Substrate inhibition in an enzymatic ordered bireactant system: non-linear modelling of the kinetics of hypoxanthine-guanine-phosphoribosyltransferase |
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| Authors: | Barbara M Praest Helmut Greiling and Rüdiger Kock |
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| Institution: | (1) Institute for Clinical Chemistry and Pathobiochemistry, Medical Faculty, University of Technology Aachen, Pauwelsstrasse 30, D-52057 Aachen, Germany, DE |
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| Abstract: | Hypoxanthine-guanine-phosphoribosyltransferase (HGPRT; EC 2.4.2.8) was determined as an enzyme following an ordered bireaction
in the presence of substrate inhibition due to hypoxanthine. This kind of inhibition has not been postulated for HGPRT so
far. The mechanism and the kinetic constants of the reaction of HGPRT from Saccharomyces cerevisiae were investigated by initial
velocity studies involving a non-linear regression analysis. In addition, two kinds of experimental designs were compared:
the variation of hypoxanthine concentrations over wide ranges at different of fixed levels of 5-phosphoribosyl-1-pyrophosphate,
and the use of five appropriate sets of experimental conditions each characterized by different hypoxanthine and 5-phosphoribosyl-1-pyrophosphate
concentrations. Both experimental designs were consistent with an ordered bi bi mechanism including a dead-end-complex between
the enzyme and hypoxanthine.
Received: 25 April 1997 / Revised: 9 June 1997 / Accepted: 16 June 1997 |
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