The cytochrome c binding site on cytochrome c oxidase.

Cytochrome $\text{c}$ was chemically coupled to cytochrome $\text{c}$ oxidase using the reagent 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) which couples amine groups to carboxyl residues. The products of this reaction were analyzed on 2.5–27% polyacrylamide gradient gels electrophoretically. Since cytochrome $\text{c}$ binds to cytochrome oxidase electrostatically in an attraction between certain of its lysine residues and carboxyl residues on the oxidase surface, EDC is an especially appropriate reagent probe for binding-subunit studies. Coupling of polylysine to cytochrome oxidase using EDC was also performed, and the products of this reaction indicate that polylysine, an inhibitor of the cytochrome $\text{c}$ reaction with oxidase, binds to the same oxidase subunit as does cytochrome $\text{c}$, subunit IV in the gel system used.     

Cross-linking studies on a cytochrome c-cytochrome c oxidase complex.

A cytochrome $\text{c}$ - cytochrome $\text{c}$ oxidase complex containing 0.8–1.0 moles of cytochrome $\text{c}$ per mole of cytochrome $\text{c}$ oxidase (heme a + a₃) was isolated as described by Ferguson-Miller, S., Brautigan, D.L., and Margoliash E., J. Biol. Chem. $\text{251}$, 1104 (1976). This complex was reacted with dithiobissuccinimidyl propionate, an 11 Å bridging bifunctional reagent, and the cross-linked products obtained were analyzed by two dimensional gel electrophoresis. Cytochrome $\text{c}$ was cross-linked to subunit II of cytochrome $\text{c}$ oxidase. Other cross-linked products were formed involving different subunits of cytochrome $\text{c}$ oxidase. These included I+V, II+V, III+V, V+VII, IV+VI and IV+VII. Experiments are also described using N,N′-bis(3-succinimidyloxycarbonylpropyl) tartarate. The major product formed with this 18 Å bridging bifunctional reagent was a pair containing II+VI.     

Binding of cytochrome c to the cytochrome bc1 complex (complex III) and its subunits cytochrome c1 and b1.

Cytochrome $\text{c}$₁, the electron donor for cytochrome $\text{c}$, is a subunit of the mitochondrial cytochrome $\text{bc}$₁ complex (complex III, cytochrome $\text{c}$ reductase). To test if cytochrome $\text{c}$₁ is the cytochrome $\text{c}$-binding subunit of the $\text{bc}$₁ complex, binding of cytochrome $\text{c}$ to the complex and to isolated cytochrome $\text{c}$₁ was compared by a gel-filtration method under non-equilibrium conditions (a $\text{bc}$₁ complex lacking the Rieske ironsulfur protein was used; von Jagow et al. (1977) Biochim. Biophys. Acta $\text{462}$, 549–558). The approximate stoichiometries and binding affinities were found to be very similar. Binding of cytochrome $\text{c}$ to isolated cytochrome $\text{b}$ which is another subunit of the reductase was not detectable by the gel-filtration method. Further, the same lysine residues of cytochrome $\text{c}$ were shielded towards chemical acetylation in the complexes $\text{c}\text{:}\text{c}$₁ and $\text{c}\text{:}\text{bc}$₁. From this we conclude that the same surface area of cytochrome $\text{c}$ is in direct contact with cytochrome $\text{bc}$₁ and with cytochrome $\text{c}$₁ in the respective complexes and that therefore cytochrome $\text{c}$ is most probably the structural ligand for cytochrome $\text{c}$ in mitochondrial cytochrome $\text{c}$ reductase.     

Isolation and properties of the cytochrome B-C1 complex from Rhodopseudomonas sphaeroides

A highly purified and active cytochrome $\text{b}$-$\text{c}$₁ complex has been isolated from the chromatophores of the photosynthetic bacteria $\text{Rhodopseudomonas}\text{sphaeroides}$ R-26, through steps of Triton X-100 solubilization, salt fractionation and calcium phosphate column chromatography. The isolated enzyme complex catalyzes fully antimycin A sensitive oxidation of ubiquinol by cytochrome $\text{c}$ with a turnover number of 1500 per minute at 23° based on cytochrome $\text{c}$₁. It contains 8.3 nmoles of cytochromes $\text{b}$ and $\text{c}$₁ per mg protein and shows four polypeptides in the sodium dodecylsulfate polyacrylamide gel electrophoresis.     

