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J. Biochem, 1988, Vol. 103, No. 5 755-758
© 1988 Japanese Biochemical Society

research-article

Enzymatic Properties of Ubiquinol: Cytochrome c2 Oxidoreductase In Situ in Rhodopseudomonas palustris Membranes1

Ken-ichiro Takamiya, Faculty of Science

Department of Biology,Kyushu University Higashi-ku, Fukuoka, Fukuoka 812

The presence of ubiquinol: cytochrome c2 oxidoreductase was shown in the membranes from a photosynthetic bacterium, Rhodopseudomonas palustris. Some properties of the enzyme in situ were investigated. The optimal pH of this enzyme activity was 7.0 in the intact membranes. The activity was inhibited by both antimycin and myxothiazol. Maximal activity (Vmax) was 3–4 mol cytochrome c (c2) reduced/mol cytochrome c1.s. Apparent activity of the enzyme with horse heart cytochrome c as the electron acceptor decreased as the concentration of salts in the reaction mixture increased, whereas when R. palustris cytochrome c2 was used as the electron acceptor, the activity increased as the concentration of salts increased. Moreover, the activity of the enzyme did not depend on the species or concentration of anions but on both the concentration and valency of the cations of the salts. These salt effects were thought to be due to the change of effective concentration of cytochrome molecules caused by cations near the membrane surface, which was net negatively charged. Apparent Km for ubiquinol-1 was about 80 µM irrespective of the species of cytochrome and the presence of salts.

1This work was supported in part by a Grant-in-Aid from the Ministry of Education, Science and Culture of Japan.


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