This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Enzyme regulated by phosphorylation 
Select and explain. 
A. Glucokinase, B. Glycogen synthetase, C. Pyruvate dehydrogenase, D. Isocitrate
B: Glycogen synthetase
Answer: B: Glycogen synthetase 
Explanation: Glycogen Synthase catalyzes elongation of glycogen chains. Glycogen Synthase catalyzes transfer of the glucose moiety of UDP-glucose to the hydroxyl at C4 of the terminal residue of a glycogen chain to form a (1 4) glycosidic linkage (diagrams p. 633):glycogen (n residues) + UDP-glucose glycogen (n +1 residues) + UDPRef: DM Vasudevan, 6th edition, page no: 106