PROTEASE INHIBITORS, LEUPEPTIN AND ANTIPAIN, STIMULATE THE RESPIRATION OF SEA URCHIN SPERM

Respiration of sperm of the sea urchin, Anthocidaris crassispina, suppressed at pH 6.8, was enhanced to the level in normal seawater (pH about 8.2) by 0.3 mM leupeptin or 0.58 mM antipain in a Na+- and Mg2+-dependent manner. Leupeptin acid (Ac-Leu-Leu-Arg) devoid of protease inhibitor activity, Nα-p-tosyl-L-lysine chloromethyl ketone (TLCK) and benzamidine also stimulated respiration moderately, whereas soybean trypsin inhibitor, p-aminobenzamidine, Nα-p-tosyl-L-arginine methyl ester (TAME), a synthetic substrate for trypsin, and L-arginine were almost without effect. Effects of several other microbial protease inhibitors were also investigated. Leupeptin and antipain seem to stimulate the sperm respiration by a mechanism not associated with protease activity. These inhibitors did not induce the acrosome reaction at pH 6.8.