Pyridoxine 5'-phosphate oxidase
| Pyridoxal 5'-phosphate synthase | |||||||||
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| Identifiers | |||||||||
| EC number | 1.4.3.5 | ||||||||
| CAS number | 9029-21-4 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / EGO | ||||||||
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| Search | |
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| PMC | articles |
| PubMed | articles |
| NCBI | proteins |
Pyridoxine 5’-phosphate oxidase is an enzyme that catalyzes several reactions in the vitamin B6 metabolism pathway. Pyridoxine-5-P oxidase catalyzes the terminal step (also the rate-limiting step) in vitamin B6 metabolism, the biosynthesis of pyridoxal-5’-phosphate, the biologically active form of vitamin B6 which acts as an essential cofactor. Pyridoxine 5’-phosphate oxidase is a member of the enzyme class oxidases, or more specifically, oxidoreductases. These enzymes catalyze a simultaneous oxidation-reduction reaction. The substrate oxidase enzymes is hydroxlyated by one oxygen atom of molecular oxygen. Concurrently, the other oxygen atom is reduced to water. Even though molecular oxygen is the electron acceptor in these enzymes’ reactions, they are unique because oxygen does not appear in the oxidized product.
Pyridoxine 5’-phosphate oxidase is a homodimer, or a molecule consisting of two identical polypeptide subunits. It is hypothesized that the two monomers are held together via disulfide bonds. There are also salt-bridge interactions between the two monomers. Each subunit tightly binds one molecule of pyridoxal 5'-phosphate tightly on each subunit. Both alpha-helices and beta-sheets are present in the protein motif, which is best described as a split-barrel structure. This structure is due, in part, to the disulfide bonds present in the secondary protein structure of this enzyme. Multiple thiol groups (-SH) indicate the presence of disulfide bonds in the structure of the molecule. This enzyme requires the presence of a cofactor, FMN (flavin mononucleotide). Cofactors are ions or coenzymes necessary for enzyme activity. The FMN is located in a deep cleft (formed by the two polypeptide subunits), and held in place by extensive hydrogen-bond interactions with the protein. In this particular case, the FMN helps the enzyme to bind the substrates. In the absence of pyridoxal 5’-phosphate (PLP), the active site of the enzyme is in an “open” conformation. Once substrate binds and is converted to PLP, the active site of the enzyme is in a partially “closed” conformation. Specific amino acid residues can form hydrogen bonds with the PLP, thus forming a lid that physically covers the active site, giving rise to the “closed” conformation.
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Wikipedia