Selenophosphate synthetase: enzyme labeling studies with [gamma-32P]ATP, [beta-32P]ATP, [8-14C]ATP, and [75Se]selenide.
Selenophosphate synthetase catalyzes a reaction in which ATP and selenide are converted to H3SeP03, H3P04, and AMP in a 1:1:1 ratio. Selenophosphate is derived from the gamma phosphoryl group and orthophosphate from the beta phosphoryl group of ATP. In the absence of selenide, a slow reaction in which ATP is converted quantitatively to 2 H3P04 and AMP occurs. Labeling experiments carried out to detect a putative enzyme-bound pyrophosphate intermediate in the overall reaction showed that up to 0.6 equivalent of the 32P label from [gamma-32P]ATP was bound to protein under enzyme turnover conditions, but only a negligible amount of 32P from [beta-32P]ATP was present. Thus, no Enz-PP intermediate was present in a detectable amount under the experimental conditions used. Isolated enzyme samples contained 75Se from 75Se-labeled selenide and [14C]AMP from [8-14C]ATP in amounts similar to the bound 32P from [gamma-32P]ATP, suggesting that two of the final products, selenophosphate and AMP, were the radioactive compounds detected in these experiments.
Liu
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Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Stadtman
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D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002250:Carbon Radioisotopes / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry; D029721:Drosophila Proteins; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D007553:Isotope Labeling / Q000379:methods*; D007554:Isotopes; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010761:Phosphorus Radioisotopes / Q000378:metabolism; D010770:Phosphotransferases; D012643:Selenium / Q000378:metabolism*; D013440:Sulfides / Q000378:metabolism; D013691:Tellurium / Q000378:metabolism
D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D029721:Drosophila Proteins; D004798:Enzymes; D007554:Isotopes; D010761:Phosphorus Radioisotopes; D013440:Sulfides; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; C062762:selenophosphate synthetase; D012643:Selenium; D003545:Cysteine; D013691:Tellurium