Inhibitory sites in enzymes: Zinc removal and reactivation by thionein
AUTOR(ES)
Maret, Wolfgang
FONTE
The National Academy of Sciences
RESUMO
Thionein (T) has not been isolated previously from biological material. However, it is generated transiently in situ by removal of zinc from metallothionein under oxidoreductive conditions, particularly in the presence of selenium compounds. T very rapidly activates a group of enzymes in which zinc is bound at an inhibitory site. The reaction is selective, as is apparent from the fact that T does not remove zinc from the catalytic sites of zinc metalloenzymes. T instantaneously reverses the zinc inhibition with a stoichiometry commensurate with its known capacity to bind seven zinc atoms in the form of clusters in metallothionein. The zinc inhibition is much more pronounced than was previously reported, with dissociation constants in the low nanomolar range. Thus, T is an effective, endogenous chelating agent, suggesting the existence of a hitherto unknown and unrecognized biological regulatory system. T removes the metal from an inhibitory zinc-specific enzymatic site with a resultant marked increase of activity. The potential significance of this system is supported by the demonstration of its operations in enzymes involved in glycolysis and signal transduction.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=26715Documentos Relacionados
- Hybrid restriction enzymes: zinc finger fusions to Fok I cleavage domain.
- Control of zinc transfer between thionein, metallothionein, and zinc proteins
- Imidazoline binding sites on receptors and enzymes: Emerging targets for novel antidepressant drugs?
- Shared active sites in oligomeric enzymes: model studies with defective mutants of aspartate transcarbamoylase produced by site-directed mutagenesis.
- Selenium redox biochemistry of zinc–sulfur coordination sites in proteins and enzymes