Anaerobic stimulation of sugar transport in avian erythrocytes

The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic and anaerobic conditions. In anaerobic cells, transport measurements with $\text{3-O-[}{}^{14}\text{C}\text{]}$ methylglucose resulted in a set of similar dissociation-like constants. Thus the Michaelis constants of $\text{3-O-[}{}^{14}\text{C}\text{]}$ methylglucose entry and exit, $\text{K}{}_{\mathrm{<mtext>so</mtext>}}$ and $\text{K}{}_{\mathrm{<mtext>si</mtext>}}$, were 8 and 7 mM, respectively. The equilibrium exchange constant, $\text{B}{}_{\mathrm{<mtext>s</mtext>}}$, and the counterflow constant, $\text{R}{}_{\mathrm{<mtext>s</mtext>}}$, were 9 and 11 mM, respectively. The activity constant for $\text{3-O-}\text{methylglucose}$ transport, $\text{F}{}_{\mathrm{<mtext>s</mtext>}}$, defined as $\text{V/K}{}_{\mathrm{<mtext>m</mtext>}}$, was 4 ml/h per g. This set of kinetic constants was compatible with a symmetrical mobile-carrier model. In contrast, the Michaelis constant for glucose entry, $\text{K}{}_{\mathrm{<mtext>go</mtext>}}$, was 2 mM and less than the counterflow constant, $\text{R}{}_{\mathrm{<mtext>g</mtext>}}$ (8 mM). This result could be accounted for by slower movement of the glucose-carrier complex than the free carrier. The activity constant for glucose transport, $\text{F}{}_{\mathrm{<mtext>g</mtext>}}$, was 5 ml/h perg.Under aerobic conditions, two of the dissociation-like constants ($\text{K}{}_{\mathrm{<mtext>si</mtext>}}$ and $\text{B}{}_{\mathrm{<mtext>s</mtext>}}$) for $\text{3-O-}\text{methylglucose}$ transport were significantly larger than those obtained in anaerobic cells, but the remaining two ($\text{K}{}_{\mathrm{<mtext>so</mtext>}}$ and $\text{R}{}_{\mathrm{<mtext>s</mtext>}}$) remained unchanged. The values, for $\text{K}{}_{\mathrm{<mtext>so</mtext>}}\text{, K}{}_{\mathrm{<mtext>si</mtext>}}\text{, B}{}_{\mathrm{<mtext>s</mtext><mtext>\; and</mtext>}}\text{R}{}_{\mathrm{<mtext>s</mtext>}}$ were 8, 26, 20 and 8 mM, respectively. The activity constant, $\text{F}{}_{\mathrm{<mtext>s</mtext>}}$, decreased to 2 ml/h per g. These changes in kinetic constants were consistent with the hypothesis that anoxia accelerated sugar transport by releasing free carrier that was previously sequestered on the inside of the cell membrane.     

Constraint on the substrate cytochrome P-450 binding reaction in bovine adrenocortical microsomes at physiological temperature

The addition of cholate to the microsomes at 37.5°C resulted in a striking decrease in the apparent substrate dissociation constant ($\text{K′}{}_{\mathrm{<mtext>s</mtext>}}$) and its temperature dependency. The microsomal membranes depleted of 80% of the lipids preserved the temperature dependency of the $\text{K}{}_{\mathrm{<mtext>s</mtext>}}$ and exhibited breaks in the Van't Hoff plot at the characteristic temperature of the lipids phase transition. The results indicate that the cytochrome $\text{P-450}$ is considerably restrained from expressing its maximum substrate binding potential at physiological temperature. In addition, the results indicate that the majority of the lipids apparently do not play a significant role in imposing constraint on the substratecytochrome $\text{P-450}$ binding reaction and in the temperature dependency of the $\text{K}{}_{\mathrm{<mtext>s</mtext>}}$.     

Mean solute concentration for use with the michaelis-menten equation applied to the analysis of data from intestinal perfusion experiments

A number of algebraic expressions for the solute concentration for use with the Michaelis-Menten equation during the analysis of data from intestinal perfusion experiments have been investigated. It is concluded that the most suitable, especially if water absorption is occuring, is of the form: $\text{s=(s}{}_{\mathrm{<mtext>initial</mtext>}}\text{? s}{}_{\mathrm{<mtext>efluent</mtext>}}\text{)/In(s}{}_{\mathrm{<mtext>initial</mtext>}}\text{/s}{}_{\mathrm{<mtext>effluent</mtext>}}\text{)}$.     

