Tyrosinase (EC 1.14.18.1) is a copper-containing enzyme that catalyzes several 
reactions in the biosynthesis of melanin pigments and is deficient in patients 
with type I oculocutaneous albinism (OCA1). Tyrosinase is thought to bind two 
copper ions, one at each of two conserved sequence motifs, termed CuA and CuB, 
but to date this has been directly proved only for the Neurospora and mushroom 
enzyme. Here, we demonstrate that mammalian tyrosinase directly binds copper, 
and that the CuA and CuB sites are both required for copper binding and for 
catalytic activity. We show that in human tyrosinase, copper binding by the CuB 
site is most likely coordinated by residues His363, His367, and His389, and that 
copper binding may be cooperative, with copper binding at one site facilitating 
copper binding by the other site. Furthermore, correct folding of the tyrosinase 
polypeptide appears to be necessary for copper binding, and a number of human 
OCA1 mutations disrupt copper binding and thus catalytic function of tyrosinase.