4-O-PHOSPHORYL-L-THREONINE, A SUBSTRATE OF THE PDXC(SERC) GENE-PRODUCT INVOLVED IN VITAMIN-B-6 BIOSYNTHESIS

The Escherichia coli pdxC(serC) gene codes for a transaminase (EC 2.6. 1.52). The gene is involved in both pyridoxine (vitamin B-6) and serin e biosynthesis and was overexpressed as a MalE/PdxC(SerC) fusion prote in. The fusion protein was purified by affinity chromatography on an a mylose resin and hydrolyzed in the presence of protease factor Xa. Bot h the fusion protein and the PdxC(SerC) protein were characterized (K- M value, turnover number, optimum pH). Both enzymes used 4-O-phosphory l-L-threonine rather than 4-hydroxy-L-threonine as a substrate indicat ing that the phosphorylated rather than the non-phosphorylated amino a cid is involved in pyridoxine biosynthesis, Pyridoxal phosphate was sh own to be the cofactor for both enzymes and therefore seems to be invo lved in its own biosynthesis.