A Novel function of cytochrome C (555, Chlorobium thiosulfatophilum) in oxidation of thiosulfate

Thiosulfate-cytochrome c-551 reductase derived from $\text{Chlorobium}\text{thiosulfatophilum}$ has been highly purified. The enzyme reduces cytochrome $\text{c}\text{-551 of}\text{C}\text{.}\text{thiosulfatophilum}$ in the presence of thiosulfate while cytochrome $\text{c}$-555 of the organism is not reduced by the enzyme. Cytochrome $\text{c}$-555 reacts with the enzyme at an appreciable rate only in the presence of cytochrome $\text{c}$-551. However, the reduction rate of cytochrome $\text{c}$-551 by the enzyme is greatly enhanced on addition of a catalytic amount of cytochrome $\text{c}$-555. Therefore, cytochrome $\text{c}$-555 seems to function as an effector on thiosulfate-cytochrome $\text{c}$-551 reductase as well as it acts as the electron donor to the light-excited chlorobium chlorophylls.     

Cytochrome oxidase from an extreme thermophile. Thermus thermophilus HB8

The cytochrome oxidase (EC 1.9.3.1) of $\text{Thermus}\text{thermophilus}$ HB8 was isolated from the membrane fraction, and was highly purified. The oxidase contained heme $\text{a}$ and heme $\text{c}$ as the prosthetic groups. The purified preparation showed a single band in polyacrylamide gel electrophoresis, and three major polypeptides with apparent molecular weights of 52,000, 37,000 and 29,000 were observed in the presence of sodium dodecyl sulfate. The enzyme reacted rapidly with $\text{T}\text{.}\text{thermophilus}$ cytochrome c-552. The oxidation of $\text{T}\text{.}\text{thermophilus}$ cytochrome $\text{c}$-555,549 by the enzyme was very slow, and was stimulated by the addition of cytochrome $\text{c}$-552. The enzyme was highly stable to heat.     

Purification of cytochrome P-450 from liver microsomes of phenobarbital-treated guinea pigs

Cytochrome P-450 was purified from phenobarbital-treated guinea pigs to a specific content of 19.8 nmoles per mg of protein, and was free of cytochrome b₅ and NADPH-cytochrome $\text{c}$ reductase. The purified cytochrome P-450 gave a single protein band on sodium dodecylsulfate-polyacrylamide gel electrophoresis, and an apparent molecular weight of about 49,000 was estimated. Benzphetamine N-demethylation activity could be reconstituted by mixing the purified cytochrome, NADPH-cytochrome $\text{c}$ reductase and phosphatidylcholine.     

Cobalt cytochrome c: enzymic assays.

An improved synthesis for cobalt-cytochrome $\text{c}$ has been developed; its half reduction potential is ?140 ± 20mV. Reduced ^Cocyt-$\text{c}$³ is oxidized by bovine heart cytochrome $\text{c}$ oxidase at a rate ～45% that of the native cytochrome $\text{c}$. It is not reduced by mitochondrial NADH or succinate cytochrome $\text{c}$ reductase nor by microsomal NADH or NADPH cytochrome $\text{c}$ reductase.     

The presence of multiple cytochrome b proteins in succinate-cytochrome c reductase.

Two cytochrome $\text{b}$ proteins were isolated from succinate-cytochrome $\text{c}$ reductase and the cytochrome $\text{b-c}{}_1$ complex. Their molecular weights were determined to be 37,000 and 17,000 daltons by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Spectral properties and amino acid composition of these two proteins are reported in the paper.     

Binding of cytochrome c to cytochrome c-oxidase in intact mitochondria. A study with radioactive photoaffinity-labeled cytochrome c

[³H]-p-Azidophenacylbromide-(methyl-4-mercaptobutyrimidate)-cytochrome $\text{c}$ from $\text{Saccharomyces cerevisiae}$ was prepared and its properties determined. The radioactive photoaffinity-labeled cytochrome $\text{c}$ was linked by irradiation into a covalent complex with cytochrome $\text{c}$ oxidase. Analysis of the complex on SDS-polyacrylamide gels showed that cytochrome $\text{c}$ bound to one of the smaller subunits of cytochrome $\text{c}$ oxidase with an apparent molecular weight of 15,000.     

Purification and some properties of cytochrome C553(550) isolated from Desulfovibrio desulfuricans Norway.

