Cross references: Globin Muscle Innervation
Motor Neuron Evolution Motor Nerve Organization
Medial Motor Column Fast vs. Slow Twitch Muscles
British English) or heme (American English) is a chemical compound of a type known as a prosthetic group consisting of an Fe2+ (ferrous) ion contained in the centre of a large heterocyclic organic ring called a porphyrin, made up of four pyrrolic groups joined together by methine bridges. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins. Hemes are most commonly recognized in their presence as components of hemoglobin, the red pigment in blood, but they are also components of a number of other hemo-proteins such as myoglobin, cytochrome, endothelial nitric oxide synthase, catalase, etc.
The reference refers to "hemoglobin, the red pigment in blood", but it does not say that all hemes are red.