Tyrosinase exhibits catalytic activity for the ortho-hydroxylation of monophenols to diphenols as well as their subsequent oxidation to
quinones. Owing to polymerization of these quinones, brown-coloured high-molecular-weight
compounds called melanins are generated. The latent precursor form of polyphenol oxidase
4, one of the six tyrosinase isoforms from Agaricus bisporus, was purified to homogeneity and crystallized. The obtained crystals belonged to
space group C121 (two molecules per asymmetric unit) and diffracted to 2.78 Å resolution. The protein
only formed crystals under low-salt conditions using the 6-tungstotellurate(VI) salt
Na6[TeW6O24]·22H2O as a co-crystallization agent.