Pyridoxal Reductase, PdxI, Is Critical for Salvage of Pyridoxal in Escherichia coli.

Pyridoxal 5'-phosphate (PLP) is the biologically active form of vitamin B and an essential cofactor in all organisms. In , PLP is synthesized via the deoxyxylulose 5-phosphate (DXP)-dependent pathway that includes seven enzymatic steps and generates pyridoxine 5'-phosphate as an intermediate. Additionally, is able to salvage pyridoxal, pyridoxine, and pyridoxamine B vitamers to produce PLP using kinases PdxK/PdxY and pyridox(am)ine phosphate oxidase (PdxH). We found that strains blocked in PLP synthesis prior to the formation of pyridoxine 5'-phosphate (PNP) required significantly less exogenous pyridoxal (PL) than strains lacking and identified the conversion of PL to pyridoxine (PN) during cultivation to be the cause. Our data showed that PdxI, shown to have PL reductase activity , was required for the efficient salvage of PL in The strains converted exogenous PL to PN during growth, while mutants did not. In total, the data herein demonstrated that PdxI is a critical enzyme in the salvage of PL by The biosynthetic pathway of pyridoxal 5'-phosphate (PLP) has extensively been studied in , yet limited information is available about the vitamin B salvage pathway. We show that the protein PdxI (YdbC) is the primary pyridoxal (PL) reductase in and is involved in the salvage of PL. The orthologs of PdxI occur in a wide range of bacteria and plants, suggesting that PL reductase in the B salvage pathway is more widely distributed than previously expected.