InterPro domain: IPR011576

Pyridoxamine 5'-phosphate oxidase (PNPOx; 1.4.3.5 ) is a FMN flavoprotein that catalyses the oxidation of pyridoxamine-5-P (PMP) and pyridoxine-5-P (PNP) to pyridoxal-5-P (PLP). This reaction serves as the terminal step in the de novo biosynthesis of PLP in Escherichia coli and as a part of the salvage pathway of this coenzyme in both E. coli and mammalian cells [ 1 , 2 ]. The binding sites for FMN and for substrate have been highly conserved throughout evolution.

This entry represents a domain with putative PNPOx (Pyridoxamine 5'-phosphate oxidase) function. The domain was initially predicted to encode pyridoxamine 5'-phosphate oxidase, based on sequence similarity. However, there is no experimental data to validate the predicted activity and purified proteins, such as Q06199 and its paralogs, do not possess this activity, nor do they bind to flavin mononucleotide (FMN). To date, the only time functional oxidase activity has been experimentally demonstrated is when the sequences contain both PF01243 and PF10590 . Moreover, some of the family members that contain both domains have been shown to be involved in phenazine biosynthesis. While some molecular function has been experimentally validated for the proteins containing both domains, the role performed by each domain on its own is unknown [ 3 ].

1. Structure and mechanism of Escherichia coli pyridoxine 5'-phosphate oxidase. Biochim. Biophys. Acta 1647, 76-82
2. Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. Protein Sci. 12, 1455-63
3. Experimental Evidence for a Revision in the Annotation of Putative Pyridoxamine 5'-Phosphate Oxidases P(N/M)P from Fungi. PLoS ONE 10, e0136761