n. The component of hemoglobin (and other hemoproteins) responsible for binding oxygen, consists of an iron ion that binds oxygen and a porphyrin ring that binds the globin molecules; one molecule binds one molecule of oxygen.
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n. a complex red organic pigment containing iron and other atoms to which oxygen binds
Word Usage
"They put a smaller structure inside it called a heme, a large flat molecule that is the active part of hemoglobin."