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Insulin Affects Many Enzymes

Insulin affects the activity of many enzymes, most of which are involved in getting rid of glucose. However, fat metabolism is also affected. Glucoki- nase is a liver enzyme that phosphorylates glucose to glucose-6-phosphate (see Biochemical Connections 6.3). It is induced by insulin, so that when insulin is present, glucose in the liver is sent toward catabolic pathways, such as pentose phosphate or glycolysis. Insulin also activates liver glycogen synthase and deactivates glycogen phosphorylase, causing glucose to be put into a polymeric form. In addition, insulin stimulates glycolysis through activation of phosphofructokinase and pyruvate dehydrogenase. Insu- lin also has a large effect on fatty-acid metabolism. It increases fatty-acid synthesis via stimulation of acetyl-CoA carboxylase (ACC), and it increases