5. A small molecule that when bound to the allosteric site of an enzyme causes either a decrease or an increase in the activity of the enzyme.

• 别（变）构酶：这种酶除了有活性中心外，还有一个别构中心，当专一性的代谢物非共价的结合到别构中心上时，它的催化活性即发生改变。收藏指正