MONOPHENOL OXIDASE ACTIVITY FROM THE CUTICLE OF FLORIDA SPINY LOBSTER (PANULIRUS-ARGUS)

Endogenously activated phenoloxidase (PO) from the cuticle of Florida spiny lobster was purified 37-fold. It had an isoelectric point of 4.76 and an apparent molecular weight of 81 200 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Ion-pair reversed-phase high-performance liquid chromatography demonstrated that PO can catalyze the hydroxylation of L-tyrosine to dihydroxyphenylalanine (mono-PO activity). The optimum pH for hydroxylation was between 6.0 and 6.5, and the PO was most stable from pH 6 to 8. The optimum temperature for reaction was 40 degrees C, and PO was stable up to 40 degrees C. The apparent Michaelis-Menten constant (K-m) was 0.97 mM for PO hydroxylation of L-tyrosine.