Methylglyoxal Formation during Glucose Catabolism by Pseudomonas saccharophila

Methylglyoxal synthase, which forms methylglyoxal from dihydroxyacetone phosphate, has been detected in both glucose‐ and succinate‐grown Pseudomonas saccharophila but there was no evidence for methylglyoxal production from d ‐glyceraldehyde. The enzyme was purified 100‐fold from glucose‐grown cells and found to be very similar to Escherichia coli methylglyoxal synthase. It has a pH optimum of 8.2, a molecular weight of approximately 67000 and a K m for dihydroxyacetone phosphate of 0.09 mM. Inorganic pyrophosphate, 3‐phosphoglycerate, phosphoenol‐pyruvate and inorganic orthophosphate were all potent inhibitors, the first three compounds being competitive with respect to dihydroxyacetone phosphate with K 1 values of 0.048 mM, 0.029 mM and 0.096 mM, respectively. Inorganic orthophosphate inhibition appeared to be more complex and was overcome in a co‐operative manner by increasing dihydroxyacetone phosphate concentration. Hill plots suggested that in the presence of inorganic orthophosphate there were three dihydroxyacetone phosphate‐binding sites on the enzyme.