Thiophosphorylation of (Na + K+)-ATPase yields an ADP-sensitive phosphointermediate

(1) Treatment of $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ from rabbit kidney outer medulla with the $\text{γ-}{}^{35}\text{S}$ labeled thio-analogue of ATP in the presence of $\text{Na}{}^{\mathrm{+}}\text{+ Mg}{}^{\mathrm{2+}}$ and the absence of K⁺ leads to thiophosphorylation of the enzyme. The $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ value for [γ-S]ATP is 2.2 μM and for Na⁺ 4.2 mM at 22°C. Thiophosphorylation is a sigmoidal function of the Na⁺ concentration, yielding a Hill coefficient $\text{n}\text{H}\text{= 2.6}$. (2) The thio-analogue ($\text{K}{}_{\mathrm{<mtext>m</mtext><mtext>\; =\; 35\; \mu M</mtext>}}$) can also support overall $\text{(Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}\text{)-ATPase}$ activity, but $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ at 37°C is only $\text{1.3 γ}\text{mol}\text{· (mg protein)}{}^{\mathrm{?}}\text{·}$ h^?1 or 0.09% of the specific activity for ATP ($\text{K}{}_{\mathrm{<mtext>m</mtext><mtext>\; =\; 0.43\; mM</mtext>}}$). (3) The thiophosphoenzyme intermediate, like the natural phosphoenzyme, is sensitive to hydroxylamine, indicating that it also is an acylphosphate. However, the thiophosphoenzyme, unlike the phosphoenzyme, is acid labile at temperatures as low as 0°C. The acid-denatured thiophosphoenzyme has optimal stability at pH 5–6. (4) The thiophosphorylation capacity of the enzyme is equal to its phosphorylation capacity, indicating the same number of sites. Phosphorylation by ATP excludes thiophosphorylation, suggesting that the two substrates compete for the same phosphorylation site. (5) The (apparent) rate constants of thiophosphorylation (0.4 s^?1 vs. 180 s^?1), spontaneous dethiophosphorylation (0.04 s^?1 vs. 0.5 s^?1) and K⁺-stimulated dethiophosphorylation (0.54 s^?1 vs. 230 s^?1) are much lower than those for the corresponding reactions based on ATP. (6) In contrast to the phosphoenzyme, the thiophosphoenzyme is ADP-sensitive (with an apparent rate constant in ADP-induced dethiophosphorylation of 0.35 s^?1, $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$$\text{ADP = 48 μM at 0.1 mM ATP}$) and is relatively K⁺-insensitve. The $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ for K⁺ in dethiophosphorylation is 0.9 mM and in dephosphorylation 0.09 mM. The thiophosphoenzyme appears to be for 75–90% in the ADP-sensitive E₁-conformation.     

Binding of the structural protein soc to the head shell of bacteriophage T4

Qβ plus strands with a 70 S ribosome bound to the coat cistron initiation site were used as template for Qβ replicase. Minus strand synthesis proceeded until the replicase reached the ribosome. The ribosome was removed and elongation was continued in a substrate-controlled, stepwise fashion. The nucleotide analog N⁴-hydroxyCMP was introduced into the positions complementary to the third and fourth nucleotides of the coat cistron. The minus strands were elongated to completion, purified and used as template for Qβ replicase. The final plus strand preparation consisted of four species, with the sequences -A-U-G-G- (wild type), -A-U-A-G- (mutant C₃), -A-U-G-A- (mutant C₄) and -A-U-A-A- (mutant $\text{C}{}_3\text{C}{}_4$) at the coat initiation site. The ribosome binding capacity of the mutant RNAs relative to wild type was <0.1 (C₃), 3.2 (C₄) and 0.3 ($\text{C}{}_3\text{C}{}_4$). The finding that mutant C₃ no longer formed an initiation complex suggests that the interaction of the ribosome binding site with fMet-tRNA plays an essential role in the formation of the 70 S initiation complex. The fact that mutant C₄ RNA bound more efficiently than wild type, and that mutant $\text{C}{}_3\text{C}{}_4$ RNA showed substantial ribosome binding capacity whereas the single mutant C₃ did not, can be explained by assuming that an A residue following the A-U-G triplet interacts with a complementary U residue in the anticodon loop sequence. In the case of $\text{C}{}_3\text{C}{}_4$ this additional base-pair may offset the reduced codon-anticodon interaction resulting from the modification of the A-U-G codon.     

