heme

1. (biochemistry) 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.Examples: "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."countableuncountable