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.