The mechanism of activation of phosphoglucomutase by chelating agents

Abstract

An 8-hydroxyquinoline test for metals has been used to show the presence of metals in the highly purified preparations of phosphoglucomutase, and to follow the preparation of a "metal-free" enzyme. The "metal-free" enzyme shows a positive test for metals after dialysis against glass-distilled water. The necessity of a chelating agent in the assay of phosphoglucomutase is shown to be due to removal of inhibitory-metal impurities in the system. Considerable activity is obtained even in the absence of chelating agents if special precautions are taken to keep the system "metal-free". The extent of the activation by metal-chelating agents varies with the amount of the metal impurities present. It is concluded that the activation does not involve a complex of phosphoglucomutase and chelating agent. If phosphoglucomutase is incubated with ethylenediaminetetra-acetic acid before the assay, a further activation of a different kind is obtained. This is time-dependent, reversible, not obtained with other chelating agents under the same conditions and does not affect the Michaelis constant for Mg2+ ion. If preincubation is made in the presence of magnesium, the further activation is also obtained with 8-hydroxyquinoline.