64] Muscle and liver UDP-glucose: α-1,4-glucan α-4-glucosyltransferase (glycogen synthetase)

Abstract

Publisher Summary This chapter discusses the synthesis of α-1,4-glucan α-4-glucosyltransferase. It is possible to demonstrate in muscle and in liver, two different forms of the enzyme—one dependent for activity on the presence of glucose 6-phosphate in the test, the other showing activity in the absence of the cofactor. The synthetase activity is measured by the amount of radioactivity incorporated into glycogen from uridine diphosphate (UDP)-glucose- 14 C in the presence of nonradioactive glycogen primer, glucose 6-phosphate being absent when the I activity is determined and being added if the total activity, I + D, is to be measured. Glycogen synthetase is purified from dog, rat, lamb, and rabbit muscle by several different methods. The two procedures used with rabbit, dog, and rat muscle to prepare the enzyme and to obtain preparations enriched in D and I forms are discussed in the chapter. In the presence of glucose 6-phosphate, the enzyme shows maximal activity at pH 8.3; when glucose 6-phosphate is absent, the pH optimum seems to be about 7.