Specific inhibition by antityrosinase antibodies of tyrosinase-mediated melanogenesis.

Polyclonal antibodies to hamster melanoma tyrosinase were raised in rabbits, and series of immunoinhibition experiments with a purified enzyme and specific immunoglobulins were carried out. Tyrosinase activity was determined by a set of radiochemical and spectrophotometric methods utilizing tyrosine, dopa, dopamine, or dihydroxyindole (DHI) as substrates. The quantitative data obtained indicated that the complexing of tyrosinase with its specific antibody inhibited melanogenesis in a specific manner: dopachrome formation from dopa and dopamine conversion to melanin were not affected and all other enzyme activities comprising the DHI oxidation step were inhibited to various degrees. Additionally, tyrosine hydroxylation was also slightly inhibited. The data obtained implied that melanogenesis was restricted at the point of DHI oxidation. From observations on the immunoinhibition of a DHI oxidation at varying dopa-cofactor concentrations, we propose that dopa-cofactor may be bound at separate site than DHI and thus may act as a positive allosteric effector for DHI oxidation by tyrosinase. Study of tyrosinase immunoinhibition by the antibodies against the enzyme thus seems to provide a valuable system for investigating the tyrosinase-mediated melanogenesis.