The metabolic pathway for L-tryptophan synthesis is limited by the availability of reducing equivalents. Increasing the flux of NADPH through transhydrogenase expression overcomes the cofactor imbalance that restricts high-yield fermentation.

The keywords indicate that existing enzyme variants limit the efficient conversion of precursors into L-tryptophan. Improving these specific enzymatic bottlenecks increases the overall rate and yield of the biosynthetic pathway.

The primary bottleneck in L-tyrosine biosynthesis is the limited availability of metabolic intermediates and cofactor imbalance. Increasing this flux overcomes rate-limiting steps to achieve industrial-scale yields.