Nitrogen Ligands at the Active Site of Alkaline Phosphatase
AUTOR(ES)
Taylor, June S.
RESUMO
The two Zn(II) ions of native Escherichia coli alkaline phosphatase (EC 3.1.3.1) that are necessary for activity have been replaced by 63Cu(II). Titration of apoenzyme with up to 2 eq of Cu(II) gives a homogeneous species with an electron spin resonance typical for Cu(II) in an axially symmetric environment, with Az = 496 MHz, gz = gǁ = 2.27, and gx = gy = 2.05. At least seven nitrogen hyperfine lines, spaced 11 G apart, are clearly resolved on the M = +[unk] Cu(II) hyperfine peak in the parallel region. When more than 2 eq of Cu(II) are added, the electron spin resonance spectrum shows at least two types of Cu(II) binding sites; the additional site, or sites, are characterized by lower g and higher Az values. When Cu(II) is added to native Zn(II) alkaline phosphatase or to apoenzyme incubated with 2 eq of Zn(II), the electron spin resonance spectrum shows little or no trace of the species with higher g values and nitrogen splitting. These results indicate that the species with higher g represents copper bound at the site normally occupied by the 2 Zn (II) ions necessary for enzyme activity, and that the metal ion at this site has at least 3 equivalent nitrogen ligands, probably histidyl side chains.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=426581Documentos Relacionados
- Studies on the active center of alkaline phosphatase of E. coli.
- Binding of ligands to the active site of carboxypeptidase A.
- Selectivity of the cleavage/attachment site of phosphatidylinositol-glycan-anchored membrane proteins determined by site-specific mutagenesis at Asp-484 of placental alkaline phosphatase.
- Evidence for a spin-coupled binuclear iron unit at the active site of the purple acid phosphatase from beef spleen.
- THE PHOSPHORYLATION OF ALKALINE PHOSPHATASE*