A Comparative Examination of Amphibian Sperm Proteolytic Activity

Amphibian sperm proteolytic activity was observed in two ways. In the first method, sperm digested an artificial substrate (gelatin) and in the second, they digested the natural substrate (vitelline coat of the frog egg). When using frog sperm, there was a good correspondence between the results of the two methods, indicating that they are probably measuring the same activity. The order of the reaction intensities was: Rana clamitans ≫ Rana catesbeiana > Rana pipiens ≃ Rana sylvatica. Based on the pattern of cross-fertilizations possible between these species, the proteolytic activity examined is probably required for fertilization. Toad sperm did not digest the frog vitelline coat to the extent that they digested the gelatin. The digestion of the vitelline coat may reflect certain interspecific differences not reflected in the digestion of the gelatin.