Copper metallothionein, a copper-binding protein from Neurospora crassa.

Copper is an essential constituent of many proteins which participate in biologically important reactions. In contrast to iron, where different metal storage and transport proteins have been extensively characterised, the existence of copper proteins serving such functions is still a matter of controversy. Studies on the biosynthesis of tyrosinase from Neurospora crassa with respect to the copper status of this fungus have shown that this organism accumulates copper with the concomitant synthesis of a small molecular weight copper-binding protein. This protein is now shown to have a striking sequence homology to the zinc- and cadmium-containing metallothioneins from vertebrates. Growth experiments suggest that this molecule fulfills several important physiological functions in this organism such as copper storage, copper detoxification and provision of copper for tyrosinase.