Metabolic fluxes control

Thomas S, Fell DA. The role of multiple enzyme activation in metabolic flux control. Advan Enzyme Regul 1998 38 65-85. 

J. L. Galazzo and J. E. Bailey, Fermentation pathway kinetics and metabolic flux control in suspended and immobilized Saccharomyces cerevisiae. Enzyme Microb. Technol. 12(3), 162 172 (1990). 

Gnaiger, E. (1990). Concepts on efficiency in biological calorimetry and metabolic flux control. Thermochim. Acta 172,31-52. 

Zhou, L, and Zeng, A. (2015) Exploring lysine riboswitch for metabolic flux control and improvement of 1-Lysine synthesis in corynebacterium glutamicum. ACS Synth. Biol., 4 (6), 729-734,... 

L-hysine biosensors were developed that were based on the L-lysine-responsive C. glutamicum transcriptional regulator LysG and on the natural L-lysine riboswitches from E. coli and B. subtilis as well as on a synthetic riboswitch. While the L-lysine riboswitches were applied as L-lysine biosensors for on-demand metabolic flux control, the transcriptional regulator-based biosensors were used to screen libraries of L-lysine-producing strains (Figure 12.2). 

Riboswitches as Metabolite Sensors for on-Demand Metabolic Flux Control... 

In order to develop a rational approach to improving rates of metabolite production, it is necessary to consider the fate of the nutrients that are required for its synthesis. However, overcoming the major flux control points within a metabolic pathway may not lead to metabolite overproduction if the energetic consequences of the alteration are unfavourable to the organism. 

In both intermediate and maximum rates of respiration, control is distributed between several different steps, including the activity of the adenine nucleotide translocator (Groen et al., 1983). It is now recognized that the idea of a simple rate-limiting step for a metabolic pathway is simplistic and that control is shared by all steps although to different extents (Kacserand Bums, 1978 Fell, 1992). Each step in a pathway has a flux control coefficient (FCC) defined as ... 

Metabolic control analysis (MCA) assigns a flux control coefficient (FCC) to each step in the pathway and considers the sum of the coefficients. Competing pathway components may have negative FCCs. To measure FCCs, a variety of experimental techniques including radio isotopomers and pulse chase experiments are necessary in a tissue culture system. Perturbation of the system, for example, with over-expression of various genes can be applied iteratively to understand and optimize product accumulation. 

Adjunctive to flux control analysis, other components of metabolism that contribute to product accumulation are needed including (1) substrate/precursor pool sizes (metabolomics), (2) co-factor capacities (metabolomics), (3) gene expression profiles (transcriptomics and quanfifafive real-time PCR), (4) protein profiles (pro-... 

Transgenic E. coli accumulate comparatively low levels of carotenoids " compared to microbial algae, yeasts, and bacteria. Many efforts ° have focused on increasing accumulation by manipulation of factors affecting metabolic flux and metabolite accnmnlation (listed and discnssed in Sections 5.3.1.1 and 5.3.1.3 A) and have been reviewed." - " In bacterial systems, approaches to control can be categorized as either infrastructural (plasmids, enzymes, strains) or ultrastructural (media and feeding, enviromnent, precursor pools, substrate flux). 

SmoUce, C.D., Martin, V.J.J., and Keasling, J.D., Controlling the metabolic flux through the carotenoid pathway using directed mRNA processing and stabilization, Metabol. Eng. 3, 313, 2001. 

Metabolic Flux Analysis and Metabolic Control Analysis... 

After measuring the fluxes through the metabolic network, it is necessary to determine the extent to which each pathway or enzyme controls the net fluxes. Metabolic control analysis (MCA) is a technique used to elucidate how flux control is distributed in a metabolic network, thereby providing the information for identification of potential targets for metabolic engineering [8],... 

Fell DA, Thomas S. Physiologic control of metabolic flux the requirement for multisite modulation. Biochem J 1995 311 35-39. 

Signal transduction now ensures that information is selectively addressed to single cell types, where it is registered and transformed in a common manner - e. g., in the case of a human being which is composed of some trillions of cells [1]. Hereby metabolic fluxes or cell division are controlled efficiently. 

The riocus encodes the enzyme flavonoid 3 -hydroxylase (F3 H) [17, 18], and is an important controller of flux in the anthocyanin pathway in soybean seed coats (Fig. 4.1). F3 H diverts metabolic flux away from biosynthesis of orange (pelargoni-din) and blue (delphinidin) anthocyanins toward the red cyanidin-3-(9-glucoside, which is the main anthocyanin in the seed coats of black soybean [7, 8]. T increases the accumulation of delphidin-3-O-glucoside in black seed coats, even though it is not required for its biosynthesis [19]. Possible mechanisms for this include positive feedback, or the stabilization of the putative anthocyanin biosynthetic metabolon [20] by F3 Fl-derived membrane anchoring (Fig. 4.1). 

The formalized application of metabolic control analysis deals with several parameters (a) The flux control coefficient is defined as the fractional change in pathway flux... 

METABOLIC CONTROL ANALYSIS TOP-DOWN CONTROL ANALYSIS Metabolic flux,... 

FIGURE 15-34 Flux control coefficient, C, in a branched metabolic pathway. In this simple pathway, the intermediate B has two alternative fates. To the extent that reaction B —> E draws B away from the pathway A —> D, it controls that pathway, which will result in a negative flux control coefficient for the enzyme that catalyzes step B —> E. Note that the sum of all four coefficients equals 1.0, as it must. 

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