Isoenzyme

Part of speech: noun

Definitions

1. A variant of an enzyme that, while differing in structure, catalyzes the same chemical reaction within biological systems
2. Molecular forms of an enzyme that differ in amino acid sequence yet catalyze identical biochemical reactions in living organisms
3. A specific form of an enzyme that varies in its amino acid composition but retains the ability to facilitate the same biochemical processes in organisms

Etymology: Ancient Greek "ísos" meant "equal," and it gives English the prefix "iso-," as in "isotope" and "isobar," where something is the same or uniform. Joined to "enzyme," it names a striking pairing: enzymes that differ at the molecular level yet drive the same reaction. "Enzyme" is itself a modern coinage built from Greek elements meaning roughly "in leaven," a nod to the yeast fermentation that early researchers studied. The compound is therefore literal: "iso-" marks the equal action, and "enzyme" marks the protein-based catalyst it describes.