Biochemistry and Physiology of Oyster Hemocytes Investigation of oyster blood cell lysate revealed one prominent band of proteolytic activity when analyzed using gelatin and collagen impregnated polyacrylamide gel electrophoresis. The proteolytic activity was inhibited by 1,10 Phenanthroline and EDTA, but not by other proteinase inhibitors. Maximal activity was shown at pH 8.2 and the molecular weight of the protein responsible for the activity was estimated to be 68 kDa. Proteolytic activity was also measured by fluorescence assays containing hemocyte lysate and fluorescein-labeled gelatin, type I or type IV collagen. Characteristics of this proteolytic activity suggest that an invertebrate matrix metalloproteinase is responsible.