Evidence for the presence of protease inhibitors in eastern (Crassostrea virginica) and Pacific (Crassostrea gigas) oysters

The plasma of eastern (Crassostrea virginica) and Pacific (Crassostrea gigas) oysters were compared for levels of inhibitory activities against a variety of proteases. Representatives of the serine, cysteine, metallo and aspartic protease mechanistic classes were analyzed, including extracellular proteases produced by two oyster-associated pathogens; Perkinsus marinus and Vibrio io vulnificus. In comparison to C. virginica, C. gigas plasma exhibited significantly higher specific inhibition levels (ng protease inhibited/mu g plasma protein) for papain (P < 0.001), pepsin (P < 0.001), P. marinus protease (P < 0.001), trypsin (P = 0.015), and V. vulnificus protease (P <0.001). Plasma of C. gigas did not inhibit the metalloprotease thermolysin. Instead, a significant increase in substrate hydrolysis was seen in wells containing plasma and thermolysin in comparison to wells containing thermolysin only. A similar trend was noted for thermolysin with the eastern oyster samples. These studies indicate the presence of protease inhibitors in the plasma of Crassostrea spp., which may have an impact upon host defense mechanisms, in addition to other physiological roles. (C) 1998 Elsevier Science Inc. All rights reserved.