Hemocyanin a Most Likely Inducer of Black Spots in Kuruma Prawn Penaeus japonicus During Storage

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°C 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.