Light irradiation, at a light fluence rate sufficient for the strong photo-reactivation of the CO-inhibited cytochrome c oxidase in mitochondria isolated from the sperm of fish, oyster and sea urchin, weakly activated the CO-inhibited respiration only in the sea urchin sperm, with peaks of photo-reactivation corresponding to those in the absorption spectrum of CO-bound cytochrome aa3. NADH cytochrome c reductase was inhibited by CO, weakly in mitochondria from sea urchin sperm and completely in those from fish and oyster sperm. The CO-induced complete inhibition of cytochrome c reduction in fish and oyster sperm probably does not allow the photo-reactivation of CO-inhibited cytochrome c oxidase to augment CO-blocked respiration. At a light fluence rate higher than that mentioned above, photo-activation of NADH cytochrome c reductase, found in the sperm of oyster and sea urchin, occurred even in the presence of CO in mitochondria isolated from sea urchin sperm and strongly activated CO-inhibited respiration in sea urchin sperm, with peaks corresponding to those in the absorption spectrum of reduced cytochrome b. The acceleration of cytochrome c reduction due to the photo-activation of this complex enzyme in sea urchin sperm probably induces another activation of CO-inhibited respiration at the high light fluence rate.
