Increasing the flux in metabolic pathways: A metabolic control analysis perspective

Abstract

The problems of engineering increased flux in metabolic pathways are analyzed in terms of the understanding provided by metabolic control analysis. Over‐expression of a single enzyme is unlikely to be effective unless it is known to have a high flux control coefficient, which can be used as an approximate predictive tool. This is likely to rule out enzymes subject to feedback inhibition, because it transfers control downstream from the inhibited enzyme to the enzymes utilizing the feedback metabolite. Although abolishing feedback inhibition can restore flux control to an enzyme, it is also likely to cause large increases in the concentrations of metabolic intermediates. Simultaneous and coordinated over‐expression of most of the enzymes in a pathway can, in principle, produce substantial flux increases without changes in metabolite levels, though technically it may be difficult to achieve. It is, however, closer to the method used by cells to change flux levels, where coordinated changes in the level of activity of pathway enzymes are the norm. Another option is to increase the demand for the pathway product, perhaps by increasing its rate of excretion or removal. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:121–124, 1998.

Lifetime performance in foraging honeybees: behaviour and physiology

“…However, proteomic analysis revealed an increase in aldolase abundance in flight muscles of mature foragers compared to hive bees. The aldolase step in glycolysis is generally thought to be a near-equilibrium reaction and thus its contribution in determining overall flux through pathways is somewhat controversial (Brooks, 1996;Fell, 1998;Pierce and Crawford, 1997). However, there is M.-P. Schippers and others some evidence for near-equilibrium steps of pathways affecting flight metabolism (Coelho and Mitton, 1988;Harrison et al, 1996).…”

Regulation of Gene Expression in Flux Balance Models of Metabolism

“…Regulatory modeling is also bene"cial to the "eld of metabolic engineering. Using metabolic control analysis, it has been demonstrated that control of biosynthetic #uxes depends on multiple enzymes (Fell, 1998;McAdams & Arkin, 1998). The engineering of cell regulation, rather than of the expression of several related genes, may be a more e$cient use of an organism's metabolism to produce a desired product.…”

“…Kinetic theory may also be combined with Boolean logic as in a hybrid model of the lambda phage (McAdams & Shapiro, 1995), using fuzzy logic as has been done with E. coli core metabolism (Lee et al, 1999) or in conjunction with cybernetic principles (Guardia et al, 2000;Varner, 2000). Other approaches to the analysis of genetic regulatory circuits include the use of fractal kinetic theory (Savageau, 1998) and stochastic modeling techniques (McAdams & Arkin, 1997, 1998Carrier & Keasling, 1999). Detailed deterministic and stochastic models require extensive information, such as temperature, substrate availability, the presence of signaling molecules, and other environmental parameters, many of which have yet to be completely speci"ed.…”

Control of the threonine-synthesis pathway in Escherichia coli: a theoretical and experimental approach

“…The reasons for this have been explored theoretically, particularly through the theory of metabolic control analysis, which has given reasons for doubting that large increases in flux could generally be obtained simply by abolishing feedback inhibition [3] or over-expressing a single pathway enzyme [3][4][5][6]. These basic propositions have been confirmed experimentally (e.g.…”