Kinetics of phospholipid exchange between bilayer membranes

In an accompanying publication by Duckwitz-Peterlein, Eilenberger and Overath ((1977) Biochim. Biophys. Acta 469, 311–325) it is shown that the exchange of lipid molecules between negatively charged vesicles consisting of total phospholipid extracts from Escherichia coli occurs by the transfer of single lipid monomers or small micelles through the water. Here a kinetic interpretation is presented in terms of a rate constant, $\text{k}{}_{\mathrm{?}}$, for the escape of lipid molecules from the vesicle bilayer into the water. The evaluated rate constants are $\text{k}{}_{\mathrm{?}}{}^{\mathrm{<mtext>P</mtext>}}\text{= (0.86 ± 0.05) · 10}{}^{\mathrm{?5}}\text{s}{}^{\mathrm{?1}}$ and $\text{k}{}_{\mathrm{?}}{}^{\mathrm{<mtext>E</mtext>}}\text{= (1.09 ± 0.13) · 10}{}^{\mathrm{?6}}\text{s}{}^{\mathrm{?1}}$ for phospholipid molecules with $\text{trans-}\text{Δ}{}^9\text{-hexadecenoate}$ and $\text{trans-}\text{Δ}{}^9\text{-octadecenoate}$, respectively, as the predominant acyl chain component. The rate constants are discussed in terms of the acyl chain and polar head group composition of the lipids.     

A chloride requirement for Na+-dependent amino-acid transport by brush border membrane vesicles isolated from the intestine of a mediterranean teleost (Boops salpa)

The uptake of d-glucose, 2-aminoisobutyric acid and glycine was studied with intestinal brush border membrane vesicles of a marine herbivorous fish: Boops salpa. The uptake of these three substances is stimulated by an Na⁺ electrochemical gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{C}{}_{\mathrm{<mtext>in</mtext>}}$). For glucose, an increase of the electrical membrane potential generated by a concentration gradient of the liposoluble anion, SCN^?, increases the Na⁺-dependent transport. This responsiveness to the membrane potential was confirmed by valinomycin. Differently from glucose, uptake of glycine and 2-aminoisobutyric acid requires, besides the Na⁺ gradient, the presence of Cl^? on the external side of the vesicles. In the absence of Cl^?, amino acid uptake is not stimulated by the Na⁺ gradient and is not influenced by an electrical membrane potential generated by SCN^? gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{>C}{}_{\mathrm{<mtext>in</mtext>}}$) or by a K⁺ diffusion potential ($\text{C}{}_{\mathrm{<mtext>in</mtext>}}\text{>C}{}_{\mathrm{<mtext>out</mtext>}}$). This Cl^? requirement differs from the Na⁺ requirement, since a Cl^? gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{>C}{}_{\mathrm{<mtext>in</mtext>}}$) does not result in an accumulation of glycine or 2-aminoisobutyric acid similar to that produced by an Na⁺ gradient.     

Transversal mobility in bilayer membrane vesicles: Use of pyrene lecithin as optical probe

Pyrene lecithin, a new excimer-forming lipid molecule, has been synthesized to examine the transversal mobility of probe molecules in lecithin bilayer vesicles. The rate of the lipid exchange is obtained by following the excimer yield as a function of time after mixing of fluorescence doped and undoped vesicles. A rapid exchange ($\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 11}\text{s}$) is followed by a slow transfer ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 8}\text{h}$). Above the lipid phase transition the fast transfer can be attributed to an exchange of lipid molecules from the outer layer of one vesicle to the outer layer of another one. The slow exchange is interpreted in terms of the ‘flip-flop’ process between the two layers of a single bilayer vesicle.Using pyrene and pyrene decanoic acid as probe molecules only the fast transfer through the water phase is observed ($\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 4}\text{s}$ for pyrene and $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 7}\text{s}$ for pyrene decanoic acid). This indicates that molecules like fatty acids or apolar membrane constituents must equilibrate very rapidly in a single bilayer vesicle.The water solubility or the critical micelle concentration of the probe molecules is determined and related to the transfer rates. An exchange process through the water phase via a monomeric state can be excluded.     

