Solution-phase disproportionation equilibria for monosubstituted Pentakis- (arylisocyanide)cobalt(I) complexes by proton-NMR studies

Equilibrium constants, K_dis, for the solvent- dependent, solution-phase disproportionation equilibria of monosubstituted pentakis(arlisocyanide)cobalt(I) complexes: 2[Co(CNR)₄L]⁺?[Co(CNR)₃L₂]⁺ + [Co(CNR)₅]⁺, K_dis = $\text{[Co(CNR)}{}_3\text{L}{}_2\text{][Co(CNR)}{}_5\text{]}\text{[Co(CNR)}{}_4\text{L]}{}^2$ are measured by planimeter-integration of proton- NMR spectra at ambient temperature. The complexes, [Co(CNR)₄L]ClO₄, R = 2,6-Me₂C₆H₃, L = P(C₆H₅)₃, P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = o-MeC₆H₄, L = P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = 2,4,6-Me₃C₆H₂, L = P(C₆H₅)₃; R = 2,6-Et₂C₆H₃, L = P(C₆H₅)₃; are investigated in the deuterated solvents, CDCl₃, CD₃CN, (CD₃)₂CO, C₅D₅N, CD₃NO₂, and (CD₃)₂SO. Disproportionation seems to occur in all [Co(CNR)₄L]⁺, but NMR study is facilitated by utilizing equivalent alkyl protons (i.e., Me-groups) on the RNC ligands.Correlation of K_dis values with steric-hindrance of the RNC in sets of complexes with the same P-ligand is evident in all solvents: K_dis decreases with increased steric-hindrance in RNC. The K_dis values for complexes with the same RNC and analogous triarylphosphine, triarylphosphite ligands (i.e., PR₃, P(OR)₃, same R) are approximately equal. The K_dis values for complexes of P-ligands with Cl-substituent are significantly larger than K_dis values for complexes with the corresponding unsubstituted P-ligands (e.g., [Co(CNR)₄P(C₆H₄Clp)₃]ClO₄vs. [Co(CNR)₄P(C₆H₅)₃]ClO₄) in (CD₃)₂CO and C₅D₅N solution, but are smaller in CDCl₃ and CD₃CN, and approximately equal in CD₃NO₂ and (CD₃)₂SO. Properties of the solvents are also considered.     

Kinetic studies on the reaction of ethylenediaminetetraacetatochromium(III) complex with hydrogen peroxide

The rate of reaction of [Cr(III)Y]_aq (Y is EDTA anion) with hydrogen peroxide was studied in aqueous nitrate media [μ = 0.10 M (KNO₃)] at various temperatures. The general rate equation, Rate = $\text{k}{}_1\text{+}\text{k}{}_2\text{K}{}_1\text{[H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{?1}}\text{1 +}\text{K}{}_1\text{[H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{?1}}$ [Cr(III)Y]_aq[H₂O₂] holds over the pH range 5–9. The decomposition reaction of H₂O₂ is believed to proceed via two pathways where both the aquo and hydroxo-quinquedentate EDTA complexes are acting as the catalyst centres. Substitution-controlled mechanisms are suggested and the values of the second-order rate constants k₁ and k₂ were found to be 1.75 × 10^?2 M^?1 s^?1 and 0.174 M^?1 s^?1 at 303 K respectively, where k₂ is the rate constant for the aquo species and k₂ is that for the hydroxo complex. The respective activation enthalpies (ΔH^*₁ = 58.9 and ΔH^*₂ = 66.5 KJ mol^?1) and activation entropies (ΔS^*₁ = ?85 and ΔS^*₂ = ?40 J mol^?1 deg^?1) were calculated from a least-squares fit to the Eyring plot. The ionisation constant pK₁, was inferred from the kinetic data at 303 K to be 7.22. Beyond pH 9, the reaction is markedly retarded and ceases completely at pH ? 11. This inhibition was attributed in part to the continuous loss of the catalyst as a result of the simultaneous oxidation of Cr(III) to Cr(VI).     

Adenosine triphosphate sulfurylase from Penicillium chrysogenum equilibrium binding, substrate hydrolysis, and isotope exchange studies.

