Why superoxide imposes an aromatic amino acid auxotrophy on Escherichia coli - The transketolase connection

The lack of superoxide dismutase and the consequent elevation of [O-2(-)] i mposes, on Escherichia coli, auxotrophies far branched chain, sulfur-contai ning, and aromatic amino acids. The former two classes of auxotrophies have already been explained, whereas the third is explained herein. Thus O-2(-) is shown to interfere with the production of erythrose-4-phosphate, which is essential for the first step of the aromatic biosynthetic pathway. It do es so by oxidizing the 1,2-dihydroxyethyl thiamine pyrophosphate; intermedi ate of transketolase and inactivating this enzyme.