Allosteric control of Zymomonas mobilis glucose-6-phosphate dehydrogenase by phosphoenolpyruvate.
The second enzyme of the Entner-Doudoroff glycolytic pathway in Zymomonas mobilis, glucose-6-phosphate dehydrogenase, has been found to be inhibited by phosphoenolpyruvate (PEP). In the presence of PEP levels in the micromolar range, the response of the enzyme to glucose 6-phosphate concentration becomes sigmoidal, with a Hill coefficient up to 2. At low ionic strength in the absence of PEP, the response to glucose 6-phosphate concentration is Michaelis-Menten, but at physiological ionic strength and pH, a Hill coefficient of 1.3 to 1.4 was found even in the absence of PEP. Km values for NAD+ and NADP+ are also ionic-strength-dependent, increasing rapidly as salt concentration increases. Some sigmoidicity was also observed for NAD+ in the presence of PEP at low glucose 6-phosphate concentrations. The results can be interpreted in a Monod-Wyman-Changeux model, in which glucose 6-phosphate binds principally to the R-state, PEP to the T-state, and NAD+ to both states. These observations are clearly physiologically significant, and provide an explanation for the control of the balance between glycolytic throughput and ATP consumption in Z. mobilis.
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School of Biochemistry, La Trobe University, Bundoora, Melbourne, VIC 3083, Australia.
D000494:Allosteric Regulation; D005954:Glucosephosphate Dehydrogenase / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D010728:Phosphoenolpyruvate / Q000494:pharmacology*; D017355:Zymomonas / Q000201:enzymology*
D010728:Phosphoenolpyruvate; D005954:Glucosephosphate Dehydrogenase