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 giga s) oysters were compared for levels of inhibitory activities against a vari ety of proteases. Representatives of the serine, cysteine, metallo and aspa rtic protease mechanistic classes were analyzed, including extracellular pr oteases produced by two oyster-associated pathogens; Perkinsus marinus and Vibrio io vulnificus. In comparison to C. virginica, C. gigas plasma exhibi ted 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 thermol ysin only. A similar trend was noted for thermolysin with the eastern oyste r samples. These studies indicate the presence of protease inhibitors in th e plasma of Crassostrea spp., which may have an impact upon host defense me chanisms, in addition to other physiological roles. (C) 1998 Elsevier Scien ce Inc. All rights reserved.