Methaemoglobin

Part of speech: noun

Definitions

1. A form of hemoglobin in which the iron is oxidized, rendering it incapable of transporting oxygen effectively
2. A type of hemoglobin characterized by iron in the ferric state, leading to reduced oxygen-carrying capacity in the blood
3. An altered form of hemoglobin that results from oxidation, which diminishes its ability to bind and release oxygen efficiently

Etymology: Methaemoglobin is built from two Greek elements and a shorter English word. The "meta-" prefix comes from Greek "metá", which in chemistry signals a change or a further stage, while "haemoglobin" is itself a compound of the Greek "haîma" (blood) and the Latin "globus" (sphere, ball), with the "-in" ending borrowed from the Latin "-inus" that chemists use for protein names. Put together, "methaemoglobin" names a modified form of haemoglobin, the oxygen-carrying protein in red blood cells. The word's meaning rests on the idea of transformation rather than on a sense of "beyond" or "after." When the iron at the centre of haemoglobin is oxidized from its usual ferrous state to the ferric state, the molecule changes its chemistry and loses much of its ability to bind and carry oxygen. The prefix therefore marks a changed version of the same molecule, not a different substance altogether.