On the mechanism of activation of phosphoglucomutase by metal ions

Publisher Website
Google Scholar
Abstract
Mg is an essential activator of phosphoglucomutase. However, in some cases some activity is found in its absence, which can be suppressed by ethylenediaminetetra-acetic acid and is probably due to residual traces of metals. The apparent Michaelis constant for Mg is about 50 [mu]M, with a concentration of glucose 1-phosphate of either 5 or 0.5 mM. Mg forms complexes with both glucose 1-phosphate and glucose 6-phosphate, with dissociation constants slightly higher than 10 mM, and with the enzyme with a dissociation constant of about 0.5 mM. Phosphoglucomutase is inhibited by l-fluoro-2,4-dinitrobenzene, and Mg protects against this inhibition at concentrations of the order required for full activation. The 1-fluoro-2,4-dinitrobenzene-inhibited enzyme has the same Michaelis constant for Mg as the uninhibited enzyme. From hydrolysates of fully inactive dinitrophenylphosphoglucomutase, 6 molecules of dinitrophenyllysine and about 5 of dinitrophenyltyrosine per molecule of enzyme can be detected. All histidine residues have also reacted with the l-fluoro-2,4-dinitro-benzene. The activation by a "second metal" in addition to Mg2+ ion is also found with pure phosphoglucomutase. It is suggested that its mechanism is similar to the activation by chelating agents.