Vitamin B6 biosynthesis:: formation of pyridoxine 5′-phosphate from 4-(phosphohydroxy)-L-threonine and 1-deoxy-D-xylulose-5-phosphate by PdxA and PdxJ protein

In Escherichia coli the coenzyme pyridoxal 5'-phosphate (PLP) is synthesised de novo by a pathway that is thought to involve the condensation of 4-(phosphohydroxy)-L-threonine and 1-deoxy-D-xylulose, catalysed by the enzymes PdxA and PdxJ, to form either pyridoxine (vitamin Bs) or pyridoxine 5'-phosphate (PNP), Here we show that incubation of PdxJ with PdsA, 4-(phosphohydroxy)-L-threonine, NAD and 1-deoxy-D-xylulose -5-phosphate, but not 1-deoxy-D-xylulose, results in the formation of PNP, The PNP formed,vas characterised by (i) cochromatography with an authentic standard, (ii) conversion to pyridoxine by alkaline phosphatase treatment, and (iii) UV and fluorescence spectroscopy. Furthermore, when [2-C-14]1-deoxy-D-xylulose-5-phosphate was used as a substrate, the radioactivity,vas incorporated into PNP, These results clarify the previously unknown role of PdxJ in the de novo PLP biosynthetic pathway, The sugar used as substrate by PdxJ is 1-deoxy-D-xylulose-5-phosphate rather than the previously assumed 1-deoxy-D-xylulose. The first vitamin B-6 vitamer synthesised is PNP, and not pyridoxine. (C) 1999 Federation of European Biochemical Societies.