Patagonia, Argentina) where the environmental conditions would have favored its expansion. The effect of the secondary treated sewage discharge from Puerto Madryn city into Nueva Bay (located in the western extreme of Nuevo Gulf) is one of the probable factors to be taken into account. Laboratory cultures of this macroalgae were conducted in seawater enriched with the effluent. The nutrients (ammonium, nitrate and phosphate) uptake kinetics was studied at constant temperature and radiation (16?°C and 50 μE m^?2 s^?1 respectively). Uptake kinetics of both inorganic forms of nitrogen were described by the Michaelis–Menten model during the surge phase (ammonium: V _max ^sur: 218.1 μmol h^?1 g^?1, K _s ^sur: 476.5 μM and nitrate V _max ^sur: 10.7 μmol h^?1 g^?1, K _s ^sur: 6.1 μM) and during the assimilation phase (ammonium: V _max ^ass: 135.6 μmol h^?1 g^?1, K _s ^ass: 407.2 μM and nitrate V _max ^ass: 1.9 μmol h^?1 g^?1, K _s ^ass: 2.2 μM), with ammonium rates always higher than those of nitrate. Even though a net phosphate disappearance was observed in all treatments, uptake kinetics of this ion could not be properly estimated by the employed methodology.     

Multifractal analysis of K+ channel activity

The Multifractal version of the Detrended Fluctuation Analysis was used for the study of non-stationary dwell time series of Ca²⁺-activated K⁺ channels (K_Ca channels) in cultured kidney Vero cells and of voltage-dependent K⁺ channels (K_v channels) in mollusc (Lymnaea stagnalis) neurons. The data obtained can briefly be summarized as follows: (i) The generalized fluctuation function F _q (l) strongly depends on the index (order) q; for monofractal time series, such dependence is nonexistent; (ii) The relationship between the scaling exponent τ commonly employed in standard multifractal analysis and q is characterized by two slopes and a transitory region, whereas monofractal processes are characterized by the linear dependence; (iii) The relationship between the singularity spectrum f(h) and the Hurst exponent h is bell-shaped, while in the case of monofractal processes it is represented by a single point f(h) = 1. Random mixing of the time series resulted in the narrowing of the spectrum f(h) and a shift of f(h) towards the value more characteristic of stochastic (monofractal) processes (h ～ 0.5). It is concluded that the activities of both K_Ca channels in kidney Vero cells and of K_V channels in mollusc (Lymnaea stagnalis) neurons can be characterized as multifractal processes.     

The mode of activation by potassium of potassium-dependent and ouabain-sensitive phosphatase activity.

A new simple procedure has been developed for the purification of plasma membranes from rabbit kidney microsomes which yields a three- to fourfold increase in the specific activity of Na⁺-K⁺-adenosine triphosphatase (ATPase). The procedure differs from previous methods with deoxycholate or other detergents and does not change the molecular activity of the ATPase. The K⁺-dependent p-nitrophenylphosphatase activity of the native Na⁺-K⁺-ATPase is controlled more effectively by Mg²⁺ in the presence of K⁺ at concentrations higher than that of Mg²⁺, and by K⁺ in the presence of Mg²⁺ at concentrations higher than that of K⁺. The enzyme in its Mg²⁺-regulating state, which shows K⁺-saturation curves with a Hill coefficient of 1, is less sensitive to ouabain (I_0.5 = 90 μM) and corresponds to the enzyme conformation reported previously which is inhibited by the concurrent presence of Na⁺ and ATP or of Na⁺ and oligomycin (I_0.5 is the midpoint of the saturation curve). The enzyme in its K⁺-regulating state, which shows K⁺-saturation curves with a Hill coefficient of 2, is more sensitive to ouabain inhibition (I₀₅ = 8 μM) and corresponds to the enzyme conformation which is stimulated by the concurrent presence of Na⁺ and ATP or of Na⁺ and oligomycin. There appear to be two conformations of the enzyme that are regulated by Mg²⁺ binding on the inhibitory sites of the enzyme.     

