Temperature dependence of N-phenyl-1-naphthylamine binding in egg lecithin vesicles

The temperature dependence of the binding of PhNapNH₂ ($\text{N-}\text{phenyl-1-naphthylamine}$) to vesicles of egg phosphatidylcholine has been determined. The Arrhenius plot of the association constant exhibits a discontinuity at 20.9 °C, some 30 °C above the broad phase transition region of the phospholipid. In the temperature range above 20 °C, $\text{ΔH}{}^0\text{= ?6100}\text{cal·mol}{}^{\mathrm{?1}}$ and $\text{ΔS}{}^0\text{= 9.7}\text{e. u.}$; in the temperature range below 20 °C, $\text{ΔH}{}^0\text{= 0}\text{cal · mol}{}^{\mathrm{?1}}$ and $\text{ΔS}{}^0\text{= 30.4}\text{e. u.}$ These values are consistent with the view that there are well ordered lipid-lipid bonds below 20 °C which are significantly less important above this temperature. The order in the temperature range of 5 to 20 °C, though significantly greater than that above 20 °C, is still significantly less than that in the crystalline state.     

Acid dissociation of cyclohexaamylose and cycloheptaamylose

Acid dissociation constants of aqueous cyclohexaamylose (6-Cy) and cycloheptaamylose (7-Cy) have been determined at 10–47 and 25–55°C, respectively, by pH potentiometry. Standard enthalpies and entropies of dissociation derived from the temperature dependences of these pK_a's are ΔH⁰ = 8.4 ± 0.3 kcal mol^?1, $\text{Δ}\text{S}{}^0\text{= ?28. ± 1}\text{cal mol}{}^{\mathrm{?1}}{}^0\text{K}{}^{\mathrm{?1}}$ for 6-Cy and ΔH⁰ = 10.0 ± 0.1 kcal mol^?1, $\text{Δ}\text{S}{}^0\text{= ?22.4 ±0.3}\text{cal mol}{}^{\mathrm{?1}}{}^0\text{K}{}^{\mathrm{?1}}$ for 7-Cy. Intrinsic ¹³C nmr resonance displacements of anionic 6- and 7-Cy were measured at 30°C in 5% D₂O ($\text{v}\text{v}$). These results indicate that the dissociation of 6- and 7-Cy involves both C2 and C3 2⁰-hydroxyl groups. The thermodynamic and nmr parameters are discussed in terms of interglucosyl hydrogen bonding.     

Calorimetric investigations of the helix-coil conversion of phenylalaninespecific transfer ribonucleic acid

The enthalpy of the helix-coil conversion of phenylalaninespecific transfer ribonucleic acid from brewer's yeast (tRNA^Phe_{brewer's yeast}) has been measured using both an LKB 10700-2 batch miciocalorimeter and an adiabatic differential scanning calorimeter. In the mixing calorimeter the conversion from coil to helix was induced by mixing a tRNA^Phe solution with a solution containing an excess of MgSO₄. We measured the enthalpy of this reaction stepwise in the temperature range from +9 to +60° C. For the enthalpy of folding of tRNA^Phe from coil to helix this method yielded the remarkably high value of ?310 $\text{kcal}\text{mole}$ of tRNA^Phe. With the differential scanning calorimeter in which the helix-coil conversion is simply induced by raising the temperature we found a value of +240 $\text{kcal}\text{mole}$ of tRNA^Phe at a Tm value of 76° C and a value of +200 $\text{kcal}\text{mole}$ of tRNA^Phe at a T_m value of 50° C. A comparison of the apparent van't Hoff enthalpies with the calorimetrically measured enthalpies shows, that the cooperativity of the system increases continually with rising melting temperatures - which are achieved by increasing Mg²⁺ concentrations - reaching a constant value at about 57° C. Above this temperature value the thermodynamic behaviour of the helix-coil conversion of tRNA^Phe may be approximately described by the model of an all-or-none process.     

