A nonprotein component of some enzymes that is necessary for catalytic activity. Cofactors may be either metal ions or coenzymes. They are usually heat stable, unlike most enzyme proteins, which are denatured by heat. Many enzymes require metal ions as cofactors. Examples are ferredoxin, which requires ferrous, Fe(II), and ferric, Fe(III), ions, and alcohol dehydrogenase, which requires zinc ions. In some enzymes the metal ion is the primary catalytic centre, while in others it may act to bind enzyme and substrate together, or to stabilize the enzyme in its catalytically active conformation. See also prosthetic group , apoenzyme , holoenzyme. |
