Biosynthesis of selenophosphate

Article type: Research Article

Authors: Lacourciere, Gerard M.

Affiliations: Laboratory of Biochemistry, National Heart, Lung, Blood Institute National Institutes of Health, Building 3, Room 103, Bethesda, MD 20892, USA Tel.: +1 301 496 3002; Fax: +1 301 496 0599

Abstract: Selenophosphate synthetase, the product of the selD gene, produces the highly active selenium donor, monoselenophosphate, from selenide and ATP. Positional isotope exchange experiments have shown hydrolysis of ATP occurs by way of a phosphoryl‐enzyme intermediate. Although, mutagenesis studies have demonstrated Cys^{17} in the Escherichia coli enzyme is essential for catalytic activity the nucleophile in catalysis has not been identified. Recently, selenophosphate synthetase enzymes have been identified from other organisms. The human enzyme which contains a threonine residue corresponding to Cys^{17} in the E. coli enzyme, has been overexpressed in E. coli. The purified enzyme shows no detectable activity in the in vitro selenophosphate synthetase assay. In contrast, when the human enzyme is expressed to complement a selD mutation in E. coli, in the presence of ^{75}Se, incorporation of ^{75}Se into bacterial selenoproteins is observed. The inactive purified human enzyme together with the very low determined specific activity of the E. coli enzyme (83 nmol/min/mg) suggest an essential component for the formation of selenophosphate has not been identified.

Journal: Biofactors, vol. 10, no. 2-3, pp. 237-244, 1999