Abstract
Spheroplasts of a Synechococcus sp. thermophilic cyanobacterium showed cyclic photophosphorylation activity of 1200μmolATP/mg Chlh at 45 C with ascorbate-phenazine methosulfate, and non-cyclic activity of 11μmol ATP/mg Chl h with H2O-methyl viologen. Thylakoid membranes exhibited less than one-tenth of the spheroplasts activities in both types of photophosphorylation. The spheroplasts gave optimal cyclic phosphorylation at 55°C and lost half of the activity at 67°C for 5min. It was suggested that the stability of the photosynthetic membranes to retain proton gradient across the membranes might be closely related to the thermostability of the photophosphorylation.
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