Comformation and absolute configuration of -methyllanthionine

If the bicyclic peptide ring proposed by Gross $\text{et}$$\text{al}$. (1,2) does in fact exist in nisin and related antibiotics, then the unusual β-methyllanthionine component must be significantly distorted from its conformation in the free state, as determined by x-ray structure analysis. The torsion angles about the SC_β bonds are 50–100° from the torsion angles in models of the sulfur-bridged peptide ring proposed for nisin. The chirality of the methylated β-carbon atom is (S). The conformation of the amino acid differs from that of $\text{meso}$-lanthionine only by a 180° rotation of a carboxyl group about the $\text{C}{}_{\mathrm{\alpha }}{}^{\mathrm{D}}\text{C}{}_{\mathrm{\beta }}\text{(CH}{}_3\text{)}$ bond.     

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.     

Dielectric dispersion of a single spherical bilayer membrane in suspension

Single spherical bilayer membranes of the Pagano-Thompson type (Pagano, R. and Thompson, T.E. (1967) Biochim. Biophys. Acta 144, 666–669), formed from monooleyl phosphate and cholesterol dissolved in CHCl₃/CH₃OH/n-decane, were subjected to a fast impedance analysis of high precision. Dielectric behavior of the whole system, as monitored from outside the spherical membrane, was sensitive to changes in the membrane state from the thick colored to the thin black state. With a spherical membrane 2–3 mm in diameter formed in the sample cavity containing 0.12 ml 10 mM NaCl, the former state was characterized by a dielectric dispersion having dielectric increment (Δ?) of some 10² and characteristic frequency ($\text{?}{}_{\mathrm{<mtext>c</mtext>}}$) around 10⁶ Hz, while the latter had $\text{Δ? ? 10}{}^5\text{and}\text{?}{}_{\mathrm{<mtext>c</mtext>}}\text{? 10}{}^3\text{Hz}$. Complex plane plots for both dispersions traced semicircles, indicating that the present system may be unequivocally analyzed to yield spherical radius and membrane capacity (C_m) on the basis of a well-established dielectric theory. C_m for the thin membranes has thus been determined to be 0.54 μF · cm^?2, in excellent agreement with a separate determination on planar membranes. The applicability of the present type of spherical membranes under dielectric monitoring to the study of membrane fusion or of exocytosis is suggested.     

The polymorphic phase behaviour and miscibility properties of synthetic phosphatidylethanolamines

(1) The polymorphic phase behaviour of aqueous dispersions of various synthetic phosphatidylethanolamines, both singly and in mixtures, has been investigated by ³¹P-NMR. (2) $\text{14:0}\text{14:0}$ PE remains in the lamellar phase up to 90°C. $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibits a lamellar to hexagonal (H_II) transition between 60°C and 63°C. For $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE, the lamellar to hexagonal (H_II) transition occurs between 7 and 12°C, whereas for $\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}$ PE, the hexagonal (H_II) phase is the preferred structure above ?15°C. (3) Mixtures of $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibit near-ideal miscibility behaviour. For mixtures of $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{14:0}\text{14:0}$ PE there is evidence of fluid-solid immiscibility at temperatures below the gel-liquid crystalline transition temperature of the $\text{14:0}\text{14:0}$ PE component. Mixtures of $\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibit complex phase behaviour involving limited fluid-solid immiscibility at low temperatures and formation of a phase allowing isotropic motional averaging at higher temperatures. (4) ³¹P-NMR provides a graphic method for investigating the miscibility properties of mixed PE systems.     

