I understand that Porphyrin is defined as 4 pyrole rings linked by methenyl bridges. When this porphyrin ring is associated with a Ferrous ion (Fe 2+) we get the Heme molecule. However my book mentions that Heme is a complex of Protoporhyrin IX and Ferrous ion. So what is the difference between a Porphyrin ring and a Protoporphyrin ring?

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    $\begingroup$ There's no difference, protoporphyrin IX is one of a large number of porphyrins. What you think of as porphyrin is actually porphine, a parent compound of the group, a "core" of protoporphyrin IX. $\endgroup$
    – Mithoron
    May 13 at 16:58

1 Answer 1


From here:

Protoporphyrin is a derivative of porphyrin. The key difference between porphyrin and protoporphyrin is that porphyrin is a group of aromatic chemicals which has four modified pyrrole subunits interconnected to each other, whereas protoporphyrin is a derivative of porphyrin which has propionic acid groups.

Protoporphyrine contains porphine as core which is the simplest of the porphyrin chain. Picture from Wikipedia:

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