Abstract
There are divergent pathways for de novo pyridoxine biosynthesis. Yeasts(fission and budding yeasts) have a different pathway from that of Escherichia coli. We have examined possible precursors in the pathway of yeast. Based on the result that an L-leucine-requiring mutant strain of fission yeast (Scbizosaccharomyces pombe) showed correlation between concentration of L-leucine and productivity of vitamin B_6, we have examined 2-isopropylmaleate and 3-isopropylmaleate, intermediates of L-leucine biosynthesis in the yeast, as the candidate of precursor of pyridoxine biosynthesis. Competitive experiments with [U-^<13>C]D-glucose showed that the two compounds may not be the precursor. 2-Oxoisovalerate, L-valine and L-isoleucine inhibited incorporation of ^<13>C intO pyridoxine in the competitive experiment. Thus, 2-oxoisovalerate or its related compound was suggested to be the candidate of the precursor.
