PHOSPHOTRANSACETYLASE OF ESCHERICHIA-COLI-B, ACTIVATION BY PYRUVATE AND INHIBITION BY NADH AND CERTAIN NUCLEOTIDES

1. 1.|Phosphotransacetylase of Escherichia coli B has been found to be an allosteric enzyme which was activated by pyruvate and inhibited mainly by NADH. NAD+ did not affect the enzyme activity. 2. 2.|ADP and ATP also inhibited the enzyme, But their inhibitory strengths were only one-quater and one-tenth of NADH, respectively. All these inhibitors affected the enzyme reaction, noncompetitively with CoA and sigmoidally with respect to the acetyl phosphate concentration. Pyruvate activated the enzyme by lowering Km for acetyl phosphate without a change in vmax. A stimulatory site and an active site were distinct from each other. 3. 3.|Pyruvate repressed the inhibitory action of inhibitor and quite effectively activated the enzyme which had been inhibited by inhibitors, while it did not overcome the sigmoidicity of the reaction, indicating that inhibition and activation were based on separate mechanisms. 4. 4.|These inhibitors and activator were not consumed during the phosphotransacetylase acetylase reaction of E. coli B, in accordance with the result that phosphotransacetylase from Clostridium kluyveri was not affected by these effectors. © 1969.