Hydroxymethylbilane, also known as preuroporphyrinogen, is an organic compound that occurs in living organisms during the synthesis of porphyrins, a group of critical substances that include haemoglobin, myoglobin, and chlorophyll. The name is often abbreviated as HMB.
Structure
The compound is a substituted bilane, a chain of four pyrrole rings interconnected by methylene bridges−CH2−. The chain starts with a hydroxymethyl group −CH2−OH and ends with a hydrogen, in place of the respective methylene bridges. The other two carbon atoms of each pyrrole cycle are connected to an acetic acid group −CH2−COOH and a propionic acid group −CH2−CH2−COOH, in that order.[1]
Metabolism
HMB is generated from four molecules of porphobilinogen by the enzyme porphobilinogen deaminase in the overall reaction:[2][3]
The enzyme uroporphyrinogen III synthase catalyses the cyclisation reaction of hydroxymethylbilane into uroporphyrinogen III via a spiro intermediate which allows one of the pyrrole rings to convert its initial acetate to propionate configuration into a propionate-acetate one.[2][4][5]
