Activation

Activation, the transition of something from an inactive state to an active state—a term especially frequently used in relation to enzymes that pass under special conditions from zymogen or proenzyme into ready enzyme. Thus, prothrombin, under the influence of thrombokinase, passes into thrombin, which participates in blood clotting; the secretin that stimulates the secretion of the pancreas is contained in the mucous membrane of the duodenum and small intestine, and is thought to be in the form of inactive prosecretin, which under the influence of acid passes into secretin. In the doctrine of immunity, one often speaks of the activation of an inactive, due to loss of complement, cytolytic serum (for example, hemolytic) by fresh complement. The activation of the protoplasm of cells is also generally used to explain the fact of stimulation of many functions of the body during protein therapy. Finally, one also speaks of the activation of latent, or generally inactive, infectious foci under the influence of some irritant (for example, tuberculous foci depending on the introduction of tuberculin, proteins, etc.).