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We investigated the enzymatic properties and immunohistochemical localization of cuticular hemocyanin, a known oxygen transporter in the prawn Penaeus japonicus. The molecular weight of hemocyanin purified from the cuticle was estimated to be 67-77 k using SDS-PAGE, and the purified protein was effectively converted into a phenoloxidase-like enzyme by an SDS-treatment. The activated enzyme catalyzed the o-hydroxylation of monophenols and the oxidation of o-diphenols and was inhibited by typical inhibitors of phenoloxidase. These characteristics were nearly identical to the enzymatic properties of hemolymph hemocyanin. Immunological detection showed a diffuse distribution of hemocyanin over the exocuticle and endocuticle, and a higher signal level was observed in the latter. Based on these results, roles of hemocyanin in various physiological processes such as immune response and sclerotization of the cuticle were discussed.

Hemocyanin (Hc) from plasma of kuruma prawn was characterized as a potent inducer of black spots during storage. An oxygen transporter, hemocyanin was converted into phenoloxidase (PO)-like enzyme (HdPO) with SDS treatment as well as prophenoloxidase isolated from hemocytes. Both enzymes showed similar biochemical properties. The isolated PO, however, was so unstable that its activity was drastically reduced when frozen and thawed at -25 ЊC for less than a week, while HdPO completely retained its activity for more than a month, suggesting that HdPO is a key factor in black spot development in freeze-thawed prawn.

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