Lateral and transversal diffusion and phase transitions in erythrocyte membranes. An excimer fluorescence study

The lateral diffusion of the excimer-forming probe pyrene decanoic acid has been determined in erythrocyte membranes and in vesicles of the lipid extracts. The random walk of the probe molecules is characterized by their jump frequency, v_j, within the lipid matrix. At T = 35°C a value of v_j = 1.6 · 10³ s^?1 is found in erythrocyte membranes. A somewhat slower mobility is determined in vesicles prepared from lipid extracts of the erythrocyte membrane. Depending on structure and charge of the lipids we obtain jump frequencies between 0.8 · 10⁸ s^?1 and 1.5 · 10⁸ s^?1 at T = 35°C. The results are compared with jump frequencies yielded in model membranes.The mobility of molecules perpendicular to the membrane surface (transversal diffusion) is investigated. Erythrocyte ghosts doped with pyrene phosphatidylcholine were mixed with undoped ghosts in order to study the exchange kinetics of the probe molecule. A fast transfer between the outer layers of the ghost cells ($\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1.6}\text{min at}\text{T = 37°}\text{C}$) is found. The exchange process between the inner and the outer layer of one erythrocyte ghost (flip-flop process) following this fast transfer occurs with a half-life time value of $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 100}\text{min at}\text{T = 37°}\text{C}$.The application of excimer-forming probes presumes a fluid state of the membrane. Therefore we investigated the phase transition behaviour using the excimer technique. Beside a thermotropic phase transition at T = 23°C and T = 33°C we observed an additional fluidity change at T = 38°C in erythrocyte ghosts. This transition is attached to a separation of the boundary lipid layer from the intrinsic proteins. No lipid phase transition is observed in liposomes from isolated extracts of the erythrocyte membrane with our methods.     

A thermodynamic description of the self-association of flavin mononucleotide.

Systematic heat of dilution studies of the self-association of flavin mononucleotide (FMN) have been conducted as a function of ionic strength (0.05 – 2.0 m) and pH (5–9) in aqueous solution. The data are adequately described by the expression $\text{Q}{}_{\mathrm{T}}\text{= ΔH ? (}\text{ΔH}\text{K}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{Q}{}_{\mathrm{T}}\text{c}{}_{\mathrm{T}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for an isodesmic self-association. Q_T is the molar heat of dilution, ΔH and K are the derived enthalpy and equilibrium constants for the process FMN + (FMN)_i?1 ? (FMN)_i, and c_T is the concentration of FMN expressed in monomer units. Typical values derived for the various thermodynamic parameters at 25 °C are ΔG = ?3.56 kcal mol^?1, ΔH = ?3.72 kcal mol^?1, and ΔS = ?0.54 cal (mol · deg)^?1. These data, plus nuclear magnetic resonance evidence (Yagi, K., Ohishi, N., Takai, A., Kawano, K., and Kyogoku, Y., 1976, Biochemistry15, 2877–2880) argue in favor of an open-ended association of flavin molecules. The signs of the various thermodynamic parameters suggest that both hydrophobic and surface energy forces contribute significantly to the association, while the lack of any significant ionic strength dependence indicates the lack of any ionic centers in the association.     

Evaluation of the water environments in deoxygenated sickle cells by longitudinal and transverse water proton relaxation rates

The longitudinal and transverse water proton relaxation rates of oxygenated and deoxygenated erythrocytes from both normal adults and individuals with sickle cell disease were measured as a function of temperature at two different frequencies. The simplest model which fits all of the data consists of three different environments for water molecules. The majority of the water (98%) has a correlation time indistinguishable from bulk water (3 × 10^?11 sec). Secondly, there is a small amount of water (1.3–1.5%) present which has a correlation time of 2–4 × 10 ^?9 sec and is apparently independent of the erythrocyte sample studied. Presumably this water is the hydration sphere around the hemoglobin molecules and its correlation time is significantly slower than bulk water. The third environment contains approximately 0.2% of the water present and has a correlation time≥ 10^?7 sec. This third environment is considered tightly bound to the hemoglobin because the water proton correlation time is very similar to the expected rotational correlation time for the hemoglobin molecules. The value of the transverse relaxation rate, f_b(T_2b)^?1, for the tightly bound water fraction decreases in oxy ($\text{S}\text{S}$), deoxy ($\text{A}\text{A}$), and oxy ($\text{A}\text{A}$) erythrocyte samples as the temperature is increased as expected for a rotational correlation time process. In dramatic contrast,f_b (T_2b)^?1 increases almost linearly as the temperature is increased over the whole 4 ° to 37 °C temperature range in samples of deoxy ($\text{S}\text{S}$) erythrocytes. The observation suggests a continual increase in the formation of deoxyhemoglobulin S polymers rather than a sudden transition from a homogeneous solution of deoxyhemoglobin S molecules to a solid gel.     

