Mammalian tyrosinase. Structural and functional interraltionship of isozymes

The isozymes of tyrosinase from normal and malignant melanocytes were studied; the data indicates that each consists of a basic tyrosinase polypeptide, and differs by post-translational modifications. T3 represents the de novo form of the enzyme; it is converted to T1 in vivo by the addition of sialic acids and neutral sugars, and in turn, to T4 by complexing with mealanosomal membrane constituents. The T2 isomer is suggested to be an artefact of the electrophoretic procedure, and due to deamidation of T3. It is shown that the apparent kinetics of enzyme activity are unafffected by any of these modifications.