heme

noun

1. (countable, uncountable)The component of hemoglobin (and other hemoproteins) responsible for binding oxygen. It consists of an iron ion that binds oxygen and a porphyrin ring that binds the globin molecules; one molecule binds one molecule of oxygen.

   “The binding of oxygen to the iron molecule causes the hemoglobin molecule to undergo conformational changes that affect the binding of oxygen to other heme sites.”

   “Impossible's breakthrough was in discovering that meat's essence comes from heme—the iron-rich molecule in blood that carries oxygen and is responsible for the deep-red color.”