Phenoloxidases from larval cuticle of the sheep blowfly, Lucilia cuprina: Characterization, developmental changes, and inhibition by antiphenoloxidase antibodies

A tyrosinase, enzyme A (EC 1.10.3.1, o ‐diphenol: O 2 oxidoreductase), and a laccase, enzyme B (EC 1.10.3.2, p ‐diphenol: O 2 oxidoreductase), have been partially purified and characterized from larval cuticle of the sheep blowfly, Lucilia cuprina . Enzyme A is active toward a range of o ‐diphenols but not p ‐diphenols, is strongly inhibited by thiourea and phenylthiourea, has a pH optimum between 6.5 and 7.0, and yields a single, 60,000 molecular weight subunit following SDS gel electrophoresis. Enzyme B is active toward both o ‐diphenols and p ‐diphenols, is only slightly inhibited by phenylthiourea, has a pH optimum near 4.5, is highly thermostable, and has an apparent molecular weight of 90,000. Enzyme A appears to be activated from an inactive proenzyme in the cuticle and to be present throughout the wandering phase of the final larval instar, declining at pupariation. Enzyme B is present in active form, increases greatly in the cuticle just at the time of pupariation, and then decreases as sclerotization occurs. Antibodies against enzyme A have been raised in sheep and rabbits, and against enzyme B in rabbits, but diets containing antiphenoloxidase antibodies did not affect development or mortality of fly larvae.