A MODEL FOR ROLE OF METAL IONS IN ENZYME-CATALYZED HYDROLYSIS OF POLYPHOSPHATES

Several new compounds containing pyrophosphate linkages and other oxygen and nitrogen ligands have been synthesized and purified. It was thought that the presence of these other ligand groups might induce metal ions to bind to the penultimate monoanionic phosphate position while leaving the terminal dianionic phosphate position unbound. This mode of binding would result in a metal ion-ligand complex resembling an unsymmetrical diester of pyrophosphoric acid. As previous work had indicated that such diesters hydrolyze extremely rapidly, it was hoped that the rates of pyrophosphate hydrolysis of the newly synthesized compounds would be greatly accelerated by metal ions, thus providing an attractive model for the binding of metal ions to substrates on ihe surface of polyphosphatases. The effects of a large number of metal ions on the hydrolysis rates of these compounds were studied and in no case was significantly large catalysis found, even though 31P nuclear magnetic resonance studies revealed that the desired mode of binding could be at least partially obtained. These findings were taken as strong evidence against the validity of the proposed model. © 1969, American Chemical Society. All rights reserved.