Question

1. Describe the function of the following enzymes: glycogen phosphorylase, glycogen synthase, protein kinase a, adenylate kinase, branching enzyme

Answer 1

Glycogen phosphorylase : Glycogen phosphorylase is a phosphorylase enzyme it catalyses the rate-limiting step in glycogenolysis in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond.

Glycogen Synthase : It is one of the key enzyme involved in the conversion of glucose into glycogen (glycogenesis). In other words it combines with excess glucose residues to form a polymeric chain and gets stored as glycogen.

Protein Kinase a : Protein Kinase a (PKA)also known as cAMP dependent protein kinase. It is a family of enzymes whose activity is dependent on cellular levels of cAMP (Cyclic AMP). It has several functions in the cell, including regulation of glycogen, sugar, and lipid metabolism.

Adenylate kinase : It is also known as ADK or myokinase . It is a phosphotransferase enzyme that catalyzes the interconversion of adenine nucleotides (ATP, ADP, and AMP). It plays an important role in cellular energy homeostasis by constantly monitoring phosphate nucleotide levels inside the cell.

Branching Enzyme : Glycogen branching enzyme is an enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen.During glycogen synthesis, a glucose 1-phosphate molecule reacts with uridine triphosphate to become uridine diphosphate-glucose, an activated form of glucose. The activated glucosyl unit of UDP-glucose is then transferred to the hydroxyl group at the C-4 of a terminal residue of glycogen to form an α-1,4-glycosidic linkage. The extended glycogen polymer is branched by glycogen branching enzyme to provide glycogen breakdown enzymes, such as glycogen phosphorylase, with a large number of terminal residues for rapid degradation.