Stoichiometric Photophosphorylation in Thylakoids from the Blue-Green A\ga, Anabaena variabilis

A method is described for the preparation of thylakoids from the blue-green alga Anabaena variabilis which exhibit photosynthetic control. The thylakoids can be stored in liquid N 2 with little loss in activity. P /e2 ratios (number of ATP molecules formed per pair of electrons transported) have been determined for partial reactions of the photosynthetic electron transport chain. Electron transport from water to an electron acceptor of photosystem I is coupled to phos­ phorylation with a P /e2 ratio of 0.9— 1.2, from water to electron acceptors of photosystem II with ratios of 0 .21-0.3, and oxidations of hydrogen carriers by photosystem I with ratios of 0.3 — 0.35. Electron transport in these assay systems generates a proton gradient across the thylakoid mem­ brane (acid inside), which is decreased by the substrates of phosphorylation and by uncouplers.