Substrate supply

Figure 13. The Gibbs energy available from a reaction, A B, depends on its displacement from equilibrium when IB)/IA) = K. The AC value is plotted against the mass-action ratio, and this is the value when B1/ A] is maintained constant in the steady state if the rate of substrate supply and substrate removal is constant.

The signiflcance of toxic metabolites is important in diverse metabolic situations (a) when a pathway results in the synthesis of a toxic or inhibitory metabolite, and (b) when pathways for the metabolism of two (or more) analogous substrates supplied simultaneously are incompatible due to the production of a toxic metabolite by one of the substrates. A number of examples are provided to illustrate these possibilities that have achieved considerable attention in the context of the biodegradation of chlorinated aromatic compounds (further discussion is given in Chapter 9, Part 1) ... 

Israel, Y. and Orrego, H. (1981). Hepatocyte demand and substrate supply as factors in susceptibility to alcoholic liver injury pathogenesis and prevention. J. Clin. Gastroenterol. 10, 355-373. 

The addition of ethanolamine to the enzyme-coenzyme complex resulted in greater than 90% loss in signal intensity. When the substrate supply was exhausted, the original ESR spectrum reappeared slowly but did not regain its full intensity after 30 minutes. Under the experimental... 

Because the gaseous part of the reactor space was large enough for such a tiny amount of liquid decalin, the substrate supply to the catalyst surface was apt to become deficient especially after the reaction time elapsed. As a consequence, the reaction rate decreased rather rapidly in this sand-bath state. 

The brain has an absolute dependence on the blood for its immediate supply of oxygen and energy substrates. Interruption of oxygen or substrate supply by compromise of pulmonary or cardiovascular function or metabolic factors results in encephalopathy and, if prolonged, neuronal cell death. The brain uses approximately 20% of the total oxygen supply of the body. While glucose remains the primary energy substrate for the brain, alternative substrates maybe used under certain circumstances (see Ch. 31). 

The liver forms increased amounts of glycogen and fats from the substrates supplied. Glycogen is stored, and the fat is released into the blood in very low density lipoproteins (VLDLs). 

Applied biocatalysis can be defined as the application of a biocatalyst to achieve a desired conversion under controlled conditiotts in a bioieactor. A biocatalyst can either be an enzyme, an enzyme complex, a cell organelle or a whole cell. The latter can be viable growing or non-growing or non-viable. Fttrihermoie, a biocatalyst can be free or immobihzed and this has far-reaching cortsequences, not only with respect to substrate supply and mass transfer in general, but sometimes also, in case of viable cells, with... 

An alternative process using immobilised thermolysin in column reactors with substrates supplied in ethyl acetate—water as the solvent seems to be feasible. 

Fatty Acid Biosynthesis Is Limited by Substrate Supply... 

From the above simple steady-state diagram, point B is unstable because for any concentration change slightly to the right of B, the rate of substrate consumption is smaller than the rate of substrate supply. Therefore the concentration continues to increase and the system does not go back to the steady state B. Similarly, as the concentration is lowered slightly to put the system to the left of its steady-state point B, the rate of substrate supply is smaller than the rate of consumption and therefore the concentration continues to decrease and never returns to the steady state B. This makes the steady state B unstable. 

Freeman, C., and M. A. Lock. 1995. The biofilm polysaccharide matrix-a buffer against changing organic substrate supply Limnology and Oceanography 40 273-278. 

Similar to what was shown for growth, some models establish a linear relationship between the specific death rate (kj) and an autoinhibitory product synthesis (Lee et al., 1995). This autoinhibitory product is represented by the expression Xv/D, where Xv is a viable cells concentration, measured in terms of cell number per volume, and D is the specific feed rate that plays the part of substrate supply to the culture. By setting kj/px as a function of Xt/D (where Xt is a total cell concentration) it is possible to build up a more robust model that can fit a larger amount of experimental data (Equation 56) (Zeng et al., 1998). 

To understand the etiology of hypoglycemia in the newborn, it is first necessary to know the principles of fetal metabolism that form the basis for newborn physiology and pathology. A unique characteristic of the fetus is the need for the continual provision of substrates across the maternal and placental circulations for growth and energy. A second unique characteristic of the fetus is its biochemical development so that it no longer needs this constant substrate supply (i.e., is capable of independent existence) at birth. 

Several fundamental features of polysaccharide biosynthesis are apparently present in all microbes. However, the fate of a substrate supplied to an exopolysaccharide-producing, microbial cell depends on the microbial species chosen. Although studies have been made with... 

When mitochondria are isolated and tested in media which only contain osmotic support (sucrose or KCl) and a buffer (and Mg, Pj and EDTA, if necessary), they respire rapidly on substrates such as succinate or glycerol-3-phosphate (citrate, 2-oxoglutarate and malate are poor substrates in brown fat mitochondria from most species, as the substrate permeases are poorly developed [16]). This rapid respiration is seen in Fig. 10.2. This observation was initially made even before the thermogenic function of brown adipose tissue was known [17]. When R. Em. Smith had established that heat production was the function of the tissue [18], an intrinsic uncoupled state of the mitochondria [19,20] could be understood as the means of heat production, the intensity of which would be limited only by substrate supply [21]. However, Horwitz et al. [21a] found that addition of the artificial uncoupler DNP could potentiate the respiration of the tissue, and the conclusion had to be that the mitochondria — although uncoupled when isolated — were coupled in situ. 

Biochemical pathway synthesis is the construction of consistent sets of enzyme-catalyzed bioreactions meeting certain specifications. One seeks to construct pathways which produce certain target bioproducts, under partial constraints on the available substrates (reactants), allowed byproducts, desired yield, productivity, etc. The pathway must include all reactions needed to convert initial substrates supplied to the bioprocess into final... 

In traditional CVD, thermal energy is used to activate the reaction in other words, a heated substrate supplies the energy necessary for the reaction to proceed at a given temperature. Sometimes the reaction temperature required for a sufficient growth rate is so high that there are side reactions, decomposition of the deposit or deleterious effects on the substrate. In such a case, to induce the reaction to occur at lower growth... 

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