Chymotrypsin-like protease activity associated with demembranated sperm of chum salmon

Our previous study suggested that a chymotrypsin-like protease was involved in the motility of chum salmon sperm (Inaba K, Morisawa M, Biomed Res (1991) 12, 435-437). In this study, we examined the peptidase activity of demembranated sperm of chum salmon using ten synthetic peptides. When spermatozoa were treated with 0.04% Triton X-100 for extracting the plasma membrane and the suspension was separated into the Triton-soluble and insoluble fractions by centrifugation, only the hydrolytic activity towards succinyl (Suc)-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide (MCA), a typical substrate for chymotrypsin-like protease, was mostly retained in the insoluble fraction. The bulk of the activities toward other substrates was detected in the soluble fraction. Flagellar axonemes isolated from demembranated sperm showed considerable hydrolytic activity toward Suc-Leu-Leu-Val-Tyr-MCA and the activity was still retained in the axoneme even after further washing. The hydrolysis was activated by a low concentration of SDS, suggesting that the protease associated with the axonemes is a multicatalytic ATP-dependent proteinase (proteasome). Motility of demembranated sperm was inhibited by Suc-Leu-Leu-Val-Tyr-MCA in an ATP-concentration-dependent manner. These results suggest that proteasomes associated with flagellar axoneme regulate flagellar motility.