TYR and skin neoplasm: However, melanin overproduction is related to dermatologicalconditions like melasma, ephelides, sunspots, pigmented acne scars,and even skin cancer. The rate-limitingstep of the biosynthesis of melanin is represented by the hydroxylationand oxidation of l-tyrosine to dopaquinone, catalyzed bythe enzyme tyrosinase (TYR).