SOME PROPERTIES OF THE INTESTINAL PROTEASES OF THE RABBITFISH, SIGANUS-CANALICULATUS (PARK)

Some properties of the intestinal proteases of the rabbitfish were exa mined. At 25 degrees C, both trypsin and chymotrypsin showed pH optima of 8.0. Leucine aminopeptidase, however, displayed maximum activity i n the pH range, 7.0-9.0. Leucine aminopeptidase had the highest optimu m temperature (60 degrees C), and chymotrypsin, the lowest (30 degrees C). The optimum temperature of trypsin was 55 degrees C. The activati on energy, E(a), was found to be 8.24 for trypsin and 8.50 kcal mol(-1 ) for chymotrypsin. The E(a) for leucine aminopeptidase was 6.29 kcal mol(-1) above 40 degrees C and 1.73 kcal mol(-1) below 40 degrees C. S ubstrate concentration-velocity plots showed that all three enzymes fo llowed Michaelis-Menten kinetics; the K-m and V-max were estimated for the three enzymes. The effects of various protease inhibitors on enzy me activity were also examined and confirmed the protease classes to w hich each enzyme belonged. The three proteases examined have similar p roperties to proteases in other fishes.