ATP sulfurylase from Penicillium chrysogenum was purified to homogeneity. The enzyme binds 8 mol of free ATP (K_s = 0.53 mM) or AMP (K_s = 0.50 mM) per 440,000 g. The results are consistent with our earlier report that the enzyme is composed of eight identical subunits of M_r 55,000 (J. W. Tweedie and I. H. Segel, 1971, Prep. Biochem. 1, 91–117; J. Biol. Chem. 246, 2438–2446). In the absence of cosubstrates, the purified enzyme catalyzes the hydrolysis of MgATP (to AMP and MgPP_i) and adenosine 5′-phosphosulfate (APS) (to AMP and SO₄^2?). MgATP hydrolysis is inhibited by nonreactive sulfate analogs such as nitrate, chlorate, and formate (uncompetitive with MgATP). In spite of the hydrolytic reactions it is possible to observe the binding of MgATP and APS to the enzyme in a qualitative (nonequilibrium) manner. Neither inorganic sulfate (the cosubstrate of the forward reaction) nor formate or inorganic phosphate (inhibitors competitive with sulfate) will bind to the free enzyme in detectable amounts in the absence or in the presence of Mg²⁺, Ca²⁺, free ATP, or a nonreactive analog of MgATP such as Mg-α,β-methylene-ATP. Similarly, inorganic pyrophosphate (the cosubstrate of the reverse reaction) will not bind in the absence or in the presence of Mg²⁺ or Ca²⁺. The induced binding of ³²P_i (presumably to the sulfate site) can be observed in the presence of MgATP. The results are consistent with the obligately ordered binding sequence deduced from the steady-state kinetics (J. Farley et al., 1976, J. Biol. Chem. 251, 4389–4397) and suggest that the subsites for SO^2?₄ or MgPP_i appear only after nucleotide cleavage to form E~AMP · MgPP_i or E~AMP · SO₄ complexes. The suggestion is supported by the relative values of K_ia (ca. 1 mm for MgATP) and K_iq (ca. 1 αm for APS) and by the inconsistent value of k_?1 calculated from $\text{V}{}_{\mathrm{<mtext>f</mtext>}}\text{K}{}_{\mathrm{<mtext>i</mtext><mtext>a</mtext>}}\text{K}{}_{\mathrm{<mtext>m</mtext><mtext>A</mtext>}}$ (The value is considerably less than V_r) Purified ATP sulfurylase will also catalyze a Mg³²PP_i-MgATP exchange in the absence of SO₄^2?. A ³⁵SO₄^2?-APS exchange could not be demonstrated in the absence or presence of MgPP_i. This result was not unexpected: The rate of APS hydrolysis (or conversion to MgATP) is extremely rapid compared to the expected exchange rate. Also, the pool of APS at equilibrium is extremely small compared to the sulfate pool. The V values for molybdolysis, APS hydrolysis (in the absence of PP_i), ATP synthesis (from APS + MgPP_i), and Mg³²PP_i-MgATP exchange at saturating sulfate are all about equal (12–19 μmol × min^?1 × mg of enzyme^?1). The rates of Mg³²PP_i-MgATP exchange in the absence of sulfate, APS synthesis (from MgATP + sulfate), and MgATP hydrolysis (in the absence of sulfate) are considerably slower (0.10 – 0.35 μmol × min^?1 × mg of enzyme^?1). These results and the fact that k₄ calculated from $\text{V}{}_{\mathrm{<mtext>r</mtext>}}\text{K}{}_{\mathrm{<mtext>i</mtext><mtext>q</mtext>}}\text{K}{}_{\mathrm{<mtext>m</mtext><mtext>Q</mtext>}}$ is considerably larger than V_f suggest that the rate-limiting step in the overall forward reaction is the isomerization reaction E~AMP-SO^2?₄ → EAPS. In the reverse direction the rate-limiting step may be SO^2?₄ release or isomerization of the E~AMP · MgPP_i · SO₄^2? complex. (The reaction appears to be rapid equilibrium ordered.) Reactions involving the synthesis or cleavage of APS are specific for Mg²⁺. Reactions involving the synthesis or cleavage of ATP will proceed with Mg²⁺, with Mn²⁺, and, at a lower rate, with Co²⁺. The results suggest that the enzyme possesses a Mg²⁺-preferring divalent cation (activator) binding site that is involved in APS synthesis and cleavage and is distinct from the MeATP or MePP_i site. The equilibrium binding of about one atom of ⁴⁵Ca²⁺ per subunit (possibly to the activator site) could be demonstrated (K_s = 1.4 mM).     

