Terminal Oxidases of Chlorella pyrenoidosa.

In studies of the kinetics of oxygen uptake by glucose-stimulated Chlorella pyrenoidosa, two terminal oxidases could be distinguished. The cytochrome oxidase of Chlorella has a Km (O(2)) of 2.1 +/- 0.3 mum, while the second oxidase has a Km (O(2)) of 6.7 +/- 0.5 mum, and a maximum capacity about one-quarter of that of the cytochrome system. The identity of the second oxidase is unknown, but it is not inhibited by carbon monoxide, 1 mm cyanide, 0.1 mm thiocyanate, or 1 mm 8-hydroxyquinoline. In fresh cultures, the second oxidase accounts for at most 35% of the total oxygen uptake.