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Abstract
Phosphoketolase(s), catalysing the cleavage of xylulose 5-phosphate and fructose 6-phosphate, were found in Rhodotorula graminis, R. glutinis, Candida 107 and C. tropicalis. Activity towards the latter substrate only was found in C. humicola. Neither activity was found in Saccharomyces carlsbergensis. The enzyme(s) were isolated and purified eightfold from R. graminis. Inorganic phosphate, thiamin pyrophosphate and Mg2+ were required for activity. The enzyme had a K m of 1·25 mm for xylulose 5-phosphate and was markedly sensitive to NADH, NADPH, ATP and acetyl-CoA and less sensitive to phosphoenol-pyruvate, citrate and dodecanoyl-CoA. The activity of phosphoketolase was halved in the presence of an active transketolase which competes with it for the same substrate. The contribution of phosphoketolase to glucose catabolism may be only slight.
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