Isolation of tyrosinase from bovine eyes

Pigmented tissues from bovine eye were used as a source for isolation of tyrosinase from normal melanocytes. Tyrosinase is highly hydrophobic and the isolation procedure is mainly based on the use of hydrophobic interaction chromatography. The bovine enzyme is, in contrast to the human melanoma tyrosinase, mainly soluble. The predominant part of the ocular enzyme from cow has a molecular weight and isoelectric behavior similar to that of the soluble tyrosinase in the human melanoma cells. The N-terminal amino acid sequence of isolated bovine tyrosinase was determined by automated Edman degradation. The N-terminal amino acid sequence from normal bovine tyrosinase was identical to the sequence of an N-terminal region of mouse melanoma tyrosinase predicted from a c-DNA clone by Kwon et al. (1988). The amino acid sequence of bovine tyrosinase shows homology to that of human tyrosinase (Wittbjer et al., 1989), but three amino acids of the 16 residues determined by us differed. Histidine was the N-terminal amino acid.