Investigations on purine and pyrimidine bases stacking associations in aqueous solutions by the fluorescence quenching method: I. Autoassociation of 2-aminopurine

A general equation was derived, describing fluorescence quantum yield and lifetime of an autoassociating compound in liquid solutions. The autoassociation of 2-aminopurine in aqueous solution was examined within the range from 0 to 90°C. The compound seemed to associate cooperatively. The thermodynamic parameters of polymerization change with temperature, so that its free enthalpy ΔG = ?0.0797 T² + 45.4 T ?7893. The dimerization enthalpy and entropy are approximately temperature-independent (ΔH₂ = ?4.17 $\text{kcal}\text{mol}$, ΔS₂ = ?10.9 e.u.), although the function: ΔG₂ = ?0.0308 T² + 30.3 T - 7213 fits experimental points better. The observed dependences can be explained by the increasing role of the hydrophobic effect with temperature and size of the aggregates. The association rate constants were determined, and a two-step reaction mechanism was demonstrated. The first step is diffusion-controlled. The second is characterized by an activation energy of ~2 $\text{kcal}\text{mol}$ and an encounter distance of ~8.3 Å.     

Characterization of sodium and proton flows in sub-bacterial particles of Halobacterium halobium in terms of nonequilibrium thermodynamics

A thermodynamic characterization of the Na⁺-H⁺ exchange system in Halobacterium halobium was carried out by evaluating the relevant phenomenological parameters derived from potential-jump measurements. The experiments were performed with sub-bacterial particles devoid of the purple membrane, in 1 M NaCl, 2 M KCl, and at pH 6.5–7.0. Jumps in either pH or pNa were brought about in the external medium, at zero electric potential difference across the membrane, and the resulting relaxation kinetics of protons and sodium flows were measured. It was found that the relaxation kinetics of the proton flow caused by a pH-jump follow a single exponential decay, and that the relaxation kinetics of both the proton and the sodium flows caused by a pNa-jump also follow single exponential decay patterns. In addition, it was found that the decay constants for the proton flow caused by a pH-jump and a pNa-jump have the same numerical value. The physical meaning of the decay constants has been elucidated in terms of the phenomenological coefficients (mobilities) and the buffering capacities of the system. The phenomenological coefficients for the Na⁺-H⁺ flows were determined as differential quantities. The value obtained for the total proton permeability through the particle membrane via all available channels, $\text{L}{}_{\mathrm{<mtext>H</mtext>}}\text{= (}\text{?J}{}_{\mathrm{<mtext>H\; +</mtext>}}\text{?Δ}\text{pH}\text{)}{}_{\mathrm{<mtext>\Delta \psi ,\Delta </mtext><mtext>pNa</mtext>}}$, was in the range of 850–1150 nmol H⁺·(mg protein)^?1·h^?1·(pH unit)^?1 for four different preparations; for the total Na⁺ permeability, $\text{L}{}_{\mathrm{<mtext>Na</mtext>}}\text{= (}\text{?J}{}_{\mathrm{<mtext>Na</mtext>}}{}^{\mathrm{+}}\text{?Δ}\text{pNa}\text{)}{}_{\mathrm{<mtext>\Delta \psi ,\Delta </mtext><mtext>pH</mtext>}}$, it was 1620–2500 nmol Na⁺·(mg protein)^?1·h^?1·(pNa unit)^?1; and for the proton ‘cross-permeability’, $\text{L}{}_{\mathrm{<mtext>HNa</mtext>}}\text{= (}\text{?J}{}_{\mathrm{<mtext>H</mtext>}}{}^{\mathrm{+}}\text{?Δ}\text{pNa}\text{)}{}_{\mathrm{<mtext>\Delta \psi ,\Delta </mtext><mtext>pH</mtext>}}$, it was 220–580 nmol H⁺·(mg protein)^?1·h^?1·(pNa unit)^?1, for different preparations. From the above phenomenological parameters, the following quantities have been calculated: the degree of coupling (q), the maximal efficiency of Na⁺-H⁺ exchange (η_max), the flow and force efficacies (?) of the above exchange, and the admissible range for the values of the molecular stoichiometry parameter (r). We found q ? 0.4; η_max ? 5%; 0.36 ? r ? 2; ?_JNa⁺ ? 1.3 · 10⁵μmol · (RT unit)^?1 at J_Na = 1 μmolNa⁺ · (mgprotein)^?1 · h^?1; and ?_ΔpNa ? 5 · 10⁴ ΔpNa · (mg protein) · h · (RT unit)^?1 at ΔpNa = 1 unit, for different preparations.     

