Ectoenzyme

Part of speech: noun

Definitions

1. An enzyme anchored to the outer membrane of a cell that acts on substrates in the extracellular environment
2. A membrane-bound protein catalyst located on a cell's surface that performs enzymatic reactions on molecules outside the cell
3. An enzyme fixed to the external surface of a cell that breaks down or transforms substances in the surrounding medium

Etymology: "Ectoenzyme" is a technical coinage built from two parts: "ecto-", from Greek "ektos" meaning "outside," and "enzyme," a term from the German "Enzym," itself coined in the 1800s from Greek roots meaning "in leaven." Put together, the name describes an enzyme that acts outside the cell that produced it, as opposed to one that works within the cell. The prefix "ecto-" appears across biology and medicine, in words such as "ectoderm," the outer embryonic layer, and "ectoparasite," an organism living on the outside of a host. Its use here follows the same pattern: the enzyme is located on the cell's outer surface or released into its surroundings, where it can break down material before that material ever enters the cell.