Hemocyanin-derived phenoloxidase activity: A contributing factor to hyperpigmentation in Nephrops norvegicus

The phenomenon of hyperpigmentation (melanosis) in shellfish has long been attributed to phenoloxidase enzymes. Over the last number of years, the oxygen carrier hemocyanin, has demonstrated several immune- and physiological functionalities, most notably, inducible phenoloxidase activity. In this study, hemocyanin purified from the hemolymph of Nephrops norvegicus displays diphenoloxidase activity in the presence of a number of elicitors and retains structural and functional integrity throughout the process of freeze–thawing (at −25 °C). Conversely, cellular phenoloxidase activity (present in cell-lysates), demonstrates >98% reduction in activity after freeze–thawing. We present evidence that hemocyanin may act as a causative agent of hyperpigmentation in N. norvegicus. The inhibition of hemocyanin-derived phenoloxidase activity is discussed, and for the first time, the biophysical interactions of shellfish hemocyanin with known phenoloxidase inhibitors are presented.

► Freeze–thawing results in a drastic decrease in cellular PO activity.
► Hc-derived PO activity is retained after freeze–thawing.
► Hc-derived PO activity can be inhibited by known PO inhibitors.
► The nature of Hc-inhibitor interactions are discussed.
► Hc-derived PO activity contributes to hyperpigmentation in shellfish.