Degradation of poly(adenosine diphosphate ribose) by homogenates of various normal tissues and tumors of rats.

The extent of increase in the activity of phenylalanine ammonia-lyase upon illumination for 15 hr of cultured Petroselinum hortense cells was greatly dependent upon the age of the culture. Two distinct peaks in specific activity were observed during the growth cycle, one occurring at the beginning and the other at the end of the period of increase in cell fresh weight. High yields in both cell fresh weight and enzyme activity were obtained with the second peak shortly before the stationary phase of the culture was reached. Cells were harvested at this stage and stored at ?20 °C.The enzyme was purified from the frozen cells to apparent homogeneity by precipitation with (NH₄)₂SO₄, chromatography on DEAE-cellulose, Sephadex G-200 and hydroxyapatite columns, and preparative polyacrylamide gel electrophoresis. An over-all yield of 16% was achieved with a 440-fold increase in the specific activity by purification of the enzyme through the hydroxyapatite step.Upon analytical polyacrylamide gel electrophoresis either in the presence or in the absence of sodium dodecyl sulfate, the purified protein migrated essentially as a single band. Molecular weights of about 330,000 and 83,000, respectively, were estimated for the enzyme and for its protein subunits. Thus, the enzyme molecule seems to be composed of four probably identical protein subunits. Two Michaelis constants for l-phenylalanine (K_m^L, 3.2 × 10^?5 M, and K_m^H, 2.4 × 10^?4 M) and a Hill coefficient of h = 0.6 were obtained. This suggests that the enzyme is subject to regulation of its catalytic properties by negative cooperativity of the protein subunits.     

Effects of dehydration and low temperatures on the oxidation of high-potential cytochrome c by photosynthetic reaction centers in Ectothiorhodospira shaposhnikovii

Effects of temperature and dehydration on the efficiency of electron transfer from membrane-bound high-potential cytochromes c_h to the reaction-center bacteriochlorophyll (P-890) in Ectothiorhodospira shaposhnikovii have been studied. A kinetic analysis of the cytochrome oxidation suggests that there are at least two conformational states of the c_h-P-890 complex, of which only one allows photoinduced electron transfer from cytochrome to P-890⁺. Lowering the temperature of dehydration leads to a change in the proportion of the populations in the two conformations. The observed 2-fold deceleration of cytochrome oxidation can be related only to the diminution of the amount of photoactive cytochromes per reaction center. The rate constant for the transfer of an electron from cytochrome c_h to bacteriochlorophyll is 2.8 · 10⁵ s⁻¹ and is independent of temperature and dehydration (as estimated within the accuracy of the experiments). The effects produced by low temperature and dehydration are completely reversible. The thermodynamic parameters of the transition of the cytochrome from the nontransfer to electron-transfer conformation were estimated. For room temperature (+ 20°C) in chromatophore preparations, ΔG = −5.4 kJ · M⁻¹, ΔH = 60 kJ · M⁻¹, ΔS = 0.22 kJ · M⁻¹ · K⁻¹. For Triton X-100 subchromatophore preparations, the absolute values of the above parameters are significantly lower: ΔG = −2.8 kJ · M⁻¹, ΔH = 18 kJ · M⁻¹, and ΔS = 0.075 kJ · M⁻¹ · K⁻¹. To a larger extent, the above parameters are diminished for chromatophore preparations in an 80% glycerol solution: ΔG = −1.7 kJ · M⁻¹, ΔH = 6 kJ · M⁻¹, ΔS = 0.025 kJ · M⁻¹ · K⁻¹. The data suggest the hydrophobic character of the forces that maintain the P-890-c_h complex in the electron-transfer conformation. The results obtained suggest that electron tunneling within the complex cannot occur until a specific conformational configuration of the complex is formed. The efficiency of cytochrome c_h oxidation is determined by the temperature, the degree of dehydration and the environmental conditions, whereas the transfer of an electron itself in the electron-transfer configuration is essentially independent of temperature and hydration.