Which of the following is a key regulatory enzyme in glycogen metabolism?

Glycogen synthase is a pivotal enzyme in glycogen metabolism because it is responsible for the synthesis of glycogen from glucose units. This enzyme catalyzes the addition of glucose residues to the growing glycogen chain, effectively linking them together to form the polysaccharide. The regulation of glycogen synthase is crucial for maintaining glucose homeostasis in the body, as it determines the rate at which glucose can be stored as glycogen in liver and muscle tissues. When energy levels are high, insulin activates glycogen synthase to facilitate the conversion of excess glucose into glycogen for later use, while during times of low glucose availability, glycogen synthase is inhibited to prevent glycogen synthesis.

Other enzymes mentioned have important roles in metabolism, but they are not the main regulatory enzymes for glycogen metabolism. Hexokinase is primarily involved in the phosphorylation of glucose to glucose-6-phosphate, an early step in glucose metabolism. Phosphofructokinase plays a key regulatory role in glycolysis, controlling the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Aldolase is involved in the glycolytic pathway as well, specifically catalyzing the cleavage of fructose-1,