Studies of the nucleotide-binding sites on the mitochondrial F1-ATPase through the use of a photoactivable derivative of adenylyl imidodiphosphate

(1) $\text{N-4-}\text{Azido}\text{-2-}\text{nitrophenyl}\text{-γ-[}{}^3\text{H]aminobutyryl-Ado}\text{PP[}\text{NH}\text{]P(}\text{NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P)}$ a photoactivable derivative of 5-adenylyl imidodiphosphate (AdoPP[NH]P), was synthesized. (2) Binding of ³H]NAP₄-AdoPP[NH]P to soluble ATPase from beef heart mitochrondria (F₁) was studied in the absence of photoirradiation, and compared to that of $\text{[}{}^3\text{H]Ado}\text{PP[}\text{NH}\text{]P}$. The photoactivable derivative of AdoPP[NH]P was found to bind to F₁ with high affinity, like AdoPP[NH]P. Once $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}$ had bound to F₁ in the dark, it could be released by AdoPP[NH]P, ADP and ATP, but not at all by NAP₄ or AMP. Furthermore, preincubation of F₁ with unlabeled AdoPP[NH]P, ADP, or ATP prevented the covalent labeling of the enzyme by $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}$ upon photoirradiation. (3) Photoirradiation of F₁ by $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}$ resulted in covalent photolabeling and concomitant inactivation of the enzyme. Full inactivation corresponded to the binding of about 2 mol $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}\text{mol F}{}_1$. Photolabeling by NAP₄-AdoPP[NH]P was much more efficient in the presence than in the absence of MgCl₂. (4) Bound $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}$ was localized on the α- and β-subunits of F₁. At low concentrations (less than 10 μM), bound $\text{[}{}^3\text{H]NAP}{}_4\text{-}\text{Ado}\text{PP[}\text{NH}\text{]P}$ was predominantly localized on the α-subunit; at concentrations equal to, or greater than 75 μM, both α- and β-subunits were equally labeled. (5) The extent of inactivation was independent of the nature of the photolabeled subunit (α or β), suggesting that each of the two subunits, α and β, is required for the activity of F₁. (6) The covalently photolabeled F₁ was able to form a complex with aurovertin, as does native F₁. The ADP-induced fluorescence enhancement was more severely inhibited than the fluorescence quenching caused by ATP. The percentage of inactivation of F₁ was virtually the same as the percentage of inhibition of the ATP-induced fluorescence quenching, suggesting that fluorescence quenching is related to the binding of ATP to the catalytic site of F₁.     

Ruthenium(II) complexes derived from 2-(methylamino)pyridine

2-(Methylamino)pyridine reacts with RuCl₂(CO)₃ to give a carbamoyl complex, [$\text{Ru(C(O)N(CH}{}_3\text{)(C}{}_5\text{H}{}_4\text{N}$)Cl(CO)₂], which yields with pyridine (py) and acetylacetone (Hacac), respectively, [$\text{Ru(C(O)N(CH}{}_3\text{)C}{}_5\text{H}{}_4\text{N}$)Cl(CO)₂(py)] and [$\text{Ru(C(O)N(CH}{}_3\text{)C}{}_5\text{H}{}_4\text{N}$)(CO)₂(acac)]. These complexes are characterized spectroscopically. The amino group of the ligand is carbonylated and the resulted carbamoyl ligand is chelating through a pyridine ring-N and a carbamoyl-C atom. 2-Aminopyridine and 2-aminopyrimidine react similarly with RuCl₂(CO)₃ to give the corresponding carbamoyl complexes.     

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.     

The covariance of relatives derived from a random mating population.

