Multiple forms of tyrosinase in rodents and lagomorphs with special reference to their genetic control in mice

Polyacrylamide gel electropherograms of extracts of pigmented hair bulbs from rodents and lagomorphs indicate that tyrosinase exists in multiple molecular forms. Allelic substitutions at the a, b, c, d, and p color loci in mice reveal that the multiple forms of tyrosinase are subject to complex genetic influences. Depending upon genic constitution, a maximum of three electrophoretically‐separable forms of tyrosinase (T1 = 80,000 m. w.; T2 = 62,000 m. w.; T3 = 66,000 m. w.) can be visualized by incubation of the polyacrylamide gels in L‐DOPA. In certain genotypes of mice, T1, T2, and T3 are either greatly reduced in activity or absent. Urea, SDS, and EDTA fail to dissociate tyrosinase suggesting that the multiple molecular forms of tyrosinase are not simple aggregates of monomeric subunits stabilized by non‐covalent bonds. Tyrosinase corresponding in mobility to the T1 of mice is also found in hair bulb extracts from black rats, black rabbits, gerbils and golden Syrian hamsters. The T2 and T3 components are distinct in the black rat but are represented by a single “T2‐T3” band in the gerbil, hamster and rabbit. An additional T0 band is found in the black rat. Available evidence suggests that T1 of comparable electrophoretic mobility is widely distributed in mammals and may be an additional indication of an underlying broad homology of pigmentary genes. At present, it is not certain whether the multiple forms of tyrosinase are “true” isozymes or a single enzymic moiety bound to structural components of the melanosomal matrix.