We studied the biosynthetic route of thiamin in Saccharomyces cerevisiae to
see whether the route differed under aerobic and anaerobic conditions.
Histidine and pyridoxine are the precursors of the pyrimidine moiety of thi
amin under aerobic conditions. Formate is incorporated into the pyrimidine
via histidine, The incorporation of [C-13]formate and [5'-H-2(2)]pyridoxine
into the pyrimidine was examined under anaerobic conditions. The labels fr
om [C-13]formate and [5'-H-2(2)]pyridoxine were not incorporated into the p
yrimidine under anaerobic conditions, indicating that the biosynthetic path
way of the pyrimidine differed from that under aerobic conditions.
On the other hand, [N-15]glycine was incorporated into the thiazole under b
oth anaerobic and aerobic conditions. The biosynthetic pathway of the thiaz
ole was therefore unaltered by the O-2 concentration.