Attention is drawn to errors common in the derivation of forms for the genotypic covariance of noninbred relatives from a Hardy-Weinberg population of diploids. A synthesis of Fisher's least-squares method of partitioning the genotypic variance and Malécot's probability method of expressing kinship, yields a general form. For one locus, the form is $\text{(P}{}_{\mathrm{ss}}\text{+ P}{}_{\mathrm{sd}}\text{+ P}{}_{\mathrm{ds}}\text{+ P}{}_{\mathrm{dd}}\text{)}\text{1}\text{2}\text{σ}{}_{\mathrm{a}}{}^2\text{+ (P}{}_{\mathrm{ss}}\text{P}{}_{\mathrm{dd}}\text{+ P}{}_{\mathrm{sd}}\text{P}{}_{\mathrm{ds}}\text{) σa}{}_{\mathrm{d}}{}^2$, where σ_a² is the additive genetic variance, α_d² is the variance of dominance deviations, p_ij is the probability that parental gamete i is identical by descent to parental gamete j, i = s, d indexes the parents of one relative, and j = s, d indexes those of the other. The form provides a framework for obtaining the covariance of relatives from an equilibrium population with linkage.     

Dipole moments of random coil polypeptides

The Rotational Isomeric States model is applied to calculate dipole moments of polypeptides of the twenty natural α-amino acids in the random coil state. Dipole moments of each repeat unit (μ_i), are evaluated using a quantum mechanics procedure. Dipole moment ratios ($\text{D}{}_{\mathrm{x}}\text{=}\text{〈μ}{}^2\text{〉}\text{x}\text{μ}{}_{\mathrm{i}}{}^2\text{,}\text{x = number of repeat units}$) of homopolypeptides are calculated and extrapolated to x →?. With a few exceptions, D_? = 0.36 ± 0.1. Ten actual proteins and three enzymes are also studied; their dipole ratios (D_x′ =〈μ〉/x) range from 7.34 to 10.57 in 10^?59 C² m² (6.6–9.5 D²). Diffferences in the values of D_x′ are due mainly to the different contributions, μ_i, of the amino acid residues contained in each polymer, whereas the sequence of amino acids has a very minor effect.     

Respiration-driven proton translocation with nitrite and nitrous oxide in Paracoccus denitrificans

(1) $\text{H}$⁺/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O₂, NO^?₂ or N₂O. Under optimal H⁺-translocation conditions, the ratios $\text{H}{}^{\mathrm{+}}\text{O}$, $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO^?₂ or N₂O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were ?0.84, ?2.33 and ?1.90, respectively. (3) The $\text{H}{}^{\mathrm{+}}\text{oxidant}$ ratios, mentioned in item 2, were not altered in the presence of $\text{valinomycin}\text{K}{}^{\mathrm{+}}$ and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O₂, NO^?₂ and N₂O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO^?₂, N₂O or O₂ pass two H⁺-translocating sites. The $\text{H}{}^{\mathrm{+}}\text{electron}$ acceptor ratios predicted by this scheme are in good agreement with the experimental values.     

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.     

Effect of N-alkyl-N,N,N-trimethylammonium ions on phosphatidylcholine model membrane structure as studied by 31P-NMR

The interaction of |C_nH_2n+1N⁺(CH₃)₃| · I^? (n = 3, 6, 9, 12, 14, 16 or 18) with egg-yolk phosphatidylcholine-water dispersions has been studied by ³¹P-NMR spectroscopy. It is shown that the effective anisotropy of ³¹P chemical shift (?Δσ_eff) of the lamellar phospholipid liquid-crystalline phase L_α increases with increasing concentration and alkyl chain length of the drug. Addition of $\text{|}\text{C}{}_6\text{H}{}_{13}\text{N}{}^{\mathrm{+}}\text{(CH}{}_3\text{)}{}_3\text{| ·I}{}^{\mathrm{?}}$ or |C₉H₁₉N⁺(CH₃)₃|·I^? to the phospholipid-water dispersion at a molar ratio ammonium salt:phospholipid > 0.8 induces in the dispersion a structure with an effective isotropic phospholipid motion. This structure is unstable and slowly transforms into the hexagonal phase. These effects have not been observed in phospholipid-water dispersions mixed with the ammonium derivatives with the longer alkyl chains n  12, 14, 16 or 18. It is proposed that these results might explain the effects of the investigated drugs on the nerve, muscle and bacterial cells.     

Flow analysis in a biological system adopting the buffer capacitor concept.

