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  • Title: Interaction of integral and peripheral membrane proteins: affinity labeling of yeast cytochrome oxidase by modified yeast cytochrome c.
    Author: Birchmeier W, Kohler CE, Schatz G.
    Journal: Proc Natl Acad Sci U S A; 1976 Dec; 73(12):4334-8. PubMed ID: 188034.
    Abstract:
    To identify possible substrate-binding subunit(s) of yeast cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1-9-3-1), the purified enzyme was reacted with yeast iso-1-cytochrome c whose single free sulfhydryl group at position 107 had been activated with 5,5'-dithiobis(2-nitrobenzoate). The resulting cytochrome c derivative appeared to function as an "affinity-label" of cytochrome oxidase, since it rapidly inactivated the enzyme. Inactivation was competitively prevented by underivatized cytochrome c. When the "affinity-labeled" oxidase was analyzed by two-dimensional polyacrylamide electrophoresis in dodecyl sulfate (separation in the second dimension being carried out in the presence of excess sulfhydryl compound), it was found that the derivatized cytochrome c had specifically formed a mixed disulfide with the mitochondrially made subunit III (apparent molecular weight 24,000) of the oxidase. Similar results were obtained when underivatized iso-I-cytochrome c was crosslinked to the oxidase by oxidative disulfide bridge formation in the presence of ortho-phenanthroline and Cu++. These data indicate that the hydrophobic mitochondrially made subunit III of yeast cytochrome c oxidase is in close proximity to the cytochrome c binding site on the enzyme. Since cytochrome c and the mitochondrially made cytochrome oxidase subunit III are typical peripheral and integral membrane proteins, respectively, the present study suggests a useful approach for analyzing specific interactions between these different classes of membrane proteins.
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