Enzymatic reduction of algal cytochrome f

Abstract

Summary The purified f-type cytochrome 553 of the alga Bumilleriopsis filiformis Vischer (Xanthophyceae) is used as electron acceptor (from NADPH) in a diaphorase system with ferredoxin-NADP reductase (E.G. 1.6.7.1; 1.6.1.1) and with and without ferredoxin of the alga present in the assay. Some enzymatic criteria of the system and of the algal cytochrome 553 in particular are thereby described. The latter is compared in this respect with mammalian cytochrome c: a) There is a substantial reactivity of cytochrome 553 with the reductase, ferredoxin not being necessary. b) Ferredoxin stimulates reduction about 10 times in case of cytochrome 553 and 80 to 90 times with mammalian cytochrome c at a common pH optimum of about 7. The Km is 0.5 μM ferredoxin with cytochrome 553 used as the terminal electron acceptor and 1.72 μM ferredoxin with cytochrome c. c) The superoxide radical is important only in cytochrome c reduction without ferredoxin present. Ferredoxin abolishes the effect of oxygen during cytochrome reduction. d) Furthermore, details of substitution of ferredoxin by potassium ferrocyanide are given and the influence of reduced thionicotinamide-NADP on cytochrome reduction.