Temperature dependence of active K+ transport in cation dimorphic sheep erythrocytes

Arrhenius diagrams of K⁺ pump fluxes measured between 15°C and 41°C were discontinuous in high K⁺ but not in low K⁺ sheep red cells. Exposure of low K⁺ cells to anti-L caused a bimodal temperature response of K⁺ pump flux with a transition temperature, $\text{T}\text{c}$, similar to that found in high K⁺ cells but with comparatively higher activation energies above $\text{T}\text{c}$.     

The effects of environmental factors on growth and the chemical and biochemical composition of marine diatoms. I. Light and temperature effects

Temperature and light interact to modify the chemical and biochemical composition of a nitrogen-limited marine diatom, Thalassiosira allenii Takano, grown at a constant dilution rate in continuous culture and under a light:dark cycle.The percent of the total ¹⁴C incorporated into protein, polysaccharide and lipid, the N/C ratio and the C/cell varied with temperature in a markedly non-linear manner. The N/cell was negatively correlated to temperature. The Chl $\text{a}\text{C}$ ratio was positively correlated with temperature under saturating light and non-saturating light for temperatures > 25 °C, but was constant under non-saturating light conditions for temperatures < 25 °C.Productivity index (PI) was negatively correlated to temperature under saturating light conditions, but did not vary under low light. In each case, the variation in PI with temperature was governed by the variation in Chl $\text{a}\text{C}$.The dark carbon loss rate was exponentially related to temperature and independent of light. Variation in the percent of the total ¹⁴C incorporated into protein and polysaccharide, the $\text{N}\text{C}$ ratio and C/cell was primarily due to the effects of N-limitation < 20 °C and primarily due to the effects of temperature > 20 °C. Variation in N/cell was primarily due to the effects of temperature over the entire range of temperature studied. Variation in Chl $\text{a}\text{C}$ was caused by the interaction of temperature and light effects.In most cases, temperature and nutrient effects interacted to govern how a particular parameter varied with temperature while light affected the range of values over which the parameter varied.The percent of the total ¹⁴C incorporated into protein exhibited a significant linear relationship with $\text{N}\text{C}$.The dark carbon loss rate, $\text{N}\text{C}$ ratio and Chl $\text{a}\text{C}$ ratio data were used to test the applicability of a model for the physiological adaptation of unicellular algae. The model, with parameters derived from a non-linear least-squares fit of the dark carbon loss rate data, adequately described the $\text{N}\text{C}$ ratio between 15 and 25 °C at 290 and 137 μE · m^?2 · s^?1, but failed to describe the data at 28 °C and at 48 μE · m^?2 · s^?1. The Chl $\text{a}\text{C}$ ratio was adequately described by the model under all light and temperature conditions.     

