[Trace elements as activation factors of enzymes: characteristic enzymes and their activation mechanisms]

We here describe activation mechanisms of three characteristic metalloenzymes by metals. The copper-containing amine oxidase contains a topaquinone residue at the active site. The inactive precursor form of the enzyme, which contains a tyrosine residue at the position corresponding to topaquinone of the matured protein, was isolated and converted to the matured form by incubation with cupric ions through self-processing of the protein. The selenocysteine residue of selenium-containing formate dehydrogenase is synthesized cotranslationally through a process directed by a UGA codon that normally functions as a stop codon. We describe the mechanism of recognition of UGA and specific incorporation of selenium into the protein. Vanadium-containing haloperoxidases afford stable apo forms lacking vanadium. Reconstitution of holo forms by vanadium ions are also described.