Respiration in energy-transducing membranes of the thermophilic cyanobacterium Mastigocladus laminosus: II. Oxidative phosphorylation

Oxidative phosphorylation was measured in isolated energy-transducing membranes of the thermophilic cyanobacterium Mastigocladus laminosus with NADH-mediated electron transport. This dark phosphorylation was similar to photophosphorylation in its sensitivity to uncouplers and energy-transfer inhibitors. However, photophosphorylation was 20- to 50-times more active than oxidative phosphorylation. The $\text{P}\text{O}$ ratio of oxidative phosphorylation was about 0.2. Besides oxidative phosphorylation, adenylate kinase- and ADP-P_i exchange activity were measured in the dark. The ADP-P_i exchange reaction was identified as polynucleotide phosphorylase.