Studies on Phosphomutases: II. EFFECTS OF 1,3-DIPHOSPHOGLYCERATE ON PHOSPHOGLUCOMUTASE

Abstract

Abstract Low concentrations of 1,3-diphosphoglyceric acid (1,3-di-PGA) stimulated phosphoglucomutase in the reaction without added glucose 1,6-diphosphate. The concentration for half-maximal stimulation was about 5 x 10-6 m. The response to 1,3-di-PGA passed through a maximum value at 1 x 10-5 m. Low concentrations of glucose-1,6-di-P showed stimulatory effects additive with the effects of low concentrations of 1,3-di-PGA. With glucose-1,6-di-P near or above its Km, 1,3-di-PGA above 2 x 10-7 m was inhibitory. The inhibition by 1,3-di-PGA appeared competitive with glucose-1,6-di-P when glucose 1-phosphate was 3.3 mm; the Ki was about 5 x 10-6 m. The stimulatory influence of 1,3-di-PGA has tentatively been attributed to its overcoming of glucose-1-P inhibition and to the likelihood that it phosphorylates dephosphoenzyme. 1,3-Di-PGA generated in situ or added as a purified reactant in the presence of glucose monophosphate and phosphoglucomutase promoted production of glucose-1,6-di-P that did not parallel the over-all mutase reaction. Glucose-1,6-di-P therefore did not accumulate merely as a function of increased mutase turnover, but presumably owing to displacement from the enzyme by 1,3-di-PGA. Hydroxylamine markedly inhibited glucose-1,6-di-P production. Commercial preparations of yeast 3-phosphoglycerate kinase (PGA-kinase) used for generating 1,3-di-PGA in situ contained phosphoglucomutase as a contaminant. After PGA-kinase was freed of phosphoglucomutase by gel filtration, glucose-1,6-di-P production was totally dependent on separately added phosphoglucomutase. 2,3-Diphosphoglyceric acid and 3-phosphoglyceric acid inhibited the mutase reaction competitively with glucose-1,6-di-P. The Ki values were about 5 x 10-5 m and 5 x 10-4 m, respectively.