Substrate concentration, effects enzymes

At what substrate concentration are enzymes most effective and respond best to the needs of the cells, and why ... 

Substrate Concentration Effects on the Reaction Rate, Enzyme Stability, Substrate Conversion 279... 

During the course of our research on nitrile hydratase- and amidase-catalyzed reactions we had to deal with different aspects of substrate concentration effects on the enzyme kinetics and all were suitably investigated making use of a CSMR, as shown by the following case studies. 

The Effect of Substrate Concentration on Enzyme-Catalyzed Reactions... 

Explain the effect of substrate concentration on enzyme-catalyzed reactions. 

The effect of substrate concentration on enzyme kinetics was first proposed by Henri at the beginning of the XX century. Making an analogy with reversible chemical reactions between two substrates, Henri proposed that conversion of substrate into product involved a reversible reaction between enzyme and substrate to form an active intermediate that brakes down delivering the product. These ideas were taken a few years later by Michaelis and Menten (1913) who proposed the first formal hypothesis for enzyme catalysis based on two sequential steps, as suggested by Henri in the first step the substrate is captured in the active site of the enzyme, while in the second step the amino acid residues at that site chemically process the substrate to... 

The kinetic expression for observed isotope effects is the ratio of both entire rate equations describing the disappearance of hydrogen and deuterium substrates. The isotopically sensitive step appears in multiple terms and cannot be factored out. In order to achieve factoring and subsequent simplification to useful kinetic equations, it is necessary to examine the Umits of rate equations at low and high substrate concentrations, where enzyme reactions approach first-order and zero-oider kinetics, respectively. To understand this, we must consider how isotope effects in bisubstrate reactions are measured. 

Figure 11.13 Effect of increasing substrate concentration on enzyme activity. 

No enzymatic side effects are observed and substrate concentrations up to 20% by weight can be used without affecting the enzyme activity. The biocatalyst is used in soluble form in a batch wise process, thus poorly soluble amino adds can be resolved without technical difficulties. Re-use of the biocatalyst is in prindple possible. 

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

The co-administration of drugs which induce the metabolic enzymes in the liver or small intestine can reduce the plasma concentrations of drugs which are substrates of the enzyme, leading to reduced drug effects. For example, the plasma concentrations of many drugs which are substrates of the enzyme CYP3A4, such as cyclosporine, are decreased by coadministration of rifampicin, which is an inducer of CYP3A4. 

Figure 4. The citrate cycle. There is complete oxidation of one molecule of acetyl-CoA for each turn of the cycle CH3COSC0A + 2O2 - 2CO2 + H2O + CoASH. The rate of the citrate cycle is determined by many factors including the ADP/ATP ratio, NAD7NADH ratio, and substrate concentrations. During muscle contraction, Ca is released from cellular stores (mainly the sarcoplasmic reticulum) and then taken up in part by the mitochondria (see Table 2). Ca " activates 2-oxoglutarate and isocitrate dehydrogenases (Brown, 1992). Succinate dehydrogenase may be effectively irreversible. Enzymes ...

Figure 8-3. Effect of substrate concentration on the initial velocity of an enzyme-catalyzed reaction.

A competitive inhibitor and substrate exert reciprocal effects on the concentration of the EI and ES complexes. Since binding substrate removes free enzyme available to combine with inhibitor, increasing the [S] decreases the concentration of the EI complex and raises the reaction velocity. The extent to which [S] must be increased to completely overcome the inhibition depends upon the concentration of inhibitor present, its affinity for the enzyme K-, and the of the enzyme for its substrate. 

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