Wild-type transketolase

Transketolase (wild type) reconstituted with 4 -deamino-ThDP 9.5 + 0.1 X 10-5... 

Corynebacterium utamicum transketolase mutants, which contained a plasmid encoding the C. ammoniagenes rib operon, demonstrated superior riboflavin production over transketolase wild-type host strains provided with the same plasmid. The experiments were carried out in test tubes reaching 41 and 108 mg 1 riboflavin with the transketolase wild type and mutant strain, respectively. It is not clear to which extent these results are relevant for industrial high-intensity fed-batch fermentation runs. 

To improve percent conversion and product purity, it was essential to remove the rate-limiting character of DHQ synthase. Plasmid pi 136 (42) was created by insertion of a 1.65 kb aroB fragment into the transketolase and DAHP synthaseencoding plasmid pKD130A. H NMR analysis of the culture supernatant of AB2834 ro /pKD136 indicated that the strain synthesized 30 mM DHS from 56 mM D-glucose (42). No other intermediates from the common pathway were detected in the culture supernatant. Because DHQ was never detected in the culture supernatant, wild-type levels of DHQ dehydratase were apparently adequate to prevent intracellular accumulation and subsequent exportation of DHQ. 

Further improvement in production performance was achieved with a strain containing a tkt mutant allele (instead of the wild type) with drastically reduced enzymatic transketolase activity [180]. Transketolase is a key enzyme in the pentose phosphate pathway delivering ribulose-5-P and ribose-5-P, which are important building blocks for riboflavin biosynthesis. Presumably, the mutation impedes drainage of the pentose phosphate pathway intermediates back toward... 

---