DEGRADATION OF VITELLOGENINS BY 170 KDA TRYPSIN-LIKE PROTEASE IN THE PLASMA OF THE TILAPIA, OREOCHROMIS-NILOTICUS

Proteolytic degradation of plasma vitellogenins during purification pr ocedure has been noted in several teleost fishes. We have characterize d here a trypsin like serine protease in the plasma of the tilapia, Or eochromis niloticus, which degrades vitellogenins. The molecular mass of the protease was estimated as 230 kDa by gel filtration and as 170 kDa both by nondenaturing and by SDS-polyacrylamide gel electrophoresi s. The protease efficiently hydrolyzed the synthetic peptide substrate s for trypsin-like proteases but not the substrates for chymotrypsin l ike proteases nor aminopeptidases. Hydrolysis of the peptide substrate s was strongly inhibited by leupeptin, aprotinin and N-tosyl-L-lysine chloromethyl ketone and to a certain extent by chymostatin, 3,4-dichlo roisocoumarin, phenylmethanesulfonyl fluoride, and soybean trypsin inh ibitor. Leupeptin and aprotinin also inhibited the degradation of a vi tellogenin in the plasma. Although the physiological functions of the 170 kDa protease in vivo have not been elucidated, the results on enzy matic properties of this protease will be useful for the isolation and characterization of vitellogenin not only in tilapia but also in othe r organisms. (C) 1997 Elsevier Science Inc.