activation (redirected from activation unit)

activation /ac·ti·va·tion/ (ak?ti-va´shun)

1. the act or process of rendering active.

2. the transformation of a proenzyme into an active enzyme by the action of a kinase or another enzyme.

3. the process by which the central nervous system is stimulated into activity through the mediation of the reticular activating system.

4. the deliberate induction of a pattern of electrical activity in the brain.

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allosteric activation  increase in enzyme activity by binding of an effector at an allosteric site that affects binding or turnover at the catalytic site.

contact activation  initiation of the intrinsic pathway of coagulation through interaction of coagulation factor XII with various electronegative surfaces.

lymphocyte activation  stimulation of lymphocytes by antigen or mitogens resulting in macromolecular synthesis (RNA, protein, and DNA) and production of lymphokines, followed by proliferation and differentiation of the progeny into various effector and memory cells.

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activation

the process of activating.

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activation analysis

a method of analyzing the content of elements in samples of biological material. The sample is bombarded with nuclear particles and the elements in it measured by the radiation emitted by their radioactive daughter products. Called also radioactivation analysis.

activation energy

the difference in energy between the ground state of the reactants in a reaction and the point of maximum energy or transition state of the reactions. Usually lowered by enzyme catalysts.

activation factor

see hageman factor.

activation unit

the combination of complement (C4, C2 and C3) that binds to the antigen-antibody complex in the initial reaction step in the classical pathway of complement activation. See also complement.

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activation Hematology See Plasminogen activation Immunology Lymphocyte activation, see there. See Complement activation, Macrophage activation Neurology The stimulation of a nerve to a level high enough to kick over its action potential.