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 $\text{K}m(\text{O}_{2})$ of 2.1 ± 0.3 μM, while the second oxidase has a $\text{K}m(\text{O}_{2})$ of 6.7 ± 0.5 μM, 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.