Studies on Glycogen Metabolism in Human Leukemic Cells. IL Kinetic Parameters of the Two Forms of Glycogen-Synthetase

Abstract

Two forms of glycogen synthetase from leukemic leucocytes have been obtained in the 100,000 X g glycogen particulate fraction. About 90% of the enzyme was normally found in the D form. I form was produced only after preincubation of the crude extract at 30° C, in the presence of mercaptoethanol and Mg2+.

In spite of the lower glycogen levels and the lower glycogen synthetase activity found in leukemic leucocytes as compared to normal leucocytes, the kinetic studies of the two forms of glycogen synthetase showed that the enzyme seems to have similar characteristics to those reported for the same enzyme in normal leucocytes and in other tissues. The Km values for UDPG were in the range of 10-4 M.

The activation constant for glucose-6-P was found to be lower in magnitude in leukemic leucocytes of the lymphoid series (10-4 M) than in leucocytes of myeloid series (10-3 M).