apoenzyme

The catalytically inactive protein portion of an enzyme that remains when the prosthetic group or *cofactor has been removed. Examples of enzymes needing both apoenzyme and cofactor for catalytic activity include: alcohol dehydrogenase, which requires zinc ions; kinases, which require magnesium or manganese ions; and the cytochromes, which require ferrous, Fe (II), or ferric, Fe(III), ions. See also holoenzyme .