Effect of Monochromatic Light on Proton Efflux of the Blue-Green Alga Anabaena variabilis

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Abstract
Light-induced proton efflux of Anabaena variabilis was found to be biphasic, the second phase being inhibited by the ATPase inhibitor nitrofen (2,4-dichloro-1-[4-nitrophenoxy]benzene).The first, fast phase was triggered by monochromatic light of 707 nanometers, whereas the second, slower phase was not. With 707 nanometers, light, respiratory O2 uptake was inhibited. Using light composed oftwo wavelengths (616 and 707 nanometers) a marked enhancement of both O2 evolution as well as the second phase of proton efflux was observed. The first phase was not enhanced. Thus, phase II is driven by both photosystems. As concluded from the action spectrum phase I is markedly determined by photosystem-I activity. Altogether the data show that two different mechanisms of light-induced proton efflux exist on the cytoplasmic membrane of Anabaena, the slower one being dependent on ATP and linear photosynthetic electron flow.