20. Phosphoenolpyruvate Synthetase and Pyruvate, Phosphate Dikinase

Abstract

Publisher Summary This chapter discusses the molecular and catalytic properties of phosphoenolpyruvate (P-enolpyruvate) synthetase and pyruvate, phosphate dikinase. Experiments with mutants devoid of P-enolpyruvate synthetase activity have shown the enzyme to be essential for gluconeogenesis in E. coli and Salmonella typhimurium during growth on pyruvate, lactate, alanine, or serine. In addition, they showed that in certain circumstances P-enolpyruvate synthetase may also provide P-enolpyruvate under glycolytic conditions; for instance, in the absence of 6-phospho- fructokinase (16) or triosephosphate isomerase, the normal glycolytic yield of P-enolpyruvate during the catabolism of glucose is halved, and in these circumstances P-enolpyruvate synthetase produces some of the P-enolpyruvate necessary for growth. In contrast to the P-enolpyruvate synthetase reaction, the energetics of the pyruvate, phosphate dikinase reaction, favor the formation of pyruvate from P-enolpyruvate rather than P-enolpyruvate synthesis. Because pyruvate kinase has not been detected in Entarnoeba histolyticu and in Bacteroides symbiosus, it has been suggested that the pyruvate, phosphate dikinase of these organisms in fact plays a glycolytic role. In certain green plants pyruvate, phosphate dikinase provides the P-enolpyruvate for the trapping of carbon dioxide prior to the operation of the Calvin cycle.