（翻译）Controls over the enzymes of different pathways allow cells to direct the flow of nutrients, building materials, waste products, hormones, and so on in suitable ways. When you eat too much sugar, enzymes in your liver cells act on the excess, converting it first to glucose and then to glycogen or fat. When your body uses up glucose and needs more, enzymes break down glycogen to release its glucose subunits. In this case, a hormone called glucagon(胰高血糖素) acts as a control over enzyme activity. It stimulates the key enzyme in the pathway by which glycogen is degraded, and it inhibits the enzyme that catalyzes glycogen formation.
