active site

active site

n.

The part of an enzyme molecule at which catalysis of the substrate occurs.

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active site,

the place on the surface of an enzyme where its catalytic action occurs.

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active

not passive.

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active principle

the drugs or chemicals in a pharmaceutical preparation that exert an effect pharmacologically; as distinct from the inert fillers, wetting agents and other excipients also often included.

active site

that region of a protein, usually an enzyme, that binds to another molecule such as the substrate of the enzyme.

active transport

the movement of ions or molecules assisted by a carrier protein across the cell membranes and epithelial layers, usually against a concentration gradient, resulting directly from the expenditure of metabolic energy. For example, under normal circumstances more potassium ions are present within the cell and more sodium ions extracellularly. The process of maintaining these normal differences in electrolytic composition between the intracellular fluids is active transport. The process differs from simple diffusion or osmosis in that it requires the expenditure of metabolic energy.