Metabolic flow

Westerhoff, H.F. Welch, G.R. (1992). Enzyme organization and the direction of metabolic flow Physiochemical considerations. Curr. Topics Cell. Reg. 33, 361-390. 

Steven Rose That still won t tell you the metabolic flow - it will be one step better than this - but it won t tell you the flow. 

Accordingly, a strain of E. coli was first engineered to produce elevated levels of DHQ by increasing the levels of certain key enzymes transketolase, 3-deoxy-D-arabino-heptulosonic acid 7-phospate (DAHP) synthase, and DHQ synthase. Also, the strain has reduced levels of DHQ dehydratase, which if present would divert some of the metabolic flow into the biosynthesis of aromatic amino acids its blockage results in higher production of quinic acid. 

Regulation is crucial in the biosynthesis of the nitrogen-containing compounds. Because each amino acid and each nucleotide is required in relatively small amounts, the metabolic flow through most of these pathways is not nearly as great as the biosynthetic flow leading to carbohydrate or fat in animal tissues. Because the different amino acids and nucleotides must be made in... 

If the equilibrium constant is known, this relationship can be used to check the validity of the kinetic constants which have been determined. In general, the equilibrium will favour the metabolically important direction. However, it should be noted that the direction of metabolic flow in cell systems will also be dependent of the concentrations of substrate and products. 

In a branched-chain anabolic pathway, end-product inhibition usually regulates the first enzyme after the branchpoint (fig. I l, 8b). This arrangement leads to control of either pathway after the branchpoint (fig. 11.8b). If the supply of the branchpoint substrate (D in fig. 11.8b) is limiting, the inhibition of one pathway after the branchpoint can increase the metabolic flow of the other pathway. This effect is often highly significant. Apropos of this point, anabolic sequences frequently arise as branchpoints from catabolic pathways (fig. 11.9). In such instances the control factors affect whether a catabolic intermediate is further degraded or serves as a substrate for biosynthesis. 

For an effective symbiotic state, the plant and the microsymbiont must maintain a constant metabolic flow of carbon and nitrogen. While the bacteroids function as an engine for nitrogen fixation the fuel comes from the plant. Dicarboxylic acids are the primary carbon sources fed to the bacteroids by the plant. This unidirectional flow of carbon must be controlled by the PBM. Recently, several specific carbon and amino acid transport systems have been identified in the PBM using isolated peribac-teroid units (PBU Day et al., 1990). Thus, in order for the host plant to house endosymbiotic bacteria and support their metabolic needs, a number of nodulin genes must be induced to support the ontogeny and function of the nodules. 

Ferrance JP, Goel A, Ataai MM (1993), Utilization of glucose and amino acids in insect cell cultures quantifying the metabolic flows within the primary pathways and medium development, Biotechnol. Bioeng. 42 697-707. 

Ohara, H., Owaki, M., and Sonomoto, K. 2007. Calculation of metabolic flow of xylose in Lactococcus lactis. J. Biosci. Bioeng.,103, 92-94. 

Directing metabolic flow from a common biosynthetical intermediate to the desired product by overexpressing the branchpoint enzyme. 

Steady-state metabolic flows./ depend on the total concentrations of the enzymes Ek, and flow control coefficients ( jj are defined by... 

Fluxes of many different solutes occur across biological membranes. Inward fluxes move mineral nutrients into cells, while certain products of metabolism flow out of cells. The primary concern in this section is the passive fluxes of ions toward lower chemical potentials. First, we indicate that the passive flux density of a solute is directly proportional to the driving force causing the movement. Next, the driving force is expressed in terms of the relevant components of the chemical potential. We then examine the consequences of electroneutrality when there are simultaneous passive fluxes of more than one type of ion. This leads to an expression describing the electrical potential difference across a membrane in terms of the properties of the ions penetrating it. 

L-Methionine (Met) conversion to Cys is impaired under stress, such as in premature infants or AIDS patients. Thus, the metabolic flow through the trans-sulphuration pathway may be inadequate to meet the Cys demand under critical conditions. 

Figure 36-1. The metabolic flow during the fed state. Increased blood glucose triggers release of insulin and a decrease in the release of glucagon and lipolytic hormones. 

Figure 36-2. The metabolic flow following a postfeeding fast. Blood glucose levels begin to decrease, triggering homeostatic mechanisms to prevent it from decreasing dramatically.

Figure 36-5. The metabolic flow during prolonged starvation. The brain adapts to use ketone bodies as a source of energy, thus decreasing its utilization of glucose.

Most amino-acid metabolism produces simple metabolic products that readily flow into the metabolic flow. 

CorneKssen A.J., Dankelman J., VanBavel E., and Spaan J.A. Balance between myogenic, flow-dependent, and metabolic flow control in coronary arterial tree a model study. Am. J. Physiol. Heart Circ. Physiol. 282 H2224-H2237,2002. 

It is customary to consider the metabolic flow processes that occur in living organisms as consisting of chemical reactions on the one hand, and transport reactions on the other. The chemical reactions are defined as the processes of... 

Altering Nutrient Uptake or Metabolic Flow. Alteration of nutrient uptake or metabolic flow can be done not only by genetic manipulation but also by using inhibitors—simple chemicals or physical factors such as light or temperature. 

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