porphyrin A heterocyclic derivative of a porphin, which is composed of a tetrapyrrole ring structure. As such it is capable of combining with a variety of metals and so forms part of the structure of many important biological molecules, including haemoproteins, chlorophyll, vitamin B₁₂, and cytochromes.

porphyrin Any of a group of organic pigments characterized by the possession of a cyclic group of four linked nitrogen-containing rings (a tetrapyrrole nucleus), the nitrogen atoms of which are often coordinated to metal ions. Porphyrins differ in the nature of their side-chain groups. They include the chlorophylls, which contain magnesium; and haem, which contains iron and forms the prosthetic group of haemoglobin, myoglobin, and the cytochromes.

porphyrin (por-fi-rin) 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, myohaemoglobin, the cytochromes, and chlorophyll. See also protoporphyrin IX.

porphyrin A heterocyclic derivative of a porphin, which is composed of a tetrapyrolle ring structure. As such it is capable of combining with a variety of metals and so forms part of the structure of many important biological molecules, including haemoproteins, chlorophyll, vitamin B₁₂, and cytochromes.

porphyrin Heterocyclic derivative of a porphin, which is composed of four linked rings, each containing nitrogen (a tetrapyrrole ring structure). As such it is capable of combining with a variety of metals and so forms part of the structure of many important biological molecules, including haemoproteins, chlorophyll, cytochromes, and vitamin B₁₂.