Abstract
In sperm of the echiuroid, Urechis unicinctus, respiration in the presence of CO was reversibly augmented by light irradiation in an examined range of wavelengths between 350 and 650 nm. The respiratory rate of sperm in the presence of CO was enhanced by light irradiation in proportion to the light fluence rate. A sharp and large peak was obtained at the wavelength of 430 nm in the action spectrum of photo-activated respiration of sperm in the presence of CO. Broad and small peaks were also found at around 530 and 570 nm. This action spectrum is similar in its profile to the absorption spectrum of reduced cytochrome b. Absorption ofphoton energy by reduced b-type cytochrome probably activates the redox reaction of this cytochrome to enhance the respiratory rate. Photo-activated respiration in the presence of CO was inhibited by antimycin A and cyanide. In this respiratory system, an electron equivalent is probably transferred through the mitochondrial respiratory chain between cytochrome b and cytochrome c and finally to molecular oxygen in the reaction catalyzed by the CO-insensitive terminal oxidase.