The flow measurement of each component in each compartment is important in works on transport phenomena in a biological system. The method of flow measurement was studied adopting the capacitor concept derived from network thermodynamics.A biologically active component i in a compartment is defined as follows,

$\text{n}{}_{\mathrm{i}}\text{=n}{}_1\text{+n}{}_2\text{=c}{}_1\text{V+c}{}_2\text{V}$

where the total quantity ni consists of a measurable form n_i (free form, conc. c₁) and concealed form n₂ (conc, c₂). Capacitor for the species i of a compartment is defined as follows,

$\text{C=}\text{d}\text{n}{}_{\mathrm{i}}\text{d}\text{μ}{}_{\mathrm{i}}\text{=}\text{1+}\text{c}{}_2\text{c}{}_1\text{c}{}_1\text{dV}\text{dμ}{}_{\mathrm{i}}\text{+}\text{1+}\text{dc}{}_2\text{dc}{}_1\text{v}\text{dc}{}_1\text{dμ}{}_{\mathrm{i}}$

,

$\text{=Ac}{}_1\text{dV}\text{dμ}{}_{\mathrm{i}}\text{+BV}\text{d}\text{c}{}_1\text{d}\text{t}$

Thus flow of each component is expressed as,

$\text{J}{}_{\mathrm{i}}\text{=}\text{d}\text{n}{}_{\mathrm{i}}\text{d}{}_{\mathrm{i}}\text{=}\text{d}\text{n}{}_{\mathrm{i}}\text{dμ}{}_{\mathrm{i}}\text{dμ}\text{n}{}_{\mathrm{i}}\text{dt}\text{=C}\text{d}\text{μ}{}_{\mathrm{i}}\text{dt}$

,

$\text{=Ac}{}_1\text{d}\text{V}\text{dt}\text{+BV}\text{d}\text{c}{}_1\text{dt}$

Method of determination of capacitor coefficients A and B by titration experiment was also considered. For an experimental case, the capacitance for H⁺ of blood compartment was determined. The relationship between the capacitor concept and the buffer value of Van Slyke was discussed.     

Photosystem II energy coupling in chloroplasts with H2O2 as electron donor

NH₂OH-treated, non-water-splitting chloroplasts can oxidize H₂O₂ to O₂ through Photosystem II at substantial rates (100–250 μequiv · h^?1 · mg^?1 chlorophyll with 5 mM H₂O₂) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H₂O₂ → Photosystem II → dimethylquinone reaction supports phosphorylation with a $\text{P}\text{e}{}_2$ ratio of 0.25–0.35 and proton uptake with $\text{H}{}^{\mathrm{+}}\text{e}$ values of 0.67 (pH 8)–0.85 (pH 6). These are close to the $\text{P}\text{e}{}_2$ value of 0.3–0.38 and the $\text{H}{}^{\mathrm{+}}\text{e}$ values of 0.7–0.93 found in parallel experiments for the H₂O → Photosystem II → dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor → Photosystem II → dibromothymoquinone (→O₂) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I^?, ferrocyanide).     

Effects of 5-hydroxylysine on acetylene reduction and NH4+-assimilation in the cyanobacterium Anabaena cylindrica.

5-hydroxylysine, an analogue of glutamate and lysine, causes $\text{NH}{}_4{}^{\mathrm{+}}$ production by N₂-fixing A. cylindrica; it also reversibly inhibits GS activity in vitro but has no effect on alanine dehydrogenase or GOGAT. On adding 5-hydroxylysine intracellular pools of glutamine, glutamate and aspartate decrease; those of alanine and serine increase. 5-hydroxylysine alleviates the inhibitory effect of $\text{NH}{}_4{}^{\mathrm{+}}$ on heterocyst production and C₂H₂ reduction and in $\text{NH}{}_4{}^{\mathrm{+}}\text{-grown}$ cultures results in heterocyst synthesis and in C₂H₂ reduction. The data suggest that the GS-GOGAT pathway is the sole route of importance in primary $\text{NH}{}_4{}^{\mathrm{+}}$ assimilation in A. cylindrica, that $\text{NH}{}_4{}^{\mathrm{+}}$ alone does not inhibit nitrogenase and heterocyst production, and that GS and/or a product is involved in regulating the production of both.     

