Photosynthetic electron transport, ATP synthesis and nitrogenase activity in isolated heterocysts of Anabaena cylindrica.

Isolated heterocysts of the N2-fixing blue-green alga Anabaena cylindrica contain the Photosystem I components P-700, bound and soluble ferredoxins and ferredoxin-NADP reductase. They also show Photosystem I activity being able to photoreduce both methylviologen and NADP when ascorbate + dichlorophenol-indophenol acts as reductant. They photophosphorylate (64 munol ATP produced/mg chlorophyll a/h) and carry out oxidative phosphorylation (8.7 munol ATP produced/mg chlorophyll a/h). Ninety per cent of the total cell-free extract nitrogenase activity is located in the heterocyst fraction of aerobic cultures.