Fig. 1.

a The B6 vitamers pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM) and the respective phosphate esters pyridoxal-5′-phosphate (PLP), pyridoxine-5′-phosphate (PNP) and pyridoxamine-5′-phosphate (PMP). b The deoxyxylulose 5-phosphate (DXP)-dependent and DXP-independent vitamin B6 biosynthetic routes and the salvage pathway for the interconversion of the B6 vitamers. Epd, erythrose 4-phosphate dehydrogenase; PdxB, 4-phosphoerythronate dehydrogenase; SerC, 3-phosphoserine aminotransferase; PdxA, 4-phosphohydroxy-l-threonine dehydrogenase; PdxJ, PNP synthase; Dxs, 1-deoxyxylulose 5-phosphate synthase; PdxH, PNP oxidase; PdxS (PLP synthase subunit) and PdxT (glutaminase subunit) form the PdxST PLP synthase complex; PdxK, PL kinase present in B. subtilis and E. coli; PdxY, PL kinase present in E. coli. PdxK from B. subtilis has PN, PL and PM kinase activity; PdxP, PNP and PLP phosphatase from S. meliloti; YbhA, PLP phosphatase from E. coli; PdxI, PL reductase from E. coli