Effect of NADP + on light-induced cytochrome changes in membrane fragments from a blue-green alga

Abstract

The effect of NADP + on light-induced steady-state redox changes of membrane-bound cytochromes was investigated in membrane fragments prepared from the blue-green algae Nostoc muscorum (Strain 7119) that had high rates of electron transport from water to NADP + and from an artificial electron donor, reduced dichlorophenolindophenol (DCIPH 2) to NADP +. The membrane fragments contained very little phycocyanin and had excellent optical properties for spectrophotometric assays. With DCIPH 2 as the electron donor, NADP + had no effect on the light-induced redox changes of cytochromes: with or without NADP +, 715- or 664-nm illumination resulted mainly in the oxidation of cytochrome f and of other component(s) which may include a c-type cytochrome with an α peak at 549 nm. With 664 nm illumination and water as the electron donor, NADP + had a pronounced effect on the redox state of cytochromes, causing a shift toward oxidation of a component with a peak at 549 nm (possibly a c-type cytochrome), cytochrome f, and particularly cytochrome b 559. Cytochrome b 559 appeared to be a component of the main noncyclic electron transport chain and was photooxidized at physiological temperatures by Photosystem II. This photooxidation was apparent only in the presence of a terminal acceptor (NADP +) for the electron flow from water.