Cytochalasin B inhibition and temperature dependence of 3-O-methylglucose transport in fat cells

The transport of $\text{3-O-}\text{methylglucose}$ in white fat cells was measured under equilibrium exchange conditions at $\text{3-O-}\text{methylglucose}$ concentrations up to 50 mM with a previously described method (Vinten, J., Gliemann, J. and Østerlind, K. (1976) J. Biol. Chem. 251, 794–800). Under these conditions the main part of the transport was inhibitable by cytochalasin B. The inhibition was found to be of competitive type with an inhibition constant of about 2.5 · 10^?7 M, both in the absence and in the presence of insulin (1μM). The cytochalasin B-insensitive part of the $\text{3-O-}\text{methylglucose}$ permeability was about 2 · 10^?9 cm · s^?1, and was not affected by insulin. As calculated from the maximum transport capacity, the half saturation constant and the volume/ surface ratio, the maximum permeability of the fat cell membrane to $\text{3-O-}\text{methylglucose}$ at 37°C and in the presence of insulin was 4.3 · 10^?6 cm · s^?1. From the temperature dependence of the maximum transport capacity in the interval 18–37°C and in the presence of insulin, an Arrhenius activation energy of $\text{14.8 ± 0.44}\text{kcal/mol}$ was found. The corresponding value was $\text{13.9 ± 0.89}$ in the absence of insulin. The half saturating concentration of $\text{3-O-}\text{methylglucose}$ was about 6 mM in the temperature interval used, and it was not affected by insulin, although this hormone increased the maximum transport capacity about ten-fold to 1.7 mmol · s^?1 per 1 intracellular water at 37°C.     

A simple procedure for resolution of Escherichia coli RNA polymerase holoenzyme from core polymerase.

The association constant, K_A, for myosin subfragment-1 binding to actin was measured as a function of ionic strength [KCl, LiCl, and tetramethylammonium chloride (TMAC)]and temperature by the method of time-resolved fluorescence depolarization. The following thermodynamic values were obtained from solutions of 0.20 × 10^?6m S-1, 1.00 × 10^?6m actin in 0.15 m KCl, pH 7.0, at 25 °C: ΔG ° = ?39 ± 1 kJ M^?1, ΔH⁰ = 44 ± 2 kJ M^?1 and $\text{ΔS}{}^0\text{= 0.28 ± 0.01 kJ}\text{M}{}^{\mathrm{?1}}{}^0\text{K}{}^{\mathrm{?1}}$. For measurements in KCl (0.05 to 0.60 m), In $\text{K}{}_{\mathrm{a}}\text{= ?8.36 (KCl)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Thus, the binding is endothermic and strongly inhibited by high ionic strength. When KCl was replaced by LiCl or TMAC the ionic effects on the binding were cation specific. The nature of actin-(S-1) binding in the rigor state is discussed in terms of these results.     

Kinetic parameters for the binding of p-nitrophenyl alpha-d-mannopyranoside to concanavalin A.

Binding of the chromogenic ligand p-nitrophenyl α-d-mannopyranoside to concanavalin A was studied in a stopped-flow spectrometer. Formation of the protein-ligand complex could be represented as a simple one-step process. No kinetic evidence could be obtained for a ligand-induced change in the conformation of concanavalin A, although the existence of such a conformational change was not excluded. The entire change in absorbance produced on ligand binding occurred in the monophasic process monitored in the stopped-flow spectrometer. The value of the apparent second-order rate constant (k_a) for complex formation (k_a = 54,000 s^?1m^? at 25 °C, pH 5.0, Γ/2 0.5) was independent of the protein concentration when the protein was in the range of 233–831 μm in combining sites and in excess of the ligand. The apparent first-order rate constant (k_?a) for dissociation of the complex was obtained from the rate constant for the decomposition of the complex upon the addition of excess methyl α-d-mannopyranoside (k_?a = 6.2 s^?1 at 25 °C, pH 5.0, Γ/2 0.5). The ratio $\text{k}{}_{\mathrm{<mtext>a</mtext>}}{}_{\mathrm{<mtext>?</mtext><mtext>a</mtext>}}$ (0.9 × 10₄m^?1) was in reasonable agreement with value of 1.1 ± 0.1 × 10⁴m^?1 determined for the equilibrium constant for complex formation by ultraviolet difference spectrometry. Plots of ln($\text{k}{}_{\mathrm{<mtext>a</mtext>}}\text{T}$) and ln($\text{k}{}_{\mathrm{<mtext>a</mtext>}}\text{T}$) vs $\text{1}\text{T}$ were linear (T is temperature) and were used to evaluate activation parameters. The enthalpies of activation for formation and dissociation of the complex are 9.5 ± 0.3 and 16.8 ± 0.2 kcal/mol, respectively. The unitary entropies of activation for formation and dissociation of the complex are 2.8 ± 1.1 and 1.3 ± 0.7 entropy units, respectively. These entropy changes are much less than those usually associated with substantial changes in the conformation of proteins.     

