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Selenophosphate synthetase : enzyme properties and catalytic reaction
Journal article   Open access   Peer reviewed

Selenophosphate synthetase : enzyme properties and catalytic reaction

Z Veres, ICK YOUNG Kim, T. D Scholz and T. C Stadtman
The Journal of biological chemistry, Vol.269(14), pp.10597-10603
1994
DOI: 10.1016/S0021-9258(17)34101-7
PMID: 8144648
url
https://doi.org/10.1016/s0021-9258(17)34101-7View
Published (Version of record) Open Access

Abstract

Selenophosphate synthetase, the product of the selD gene, produces the biologically active selenium donor compound, monoselenophosphate, from ATP and selenide. Isolation of the enzyme and characterization of some of its physical and catalytic properties are described. Magnesium ion and a monovalent cation, K+, NH4+, or Rb+, are required for catalytic activity. Polyphosphates and other common nucleotide triphosphates do not replace ATP as substrate. The stoichiometry of the catalytic reaction (Reaction 1) was established using 31P NMR, anaerobic molecular sieve chromatography, and radiochemical labeling procedures. ATP+selenide+H2O–>selenophosphate+Pi+AMP. In the absence of selenide, ATP is converted completely to AMP and orthophosphate upon prolonged incubation with elevated levels of enzyme. AMP is a competitive inhibitor of ATP, Ki = 170 microM, whereas selenophosphate and orthophosphate are weak inhibitors indicating a multistep reaction. Attempts to obtain direct evidence for a postulated enzyme-pyrophosphate intermediate using several experimental approaches are described. No exchange of [14C]AMP with ATP could be detected after the enzyme was freed of traces of contaminating adenylate kinase by chromatography on phenyl-Sepharose.
 Analytical, structural and metabolic biochemistry Biological and medical sciences Enzymes and enzyme inhibitors Fundamental and applied biological sciences. Psychology Transferases

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