Presence of hemocyanin with diphenoloxidase activity in deepwater pink shrimp (Parapenaeus longirostris) post mortem

Polyphenoloxidase and hemocyanin are two proteins which although very similar perform different physiological functions in crustaceans. This paper reports the presence of hemocyanin with diphenoloxidase activity in deepwater pink shrimp (Parapenaeus longirostris) post mortem. Polyacrylamide gels and specific inhibitors and substrates of mono- and diphenoloxidases were used for purposes of recognition, and MALDI-TOF mass spectrometry for identification. Presumptive polyphenoloxidase was found in an inactive form in cephalothorax following capture, subsequently becoming active during storage. Also in the course of storage, hemocyanin acquired the ability to oxidize diphenols. Ascorbic acid, sodium metabisulphite and tropolone inhibited the prooxidant activity of both presumptive polyphenoloxidase and hemocyanin in the gels. 4-Hexylresorcinol did not avoid the appearance of activity bands in the gel corresponding with hemocyanin, maybe because 4-hexylresorcinol is described as slow-binding inhibitor. The acquired prooxidant activity of hemocyanin following capture is especially important because of the rapid development of melanosis in deepwater pink shrimp during storage.