Protoporphyrin IX

Protoporphyrin IX is an organic compound, specifically a porphyrin, that plays an important role in living organisms as a precursor to other critical compounds like hemoglobin and chlorophyll. It is a deeply colored solid that is not soluble in water. The name is often abbreviated as PPIX.
Protoporphyrin IX contains a porphine core, a tetrapyrrole macrocycle with a marked aromatic character. Protoporphyrin IX is essentially planar, except for the N-H bonds that are bent out of the plane of the rings, in opposite (trans) directions. 
The general term protoporphyrin refers to porphine derivatives that have the outer hydrogen atoms in the four pyrrole rings replaced by four methyl groups (M), two vinyl groups (V), and two propionic acid groups (P). The Roman numeral "IX" indicates that these chains occur in the circular order MV-MV-MP-PM around the outer cycle. (The numbering of the variants is traditional and not entirely systematic.)
Natural occurrence.
The compound is encountered in nature in the form of complexes where the two inner hydrogen atoms are replaced by a divalent metal cation. When complexed with an iron(II) (ferrous) cation , the molecule is called heme. Hemes are prosthetic groups in some important proteins. These heme-containing proteins include hemoglobin, myoglobin, and cytochrome c. Complexes can also be formed with other metal ions, such as zinc.
Biosynthesis.
The compound is synthesized from acyclic precursors via a mono-pyrrole (porphobilinogen) then a tetrapyrrole (a porphyrinogen, specifically uroporphyrinogen III). This precursor is converted to protoporphyrinogen IX, which is oxidized to protoporphyrin IX. The last step is mediated by the enzyme protoporphyrinogen oxidase. 
Protoporphyrin IX is an important precursor to biologically essential prosthetic groups such as heme, cytochrome c, and chlorophylls. As a result, a number of organisms are able to synthesize this tetrapyrrole from basic precursors such as glycine and succinyl-CoA, or glutamic acid. Despite the wide range of organisms that synthesize protoporphyrin IX, the process is largely conserved from bacteria to mammals with a few distinct exceptions in higher plants.
In the biosynthesis of those molecules, the metal cation is inserted into protoporphyrin IX by enzymes called chelatases. For example, ferrochelatase converts the compound into heme B (i.e. Fe-protoporphyrin IX or protoheme IX). In chlorophyll biosynthesis, the enzyme magnesium chelatase converts it into Mg-protoporphyrin IX.
Described metalloprotoporphyrin IX derivatives.
The following metals are known to from Heme-like complexes when coordinated to PPX:
These compounds follow the naming convention [metal]-protoporphyrin IX, or protoporphyrin IX containing [metal]. 
Protoporphyrin IX reacts with iron salts in air to give the complex FeCl(PPIX).
Palepron is the disodium salt of protoporphyrin IX.