Pisum sativum and vicia faba carbohydrates: Part IV — Granular structure of wrinkled pea starch

The granular structure of wrinkled pea starch, compared to two other B-type starches, potato and amylomaize, has been studied, using physical, chemical and enzymic methods both before and after lintnerisation (2·2n HCl, 35°C). Wrinkled pea starch, which was composed mainly (90%) of compound granules, had an apparent amylose content of 75·4% when measured at +2°C. Native granules showed weak B-type crystallinity. The fraction (27·4%) which was easily degraded during lintnerisation and which corresponded to the amorphous phase, was smaller than for other starches. The degradation rate of the more organised phase was low (6% in 17 days). The residue remaining after exposure to acid for 42 days presented a very high, B-type crystallinity but with the same sorption properties as native starch, which indicates that water is part of the crystallites. The crystalline phase is composed of linear chains of $\text{DP}$ 25, distributed asymmetrically. The native starch showed a single gelatinisation endotherm between 117 and 133°C and with a ΔH of 0·7 cal. g^?1 dry starch, which is somewhat lower than other B-type starches.     

Respiration,energy balance and development during growth and starvation of Carcinus maenas L. larvae (Decapoda:Portunidae)

In all larval stages of Carcinus maenas L. oxygen consumption was measured at three temperatures (12,18,25 °C). Values increased during development and were in the range of 0.037 ± 0.01 (zoea-1, 12°C, $\text{x}\text{?}\text{± 95\% CL}$) to 0.734 ± 0.047 μl O₂ · h^?1 · ind^?1 (megalopa, 25 °C). Growing larvae showed temperature dependent trends in weight specific respiration rates (referred to dry wt; DW), with values between ≈2.4 and 9.4 μl O₂· h^?1·mg DW^?1. Increase in oxygen consumption of megalops did not differ much at temperatures between 18 and 25 °C. This points to an exceptional physiological position of this stage. Fed zoea-1 of C. maenas (18 °C) revealed growth rates in terms of 40% DW, 20% carbon (C), 30% nitrogen (N) and 65% hydrogen (H). At the same time larvae gained individual energy by 13% (J · ind^?1), while weight specific energy dropped by ≈ 19% (J · mg DW^?1) during the first day and remained constant until the moult. Starved zoea-1 of C. maenas (18 ° C) gained ≈ 20 % in DW through the first day, probably caused by inorganic salts which enter the organism after the moult of the prezoea. DW dropped to ≈ 25 % of initial value, when starvation continued. Single components decreased by ≈50% (C), 54% (N), 57% (J · ind^?1). Weight specific energy (J · mg DW^?1) decreased by 40% during the first 4 days of starvation, remaining constant thereafter. Individual respiration rate (R) dropped by 61 %, weight specific respiration rate (QO₂) by 55 %. Individual energy loss in starved zoea-1 was 0.077 J over a period of 11 days. In this period ≈ 9.3 μl O₂·ind^?1 were consumed. Thus effective oxygen capacity was lower than in growing larvae. It dropped to 5.3 J·mlO₂^?1 after 4 days and remained constant if starvation continued, i.e. 65 % of possible energy loss occurred during the first 4 days. Decrease in requirement for oxygen and its effective capacity were both recognized as independent components of survival during starvation. Partitioning of energy through individual larval development of C. maenas was investigated for all five larval stages. The cumulative budget could be calculated: consumption (C) = 28.23 J, growth (G) = 0.92 J, exoskeleton (Ex) = 0.20 J, metabolism (M) = 5.30 J, egestion and excretion (E) = 21.82 J. Mean gross and net growth efficiency were, K₁ = 3.3% and K₂ = 14.8%, respectively.     