On equivalent forms of Whittaker's similarity index

For two N-species assemblages A, B with specific proportionate abundances of the ith species a_i, b_l respectively, we consider the equality

$\text{∑}\text{t=1}\text{N}\text{c}{}_{\mathrm{i}}\text{= 1?}\text{1}\text{2}\text{∑}\text{t=1}\text{N}\text{|a}{}_{\mathrm{i}}\text{?b}{}_{\mathrm{i}}\text{|, c}{}_{\mathrm{i}}\text{=}\text{a}{}_{\mathrm{i}}\text{a}{}_{\mathrm{i}}\text{? b}{}_{\mathrm{i}}\text{b}{}_{\mathrm{i}}\text{a}{}_{\mathrm{i}}\text{> b}{}_{\mathrm{i}}\text{, 0?a,b,c?1}$

. The left-hand term is known as Sanders' minimum faunal abundance value, while the right side is referred to as Whittaker's similarity index. Both measures are commonly used in community studies. Equality between these two measures obtains only when proportionate abundances are utilized. We develop equivalent formulation which is valid for absolute abundance data, reduces to the Sanders-Whittaker equality when proportionate abundance data are employed, and is more sensitive to differences in species abundance distributions. Namely, we show that

$\text{2}\text{α+β}\text{∑}\text{t=1}\text{N}\text{c}{}_{\mathrm{i}}\text{= 1 ?}\text{1}\text{α+β}\text{∑}\text{t=1}\text{N}\text{|a}{}_{\mathrm{i}}\text{?b}{}_{\mathrm{i}}\text{|}$

, where

$\text{α =}\text{∑}\text{t=1}\text{N}\text{a}{}_{\mathrm{i}}\text{, β =}\text{∑}\text{t=1}\text{N}\text{b}{}_{\mathrm{i}}$

, and the a's, b's c's are as defined above.     

Inhibition of chymotrypsin by alkyl phosphonates: a quantitative structure-activity analysis.

A quantitative structure-activity relationship has been formulated for 53 alkyl phosphonates [R₂OPO(CH₃)SR₃] inhibiting chymotrypsin: . In this so-called bilinear model, k_i is the bimolecular rate constant (m^?1 s^?1), β is a disposable parameter evaluated by a computerized iterative procedure, MR is the molar refractivity of a substituent, $\text{σ}{}_3{}^1$ is Taft's polar parameter, and I is an indicator variable for substituents containing a sulfonium group. The correlation coefficient for this equation is 0.985. This quantitative structure-activity relationship is compared with those previously formulated for the action of chymotrypsin on acylamino acid ester substrates.     

Evidence for general catalysis and formation of nitrobenzene in the oxidation of phenylhydroxylamine in aqueous phosphate buffer

N-Phenylhydroxylamine is oxidized in aqueous phosphate buffer to nitrosobenzene, nitrobenzene, and azoxybenzene. Degradation is O₂ dependent and shows general catalysis by $\text{H}{}_2\text{PO}{}_4{}^{\mathrm{?}}$ (k₁ = 2.3 M^?2 sec^?1) and $\text{PO}{}_4{}^{\mathrm{?3}}$ (k₂ = 2.3 × 10⁵M^?2 sec^?1) or kinetically equivalent terms. Evidence is presented suggesting the intermediacy of a highly reactive species leading to these products.     

A Cl−/HCO3−-ATPase in the gils of Carassius Auratus. Its inhibition by thiocyanate

An ATPase is demonstrated in plasma membrane fractions of goldfish gills. This enzyme is stimulated by Cl^? and HCO₃^?, inhibited by SCN^?.Biochemical characterization shows that HCO₃^? stimulation ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{= 2.5}\text{mequiv./l}$) is specifically inhibited in a competitive fashion by SCN^? ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.25}\text{mequiv./l}$). The residual Mg²⁺-dependent activity is weakly is weakly affected by SCN^?.In the microsomal fraction chloride stimulation of the enzyme occurs in the presence of HCO₃^? ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{for chloride = 1 mequiv./l}$); no stimulation is observed in the absence of HCO₃^?. Thiocyanate exhibits a mixed type of inhibition ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.06}\text{mequiv./l}$) towards the Cl^? stimulation of the enzyme.Bicarbonate-dependent ATPase from the mitochondrial fraction is stimulated by Cl^?, but this enzyme has a relatively weak affinity for this substrate ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{= 14}\text{mequiv./l}$).