Previously, it has been reported that NADH cytochrome c reductase and succinate cytochrome c reductase, in which the redox reaction in cytochrome b is involved, are activated by light irradiation with peaks of photo-activation at wavelengths of 430, 530 and 570 nm corresponding to those in the absorption spectrum of reduced cytochrome b in mitochondria isolated from sperm of echiuroid, oyster and sea urchin (Tazawa et al., 1996). In sperm of these species, augmentation of respiration due to photo-activation of the cytochrome b reaction is observed only when the electron transport in this span of the mitochondrial respiratory chain is inhibited by carbon monoxide (Fujiwara et al., 1991; Yasumasu et al., 1991) or by a decrease in the amount of cytochrome b due to sperm ageing. In sperm cultured for a long time, the respiratory rate was very low and almost all sperm became immotile. In these sperm, respiration was reactivated by light irradiation at the wavelengths of 430, 530 and 570 nm (Fujiwara et al., 1999).

In the present study, photo-reactivation of movement in these somewhat degenerated sperm incubated for a long time was also found to occur, with peaks at the above-mentioned wavelengths. We concluded that photo-reactivation of movement in these sperm, in which the cytochrome b reaction probably became rate-limiting in the respiration chain, is supported by reactivation of respiration by light irradiation. On the other hand, though the ATP level decreased to a rather low level at about 30 min after the initiation of incubation in sperm of all species examined, sperm swam for more than 10 h, by which time the ATP level was quite low. Light irradiation induced reactivation of movement but did not alter the rather low ATP level in these sperm. Thus the ATP level does not seem to be responsible for making sperm immotile. In sperm treated with Triton X-100, movement was induced by adding ATP and Mg2+, even when many sperm had become immotile after a long incubation. Hence, capacity for movement does not seem to be reduced by a long incubation time. The movement of sperm treated with Triton X-100 was not activated bv light irradiation.