Jl. Lu et Jc. Liao, METABOLIC ENGINEERING AND CONTROL ANALYSIS FOR PRODUCTION OF AROMATICS - ROLE OF TRANSALDOLASE, Biotechnology and bioengineering, 53(2), 1997, pp. 132-138
Aromatic metabolites in Escherichia coli and other microorganisms are
derived from two common precursors: phosphoenolpyruvate (PEP) and eryt
hrose 4-phosphate (E4P). During growth on glucose, the levels of both
E4P and PEP are insufficient for high throughput of aromatics because
of the low carbon flux through the pentose pathway and the use of PEP
in the phosphotransferase system. It has been shown that transketolase
and PEP synthase are effective in relieving this limitation and promo
ting high throughput of aromatics. To determine whether transaldolase,
another E4P-producing enzyme, is also a limiting factor in directing
carbon flux to the aromatic pathway, E. coli transaldolase gene (tal)
was cloned and overexpressed in an aroB strain which excretes 3-deoxy-
D-arabinoheptulosonate-7-phosphate (DAHP), the first intermediate in t
he aromatic pathway. We found that overexpression of transaldolase did
significantly increase the production of DAHP from glucose. This resu
lt further supports the contention that the supply of E4P is limiting
when glucose is the carbon source. However, overexpression of transald
olase in strains which already overexpress transketolase did not show
a further increase in production of aromatics. This result was attribu
ted to the saturation of E4P supply when TktA was overexpressed. The f
lux control of DAHP production was discussed on the basis of Metabolic
Control Analysis. (C) 1997 John Wiley & Sons, Inc.