A new c-type cytochrome containing a single heme group, cytochrome c_553(550) has been purified from $\text{Desulfovibrio desulfuricans}$ (Norway strain) and some of its properties have been investigated. It has an isoelectric point of 6.6 and a higher redox potential than cytochrome c₃ isolated from the same bacteria. Its molecular weight was estimated to be 9,200 by gel filtration. The main absorption peaks are at 553, 522.5 and 417 nm in the reduced form and at 690, 529, 411, 357 and 280 nm in the oxidized form. The asymmetric α band of the reduced state is similar to the one reported for socalled “split α” cytochromes c. The cytochrome contains 86 amino acid residues with 5 methionine, two cysteine and two histidine residues. The N terminal sequence of $\text{D. desulfuricans}$ Norway cytochrome c_553(550) presents no evident homology with that of $\text{Desulfovibrio vulgaris}$ Hildenborough cytochrome c₅₅₃.     

Immunoassay for honey bee cytochrome c in single animals with cytochrome c-coated bacteriophages: A sensitive tool for the study of caste formation in the honey bee, Apis Mellifera

The development of a sensitive viroimmunoassay for honey bee cytochrome $\text{c}$ and its usage for early detection of caste differentiation is described. Pure honey bee cytochrome $\text{c}$ was isolated from workers and used to produce antibodies in rabbits. Bacteriophage T4 was chemically modified by covalent attachment of honey bee cytochrome $\text{c}$ using tolylene-2,4-diisocyanate as a cross-linking agent. The immunospecific inactivation of this bacteriophage-cytochrome c conjugate by anti-cytochrome $\text{c}$ antibodies can be inhibited by free cytochrome $\text{c}$. In quantitative determinations, 50% inhibition is reproducibly achieved at a concentration of 6 ng/ml (5 pmol/ml) and as little as 0.3 ng/ml (0.25 pmol/ml) could be detected by this system. Cytochrome $\text{c}$ concentrations were measured in individual animals and substantial differences between corresponding larval stages of worker and queen bees are reported.     

A new photoaffinity-labeled derivative of mitochondrial cytochrome c

Three lysine residues of horse heart cytochrome $\text{c}$ were modified by reaction with methyl-4-mercaptobutyrimidate hydrochloride and the free SH group of the latter was covalently linked to p-azidophenacyl bromide yielding a photoaffinity-labeled cytochrome $\text{c}$. The photoaffinity-labeled cytochrome $\text{c}$ was bound by irradiation into a covalent complex with cytochrome $\text{c}$ oxidase.     

Selectivity of oxidase and reductase activity of horse heart cytochrome c

The ascorbate-TMPD-cytochrome $\text{c}$ oxidase and succinate cytochrome $\text{c}$ reductase activities and the redox potentials of native and chemically modified cytochromes $\text{c}\text{—NBS-cytochrome}\text{c}$ with modification of Trp-59 and Met-65, nitro-cytochrome $\text{c}$ with modification of Tyr-67, and a new preparation, Chloramine-T-cytochrome m$\text{c}$ with modification of Met-80 and -65 to methionine sulfoxide—have been compared at pH 7.8 in 25 mM cacodylate-Tris buffer. These modifications exhibit (i) a slight lowering of redox potential, from 260 mV to 180, 215 and 170 mV, respectively, (ii) destabilization of the cytochrome $\text{c}$-reductase complex, 6 to 12 fold, but without alteration of the cytochrome $\text{c}$-oxidase complex, and (iii) a slight lowering of the maximum velocity for both the oxidase and reductase reactions. The selective destabilization of the cytochrome $\text{c}$-reductase complex is interpreted as an indication of a two-path, two-function model for the oxido-reduction function of cytochrome $\text{c}$.     

Isolation of QP-C and reconstitution of the QH2-c reductase

A ubiquinone protein, QP-C, which acts in the cytochrome $\text{b}\text{-}\text{c}$₁ region has been solubilized. The isolated QP-C shows one band of molecular weight 15,000 in polyacrylamide gel electrophoresis in sodium dodecyl sulfate and isoelectric focusing at the isoelectric point of pH 3.6. QP-C reconstitutes with the QP-C deficient $\text{b}\text{-}\text{c}$₁ complex to restore the OH₂-cytochrome $\text{c}$ activity and recover the EPR signal of the complex.     

