Isoenzymes, or isoforms, are different molecular forms of the same enzyme that catalyze the same chemical reaction but differ in amino acid sequence or regulatory properties. They allow tissue-specific expression and can be distinguished by electrophoresis or other biochemical methods. Clinically, isoenzymes help in diagnosis by indicating the source of tissue damage (e.g., CK-MB in myocardial infarction). This functional similarity with structural variation is key to their identification and use in medicine.

Reference: Robbins Basic Pathology, Kumar, Abbas, Aster, 10th Edition.