n. one of a number of pigments derived from *porphin, which are widely distributed in living things. All porphyrins form chelates with iron, magnesium, zinc, nickel, copper, and cobalt. These chelates are constituents of *haemoglobin, *myoglobin, the *cytochromes, and chlorophyll, and are thus important in many oxidation/reduction reactions in all living organisms. See also protoporphyrin IX.
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