Further investigation of the light-induced cytochrome b-559 reaction in membrane fragments of the blue-green alga Anabaena variabilis

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Abstract
Oxidation-reduction reactions of the low redox potential cytochrome b-559 were studied for membrane fragments of the blue-green alga Anabaena variabilis. Cytochrome photooxidation was observable at room temperature when the membrane fragments had been preincubated at room temperature in the dark. A CCCP addition (10−4M) strongly enhanced the reaction. Oxidation consisted of a DCMU-sensitive and an insensitive reaction. The former depended on actinic illumination of short wavelength. The latter showed a dependency on longer wavelength light. The former was assumed to be induced by the action of photosystem II and the latter by that of photosystem I. The photosystem II oxidation was small before preincubation, and was enhanced by added DPIP or Ferro. This was interpreted as photosystem II action inducing oxidation as well as reduction; reduction being inactivated during dark incubation or being suppressed by added redox reagents which compete for electron acceptance from photosystem II so that oxidation was apparently enhanced. The oxidationreduction reactions of this cytochrome with low redox potential were assumed to be almost identical with those of the high redox potential form, at least in the membrane fragments of Anabaena variabilis.

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