Physical and enzymological interaction of Bacillus subtilis proteins required for de novo pyridoxal 5′-phosphate biosynthesis

Bacillus subtilis synthesizes pyridoxal 5'-phosphate, the active form of vitamin B-6, by a poorly characterized pathway involving the yaaD and yaaE genes. The pdxS (yaaD) mutant was confirmed to be a strict B-6 auxotroph, but the pdxT (yaaE) mutant turned out to be a conditional auxotroph depending on the availability of ammonium in the growth medium. The PdxS and PdxT proteins copurified during affinity chromatography and apparently form a complex that has glutaminase activity. PdxS and PdxT appear to encode the synthase and glutaminase subunits, respectively, of a glutamine amidotransferase of as-yet-unknown specificity essential for B-6 biosynthesis.