Inhibition of phosphoglucomutase by trace metals

Abstract

A quantitative study of the inhibition of phosphoglucomutase provides additional evidence that the necessity for a chelating agent is due to the presence of minute traces of inhibitory metals. Zinc is an inhibitor of phosphoglucomutase, competing with Mg2+ ions, with dissociation constant Kzn 3.9 x 10"14 m. Copper also competes with Mg2+ ions, but the inhibition is not purely competitive. The inhibition by Cu2+ ions can be explained by competition with the Mg2+ ions (Kcu 2.3 x 10-17 M], together with non-competitive combination at a second site (K[image]Cu 2.5 x 10-16 M). Three to four SH groups are present in phosphoglucomutase. Although some inhibition is observed with high concentrations of several SH reagents, phosphoglucomutase does not appear to be an enzyme requiring these groups for activity. The effects are discussed in the light of the amino acid sequence in the active center previously determined.