Reversible redox titrations of cytochrome c and cytochrome c oxidase using detergent solubilized electrochemically generated mediator-titrants

The repetitive, $\text{reversible}$ equilibrium redox cycling of cytochrome $\text{c}$, cytochrome $\text{c}$ oxidase, or mixtures thereof has been made possible by the use of the oxidant, ferricinium ion. This ion is electrochemically generated by the use of non-ionic detergent solubilized ferrocene which is apparently incorporated as micelles and readily electron transfers with an electrode. The $\text{ferricinium-ferrocene}$ couple equilibrates rapidly with these heme proteins. Electrochemically generated benzylviologen radical cations are used as the reductant. The E^O′ values for cytochrome $\text{c}$ oxidase at pH 7.0 are 209 ± 15 mv (2e^?) and 340 ± 15 mv (2e^?).     

EPR study of the effect of formate on cytochrome C oxidase

The addition of formate to oxidized cytochrome $\text{c}$ oxidase (ferrocytochrome $\text{c}$: oxygen oxidoreductase, EC 1.9.3.1) causes the appearance of a high spin heme signal at g = 6 and a splitting of g = 3 signal to g = 2.98 and 3.07. When formate-cytochrome $\text{c}$ oxidase is reduced, the g = 2.98 signal decreases significantly. The spectrophotometric studies showed that formate is a specific ligand to cytochrome $\text{a}$₃. Data suggest that binding of formate to oxidized cytochrome $\text{c}$ oxidase produces a ligand-$\text{a}$₃ interaction leading to the splitting of g = 3 signal hitherto considered as due to cytochrome $\text{a}$. Thus both cytochrome $\text{a}$ and $\text{a}$₃ contribute to the resonance of g = 3 signal of cytochrome $\text{c}$ oxidase.     

Resonance Raman spectroscopy of cytochrome c oxidase and electron transport particles with excitation near the Soret band

We report the resonance Raman spectra of cytochrome $\text{c}$ oxidase, both solubilized and in electron transport particles using laser excitation near the Soret band. As in the spectra of other hemoproteins, such as cytochrome $\text{c}$, the shape and intensity of a number of bands change when the oxidation state is varied. However, one of the hemes of solubilized cytochrome $\text{c}$ oxidase shows redox behavior which is anomalous. Spectra of electron transport particles are dominated by cytochrome $\text{c}$ oxidase. There are, however, definite differences between spectra of solubilized cytochrome $\text{c}$ oxidase and electron transport particles in the oxidized states.     

A gel-electrophoretically homogeneous preparation of cytochrome P-450 from liver microsomes of phenobarbital-pretreated rabbits

Cytochrome P-450 was purified from liver microsomes of phenobarbital-pretreated rabbits to a specific content of 16 to 17 nmoles per mg of protein with a yield of about 10 %. The purified cytochrome yielded only a single protein band on sodium dodecylsulfate-urea-polyacrylamide gel electrophoresis, and an apparent molecular weight of about 45,000 was estimated for the protein. The preparation was free of cytochrome $\text{b}{}_5$, NADH-cytochrome $\text{b}{}_5$ reductase, and NADPH-cytochrome $\text{c}$ reductase activities. Aniline hydroxylase and ethylmorphine N-demethylase activities could be reconstituted upon mixing the purified cytochrome with an NADPH-cytochrome $\text{c}$ reductase preparation (purified by a detergent method) and phosphatidyl choline.     

Photoreduction of membrane bound cytochrome C by excited-state phenothiazine.

Ferricytochrome $\text{c}$ can be reduced in a photochemical reaction by excited state phenothiazine. This reaction is observed between phenothiazine which is solubilized by phospholipid artificial membranes and cytochrome $\text{c}$ which is adsorbed to the membrane surface. Under conditions when cytochrome $\text{c}$ is not bound to the phospholipid, the rate of reduction by phenothiazine is greatly reduced. The phosphorescence of phenothiazine is quenched in the presence of cytochrome $\text{c}$, implying that the excited triplet state interacts with cytochrome $\text{c}$. Oxygen inhibits the reaction since possibly, as a paramagnetic species, it increases intersystem crossing of the excited states of phenothiazine. On the basis of molecular models the proximity between the iron of ferricytochrome $\text{c}$ and phenothiazine is estimated to be over 20 Å.