Equilibrium constants under physiological conditions for the reactions of L-phosphoserine phosphatase and pyrophosphate: L-serine phosphotransferase

The observed equilibrium constants (K_obs) for the l-phosphoserine phosphatase reaction [EC 3.1.3.3] have been determined under physiological conditions of temperature (38 °C) and ionic strength (0.25 m) and physiological ranges of pH and free [Mg²⁺]. Using Σ and square brackets to indicate total concentrations $\text{K}{}_{\mathrm{<mtext>obs</mtext>}}\text{=}\text{Σ L-serine][Σ P}{}_{\mathrm{i}}\text{]}\text{Σ L-phosphoserine]H}{}_2\text{O]}\text{, K =}\text{L-H · serine}{}^{\mathrm{\pm }}\text{]HPO}{}_4{}^{\mathrm{2?}}\text{]}\text{[L-H · phosphoserine}{}^{\mathrm{2?}}\text{]H}{}_2\text{O]}$. The value of K_obs has been found to be relatively sensitive to pH. At 38 °C, K⁺] = 0.2 m and free [Mg²⁺] = 0; K_obs = 80.6 m at pH 6.5, 52.7 m at pH 7.0 [ΔG_obs⁰ = ?10.2 kJ/mol (?2.45 kcal/mol)], and 44.0 m at pH 8.0 ([H₂O] = 1). The effect of the free [Mg²⁺] on K_obs was relatively slight; at pH 7.0 ([K⁺] = 0.2 m) K_obs = 52.0 m at free [Mg²⁺] = 10^?3, m and 47.8 m at free [Mg²⁺] = 10^?2, m. K_obs was insignificantly affected by variations in ionic strength (0.12–1.0 m) or temperature (4–43 °C) at pH 7.0. The value of K at 38 °C and I = 0.25 m has been calculated to be 34.2 ± 0.5 m [ΔG_obs⁰ = ?9.12 kJ/mol (?2.18 kcal/ mol)]([H₂O] = 1). The K for the phosphoserine phosphatase reaction has been combined with the K for the reaction of inorganic pyrophosphatase [EC 3.6.1.1] previously estimated under the same physiological conditions to calculate a value of 2.04 × 10⁴, m [ΔG_obs⁰ = ?28.0 kJ/mol (?6.69 kcal/mol)] for the K of the pyrophosphate:l-serine phosphotransferase [EC 2.7.1.80] reaction. $\text{K}{}_{\mathrm{<mtext>obs</mtext>}}\text{=}\text{[}\text{Σ L-serine}\text{][}\text{Σ}\text{P}{}_{\mathrm{<mtext>i</mtext>}}\text{]}\text{[}\text{Σ L-phosphoserine}\text{][}\text{H}{}_2\text{O}\text{]}\text{, K =}\text{[L-H · serine}{}^{\mathrm{\pm }}\text{]HPO}{}_4{}^{\mathrm{2?}}\text{]}\text{[L-H · phosphoserine}{}^{\mathrm{2?}}\text{]H}{}_2\text{O}$. Values of K_obs for this reaction at 38 °C, pH 7.0, and I = 0.25 m are very sensitive to the free [Mg²⁺], being calculated to be 668 [ΔG_obs⁰ = ?16.8 kJ/mol (?4.02 kcal/mol)] at free [Mg²⁺] = 0; 111 [ΔG_obs⁰ = ?12.2 kJ/mol (?2.91 kcal/mol)] at free [Mg²⁺] = 10^?3, m; and 9.1 [ΔG_obs⁰ = ?5.7 kJ/mol (?1.4 kcal/mol) at free [Mg²⁺] = 10^?2, m). K_obs for this reaction is also sensitive to pH. At pH 8.0 the corresponding values of K_obs are 4000 [ΔG_obs⁰ = ?21.4 kJ/mol (?5.12 kcal/mol)] at free [Mg²⁺] = 0; and 97.4 [ΔG_obs⁰ = ?11.8 kJ/ mol (?2.83 kcal/mol)] at free [Mg²⁺] = 10^?3, m. Combining K_obs for the l-phosphoserine phosphatase reaction with K_obs for the reactions of d-3-phosphoglycerate dehydrogenase [EC 1.1.1.95] and l-phosphoserine aminotransferase [EC 2.6.1.52] previously determined under the same physiological conditions has allowed the calculation of K_obs for the overall biosynthesis of l-serine from d-3-phosphoglycerate. $\text{K}{}_{\mathrm{<mtext>obs</mtext>}}\text{=}\text{[}\text{Σ L-serine}\text{][}\text{Σ NADH}\text{][}\text{Σ}\text{P}{}_{\mathrm{<mtext>i</mtext>}}\text{][}\text{Σ}\text{α-}\text{ketoglutarate}\text{]}\text{[Σ d-3-}\text{phosphoglycerate}\text{][Σ NAD}{}^{\mathrm{+}}\text{][Σ L-glutamat0]}$ The value of K_obs for these combined reactions at 38 °C, pH 7.0, and I = 0.25 m (K⁺ as the monovalent cation) is 1.34 × 10^?2, m at free [Mg²⁺] = 0 and 1.27 × 10^?2, m at free [Mg²⁺] = 10^?3, m.     

