Glycogen synthase can use glucose as an acceptor

Area of Science:

• Biochemistry
• Enzymology
• Carbohydrate Metabolism

Background:

• Glycogen synthase is a key enzyme in glycogen synthesis.
• Purified glycogen synthase requires an acceptor for activity.
• The enzyme's substrate specificity and product formation are not fully elucidated.

Purpose of the Study:

• To characterize the reaction catalyzed by purified rabbit skeletal muscle glycogen synthase.
• To identify the product formed when glucose is used as a substrate.
• To determine the linkage of the glucose disaccharide product.

Main Methods:

• Enzyme purification to homogeneity.
• Enzymatic assays using UDP-glucose and glucose as substrates.
• Radiolabeling studies with UDP-[14C]glucose and [14C]glucose.
• Product identification using co-chromatography and linkage analysis.

Main Results:

• Purified glycogen synthase showed no activity without an added acceptor.
• The enzyme converted glucose to a glucose disaccharide using UDP-glucose.
• The disaccharide product co-chromatographed with maltose and possessed an alpha-1,4 linkage.
• Radiolabeling studies confirmed the asymmetric labeling of the disaccharide.

Conclusions:

• Rabbit skeletal muscle glycogen synthase can synthesize maltose from glucose and UDP-glucose.
• The enzyme requires an acceptor molecule for its activity.
• The product is an alpha-1,4 linked glucose disaccharide, identified as maltose.