Comparison of the promoting activity of pristane and n-alkanes in skin carcinogenesis with their physical effects on micellar models of biological membranes

In 1976 (Horton, A.W., Butts, C.K. and Schuff, A.R. (1976) Colloid Interface Sci. 5, 159–168) we assayed pristance (2,6,10,14-tetramethylpentadecane) in a model interfacial system that has given excellent correlation with cocarcinogenic activity among $\text{n-}\text{alkanes}$, as tested in cycloalkane diluents. It was predicted that this branched-chain derivative of the diterpenes would have higher activity than $\text{n-}\text{C}{}_{18}\text{H}{}_{38}$, one of the most cocarcinogenic of the $\text{n-}\text{alkanes}$ in such diluents. Pristane was compared with $\text{n-}\text{C}{}_{18}\text{H}{}_{38}$ and two other $\text{n-}\text{alkanes}$ for their promoting activities in cyclohexane for C3H male mice after a single application of 7,12-dimethylbenz$\text{[a]}\text{anthracene}$. The branched-chain alkane proved to be more active. 20% $\text{n-}\text{tetracosane}$ in cyclohexane was inactive, which correlated with its effects in this diluent in the physical assay system. The promoting activity of 75% $\text{n-}\text{octane}$ in cyclohexane, predicted by the physical assay, was confirmed by tests on mice. The combined by-products of the synthesis of tetracosane, including C₁₂ alkanes and alkenes, C₁₉ and C₂₀ alkylbenzenes, and C₂₄ alkenes, proved to be a very active promoter. However, a mixture in cyclohexane of purified tetracosane with this composite of potential impurities was inactive. From the alkanes behavior in physical systems involving vatious membrane phospholipids and steroids, it is hypothesized that the primary step in their biological activity is a chain-chain interaction with membrane lipids that alters the properties of liquid-crystalline phases at aqueous interfaces. Resulting changes in the microfluidity of the lipid phase and the lateral mobility of critical hormone receptors and enzyme systems, such as the nucleotidyl cyclases, would perturb control systems that maintain the normal behavior of the initiated cell. Thus, its progression to a proliferating neoplasm may be favored.     

The affinity of bacterial polysaccharide-containing fractions for mammalian cell membranes and its relationship to immunopotentiating activity

The natural affinity of various bacterial glycopeptides and lipopolysaccharides for mammalian cell membranes was estimated quantitatively by comparison with the adsorption of lipopolysaccharide from Escherichia coli NCTC 8623 to erythrocytes, thymocytes, bone marrow cells, spleen cells, peritoneal lymphocytes and macrophages. Immunopotentiating activity was estimated by measuring the ability of the bacterial fractions to stimulate a humoral response to ovalbumin in HAM/1CR mice. When the affinity for mammalian cell membranes was compared with the stimulation of the antibody response, it was found that a negative correlation for peritoneal macrophages ($\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{=?0.94, P<0.0005}$) and a positive correlation for peritoneal lymphocytes ($\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{=+0.97,P<0.0005}$) and spleen cells ($\text{r}{}_{\mathrm{<mtext>s</mtext>}}\text{=+0.76,P<0.005}$) existed.     

Catalytic function of thymidylate synthase is confined to S phase due to its association with replitase

Catalytic activity of thymidylate synthase, as measured $\text{in}\text{,}\text{vivo}$, is tightly linked to S phase of the cell cycle in Chinese hamster embryo fibroblast cells. This activity, as measured $\text{in}\text{,}\text{vitro}$, is found in all parts of the cell cycle. Thymidylate synthase activity in nuclear (karyoplast) extracts increased as the cells progressed from $\text{G}{}_0\text{G}{}_1$ to S phase. This enzymatic activity in the nuclei of S phase cells is associated with the multienzyme complex (replitase) that also contained DNA polymerase and other enzymes of DNA replication and precursor synthesis. The degree of association of thymidylate synthase with replitase, which increased co-ordinately as the cells progressed from $\text{G}{}_0\text{G}{}_1$ phase to S phase, coincided strongly with the level of $\text{in}\text{,}\text{vivo}$ activity of the enzyme.     

Soluble and enzymatically stable (Na++K+)-ATPase from mammalian kidney consisting predominantly of protomer αβ-units: Preparation,assay and reconstitution of active Na+, K+transport

