Catalytic activity is the augmentation of the rate and energy of a chemical reaction by a substance that is not itself changed in the reaction. In biological systems, it is performed by enzymes that are essential for normal life processes. By lowering the necessary energy required to initiate a reaction, enzymatic pathways increase the rate at which cells perform essential chemical functions. Catalysis is controlled by regulating enzymes. Some of these involve changes to the enzyme structure, while others operate by altering the cellular environment in which catalytic activity takes place.
In general chemistry, catalytic activity or catalysis is any change — increase or decrease — in a reaction's rate by an agent which is not chemically changed by the process. In industry, this can mean any number of agents used to increase the rate and yield of reactions, but in biochemistry, catalytic activity refers to the work of enzymes, the proteins found in all organisms that mediate most cellular functions, including metabolism. Few if any biological processes would occur at a rate sufficient to sustain life without enzymatic catalysis.
Some reactions would not happen at all without the catalytic activity of enzymes. Ordinarily, many molecules have an energy barrier to reacting together. Called activation energy, this limit must be overcome for chemical reactions to proceed.
In some cases, a high activation energy threshold means that the reactants are unlikely to a react on their own, or will do so at a slow rate. When enzymes temporarily bind to one or more reactants, the necessary activation energy is lowered, and the reaction rate accelerates. Enzymes can also inhibit the activation of other enzymes and slow down the process.
Enzymatic activity often results in multiple-step biochemical reactions, which each rely on a different catalyst and are contingent on the product of the previous step. Physically, catalytic activity of many different enzymes occurs in the same cellular organelle, speeding up the reaction rate as a result. Changes in pH and in temperature can, to a point, work in synergy to increase the pace of catalysis. Temperatures beyond a certain range can damage the structure of an enzyme's proteins, rendering it incapable of activity.
In biological systems, catalytic activity is regulated by several different mechanisms. Enzymes usually are made from inactive precursor proteins, and these become active only through the action of another enzyme or an environmental change such as movement from the inside of the cell to the outside. Feedback inhibition reduces catalysis when the product of one or more enzymatic pathways accumulates in the cell, blocking further release or manufacture of the enzyme that catalyzed the initial reaction. Similarly, reduced amounts of the reaction products will increase production of the enzyme.