AN ESCHERICHIA-COLI K-12 TKTA TKTB MUTANT DEFICIENT IN TRANSKETOLASE ACTIVITY REQUIRES PYRIDOXINE (VITAMIN-B-6) AS WELL AS THE AROMATIC-AMINO-ACIDS AND VITAMINS FOR GROWTH

We show that a tktA tktB double mutant, which is devoid of the two known transketolase isoenzymes of Escherichia coli K-12, requires pyridoxine (vitamin B-6) as well as the aromatic amino acids and vitamins for growth. This pyridoxine requirement can also be satisfied by 4-hydroxy-L-threonine or glycolaldehyde. These results provide direct evidence that D-erythrose-4-phosphate is a precursor of the pyridine ring of pyridoxine. In addition. they show that the two major E. coli transketolase isoenzymes are not required for the biosynthesis of D-1-deoxylulose, which is thought to be another precursor of pyridoxine.