Soluble $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$ consisting predominantly of αβ-units with $\text{M}{}_{\mathrm{<mtext>r</mtext>}}$ below 170 000 was prepared by incubating pure membrane-bound $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$ (35–48 μmol P_i/min per mg protein) from the outer renal medulla with the non-ionic detergent dodecyloctaethyleneglycol monoether (C₁₂E₈). $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$ and potassium phosphatase remained fully active in the detergent solution at C₁₂E₈/protein ratios of 2.5–3, at which 50–70% of the membrane protein was solubilized. The soluble protomeric $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$ was reconstituted to Na⁺, K⁺ pumps in phospholipid vesicles by the freeze-thaw sonication procedure. Protein solubilization was complete at C₁₂E₈/protein ratios of 5–6, at the expense of partial inactivation, but $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$ and potassium phosphatase could be reactivated after binding of C₁₂E₈ to Bio-Beads SM2. At C₁₂E₈/protein ratios higher than 6 the activities were irreversibly lost. Inactivation could be explained by delipidation. It was not due to subunit dissociation since only small changes in sedimentation velocities were seen when the C₁₂E₈/protein ratio was increased from 2.9 to 46. As determined immediately after solubilization, $\text{S}{}_{\mathrm{<mtext>20,</mtext><mtext>w</mtext>}}$ was 7.4 S for the fully active $\text{(Na}{}^{\mathrm{+}}\text{+K}{}^{\mathrm{+}}\text{)-ATPase}$, 7.3 S for the partially active particle, and 6.5 S for the inactive particle at high C₁₂E₈/protein ratios. The maximum molecular masses determined by analytical ultracentrifugation were 141 000–170 000 dalton for these protein particles. Secondary aggregation occurred during column chromatography, with formation of enzymatically active $\text{(αβ)}{}_2\text{-}\text{dimers}$ or $\text{(αβ)}{}_3\text{-}\text{trimers}$ with $\text{S}{}_{\mathrm{<mtext>20,</mtext><mtext>w</mtext>}}\text{=10–12}$ S and apparent molecular masses in the range 273 000–386 000 daltons. This may reflect non-specific time-dependent aggregation of the detergent micelles.     

Nuclear magnetic resonance study of the rate of electron transfer between cytochrome c and iron hexacyanides

The rates of electron exchange between ferricytochrome c (C^III)3 and ferrocytochrome c (C^II) were observed as a function of the concentrations of ferrihexacyanide (Fe^III) and ferrohexacyanide (Fe^II) by monitoring the line widths of several proton resonances of the protein. Addition of Fe^II to C^III homogeneously increased the line widths of the two downfield paramagnetically shifted heme methyl proton resonances to a maximal value. This was interpreted as indicating the formation of a stoichiometric complex, C^III·Fe^II, in the over-all reaction:

$\text{C}{}^{\mathrm{III}}\text{+}\text{Fe}{}^{\mathrm{II}}\text{?}\text{k}{}_{\mathrm{?1}}\text{k}{}_1\text{C}{}^{\mathrm{III}}\text{·}\text{Fe}{}^{\mathrm{II}}\text{?}\text{k}{}_{\mathrm{?2}}\text{k}{}_2\text{C}{}^{\mathrm{II}}\text{·}\text{Fe}{}^{\mathrm{III}}\text{?}\text{k}{}_{\mathrm{?3}}\text{k}{}_3\text{C}{}^{\mathrm{III}}\text{+}\text{Fe}{}^{\mathrm{II}}$

Values for $\text{k}{}_1\text{k}{}_{\mathrm{?1}}\text{= 0.4 × 10}{}^3\text{m}{}^{\mathrm{?1}}\text{and}\text{k}{}_2\text{= 208}\text{s}{}^{\mathrm{?1}}$, respectively, were calculated from the maximal change in line width observed at pH 7.0 and 25 °C. Changes in the line width of C^III in the presence of Fe^II and either KCl or Fe^III suggest that complexation is principally ionic, that Fe^III and Fe^II compete for a common site. Addition of saturating concentrations of Fe^III to C^III produced only minor changes in the nuclear magnetic resonance spectrum of C^III suggesting that complexation occurs on the protein surface.Addition of Fe^III to C^II in the presence of excess Fe^II (to retain most of the protein as C^II) increased the line width of the methyl protons of ligated methionine 80. A value for k_?2 ≈ 2.08 × 10⁴ s^?1 was calculated from the dependence of linewidth on the concentration of Fe^II at 24 °C. These rates are shown to be consistent with the over-all rates of reduction and oxidation previously determined by stopped flow measurements, indicating that k₂ and k_?2 were rate limiting. From the temperature dependence the enthalpies of activation are 7.9 and 15.2 kcal/mol for k₂ and k_?2, respectively.