Hemocyte components in crustaceans convert hemocyanin into a phenoloxidase-like enzyme

The functional conversion of hemocyanin (He), an oxygen transporter, into an enzyme was investigated in crustaceans. He is converted into a phenoloxidase-like enzyme by hemocyte components, which is triggered by beta-1,3-glucan. This activation is severely hampered with leupeptin and E-64 treatment, indicating that the serine/cysteine proteases in the hemocytes are involved in the activation. In a SDS-PAGE-analysis, no change was observed between normal and activated He under reduced conditions. However, under non-reduced condition of normal He, several minor bands were observed at oligomeric position of He subunit, which disappeared upon activation. These results indicate that a split of the reductive bond, such as the disulfide bond between subunits, is essential for He activation. This is the first report to show the enzymatic conversion of He and the presence of the covalent bond in the He subunit of crustaceans. (C) 2002 Elsevier Science Inc. All rights reserved.