Physicochemical and Enzymatic Properties of ATP: Nucleotide Pyrophosphotransferase

The molecular weight determined by the sedimentation equilibrium and SDS Polyacrylamide gel electrophoresis was 29,000 and 28,000, respectively. Isoelectric point of the enzyme was determined as pH 7.7. This enzyme contained large amounts of alanine, aspartic acid, glutamic acid and serine, and no cysteine residue was found. The enzyme was inhibited by SDS, KMnO₄, EDTA and tetracycline. GTP and GDP were the most active as pyrophosphate acceptor to the enzyme. The apparent Km for ATP was 2.2×10^?4 m and that for GTP was 2.1×10^?4m in the reaction of ATP+GTP→AMP+pppGpp. On the other hand, in the reaction of 2ATP→AMP+pppApp, the apparent Km for donor and acceptor ATP was 1.7×10^?3m. Effects of pH and metal ions on the enzymatic synthesis of pppGpp were also studied.