The protein part of an enzyme without the cofactor necessary for @C00874@. The cofactor can be a metal ion, an organic molecule (@C01126@), or a combination of both.
Source: PAC, 1994, 66, 2587. (Glossary of bioanalytical nomenclature - Part 1: General terminology, body fluids, enzymology, immunology (IUPAC Recommendations 1994)) on page 2593 [Terms] [Paper]