Chemical composition and alkaline phosphatase activity of nutrient-saturated and P-deficient cells of four marine dinoflagellates

Four marine dinoflagellates, Amphidinium carterae Hulburt, Ceratium tripos (O.F. Müll.) Nitzsch, Prorocentrum minimum (Pav.) J. Schiller, and Scrippsiella trochoidea (Stein) Loeblich III were grown as dilution cultures at 18°C, S = 29%. and 30 μE·m^?2·s^?1 at L:D = 14:10 h. In nutrient-saturated cultures, the growth rates (doubl·day^?1) ranged from 0.38 for Scrippsiella to 0.80 for Prorocentrum, and carbon content (pg·cell^?1) from 83 for Amphidinium to 6900 for Ceratium. The atomic $\text{N}\text{C}$ ratio was 0.13–0.15, but for Ceratium it was 0.088, because of its thick, cellulose theca. The atomic $\text{N}\text{P}$ ratio ranged from 12–13 for Ceratium and Scrippsiella to 15–17 for Prorocentrum and Amphidinium. Under P-deficient conditions (growth rate 39–70% of the maximum), cellular P decreased considerably, but so did N, so that the $\text{N}\text{P}$ ratio was only slightly affected. There was a concomitant increase in carbon content per cell of 1.2- to 1.7-fold. Alkaline phosphatase activity was virtually nil in nutrient-saturated cells, but was readily demonstrable in all species when P-deficient.     

Interfacial adsorption of an inhalation anesthetic onto ionic surfactant micelles and its desorption by high pressure

The effects of pressure and temperature on the critical micelle concentration (CMC) of sodium dodecylsulfate (SDS) were measured in the presence of various concentrations of an inhalation anesthetic, methoxyflurane. The change in the partial molal volume of SDS on micellization, $\text{Δ}\text{V}{}_{\mathrm{<mtext>m</mtext>}}$, increased with the increase in the concentration of methoxyflurane. The CMC-decreasing power, which is defined as the slope of the linear plot between ln(CMC) vs. mole fraction of anesthetic, was determined as a function of pressure and temperature. Since the CMC-decreasing power is correlated to the micelle/water partition coefficient of anesthetic, the volume change of the transfer (ΔV_p^o) of methoxyflurane from water to the micelle can be determined from the pressure dependence of the CMC-decreasing power. The value of ΔV_p^o amounts 6.5±1.8 cm³·mol^?1, which is in reasonable agreement with the volume change determined directly from the density data, 5.5±0.6 cm³ · mol^?1. Under the convention of thermodynamics, this indicates that the application of pressure squeezes out anesthetic molecules from the micelle. The transfer enthalpy of anesthetic from water to the micelle is slightly endothermic. The partial molal volume of methoxyflurane in the micelle (112.0 cm³·mol^?1) is smaller than that in decane (120.5 cm³·mol^?1) and is larger than that in water (108.0 cm³·mol^?1). This indicates that the anesthetic molecules are incorporated into the micellar surface region, i.e., the palisade layer of the micelle in contact with water molecules, rather than into the micelle core.