Vitamin B-6 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 synthesise d de novo by a pathway that is thought to involve the condensation of 4-(ph osphohydroxy)-L-threonine and 1-deoxy-D-xylulose, catalysed by the enzymes PdxA and PdxJ, to form either pyridoxine (vitamin Bs) or pyridoxine 5'-phos phate (PNP), Here we show that incubation of PdxJ with PdsA, 4-(phosphohydr oxy)-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 characteris ed by (i) cochromatography with an authentic standard, (ii) conversion to p yridoxine 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 res ults clarify the previously unknown role of PdxJ in the de novo PLP biosynt hetic 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 Federa tion of European Biochemical Societies.