All About Enzymes!

Enzymes are molecules that catalyze, or increase, the rates of chemical reactions by lowering the activation energy of the reaction. Enzymes are usually large molecules with 1 site for a substrate (reactant) to attach. This is known as the active site. When a substrate is attached, the two together are known as the enzyme-substrate complex. The products are released after the reaction occurs.

Modulators attach at the binding site of enzymes and affect the catalytic rate of the enzymes. Stimulators increase the rate while inhibitors decrease it. ATP, for example, is an inhibitor, while ADP and Pi are stimulators.

Alloterism describes the effect of modulators, since they can change the shape of parts on the enzyme. A multivalent enzyme is one which can be affected by several modulators.

Maximum velocity (Vmax) is a descriptive parameter of enzynmes. The Michaelis-Menten constant (Km) describes the interaction between a substrate and an enzyme. It occurs when the concentration of the substrate is 1/2 Vmax.

At rest, normally high levels of ATP and CP inhibit energy metabolism. When exercise starts, ATP breaks down and the existence of ADP and Pi stimulate energy metabolism.