 Many porphyrin-containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins.Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase.The word "heme" is derived from Greek "haima" meaning "blood".