Studies on crystalline yeast phosphoglucomutase: The presence of intrinsic zinc

Abstract

Yeast phosphoglucomutase (α- d-glucose-1,6-diphosphate:α- d-glucose-1-phosphate phosphotransferase, EC 2.7.5.1) was inhibited by EDTA and was active without any addition of a bivalent cation. After the enzyme was dialyzed against the EDTA solution, the enzyme activity was recovered by removal of EDTA by passage through a Sephadex column. These observations suggested that the yeast enzyme contained an intrinsic metal ion essential for catalytic activity and that the EDTA inhibition was due to the formation of the enzyme-metal-EDTA ternary complex. The enzyme activity was protected from EDTA inhibition in the presence of the coenzyme. About 1 mole of zinc per mole of the enzyme was observed by atomic absorption measurements. These observations suggested that the intrinsic zinc might exist on the coenzyme binding site. The existence of intrinsic zinc in yeast phosphoglucomutase is in contrast to the muscle enzyme which requires extrinsic Mg 2+ for activity. The yeast enzyme catalyzes the reaction by a different pathway from the muscle enzyme. The role of bivalent cations in the phosphoglucomutase reaction mechanism is discussed.