Abstract
A protyrosinase has been isolated from fifth instar larval haemolymph of the tobacco hornworm, Manduca sexta (L.) by ammonium sulphate fractionation, hydroxylapatite chromatography and gel filtration. It exhibited a single band after polyacrylamide gel electrophoresis at pH 8.5 and two bands in the presence of sodium dodecyl sulphate with apparent molecular weights of 7.7 × 10 4 and 7.1 × 10 4 . The proenzyme is a metalloprotein containing 0.18% copper. The activating enzyme was partially purified from pharate pupal cuticle by ammonium sulphate precipitation and hydroxylapatite chromatography. The activation was inhibited by di isopropylphosphorofluoridate and had a pH optimum of 8.8. Chymotrypsin also activated the proenzyme. The cuticular activator is probably a serine protease. Activated protyrosinase exhibited physical, chemical and kinetic properties very similar to those of tyrosinase extracted from pharate pupal cuticle. Haemolymph protyrosinase may serve as a precursor for both haemolymph and cuticular tyrosinases that synthesize catecholamines and quinones used for wound healing, parasite encapsulation as well as for cuticular stabilization and pigmentation.
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