Enzyme conversion rate

An alkaline pH (- pH 11) is desirable in order to achieve high conversion rates increase solubility of L-phenylalanine inhibit enzymes catalysing degradation of L-phenylalanine and formation of byproducts reduce inhibition of the reaction by the keto form of phenylpyruvic arid. 

The E. coli enzyme accepts substitution on either cosubstrate propanal, acetone or 1-fluoro-2-propanone can replace the donor and a variety of aldehydes can replace the acceptor moiety 3. Shortcomings are the relatively low conversion rates obtained for any substrate analog and the as yet unidentified level of relative stereocontrol induced upon substitution at the nucleophilic carbon. 

The 2-ethoxyethanol was a by-product, as shown in Figure 5.13. The formation rate of 2-ethoxyethanol was the same as the conversion rate of the (S)- or (R)-ibuprofen ester one mole of 2-ethoxyethanol was formed when one mole of ester was catalysed. A known concentration of 2-ethoxyethanol was added in the organic phase before the start of the reaction for product inhibition. The plots of the kinetics for the free lipase system are presented in Figure 5.17 and immobilised enzyme (EMR) in Figure 5.18, respectively. The Kw value was 337.94 mmoFl 1 for the free lipase batch system and 354.20 mmoll 1 for immobilised... 

D-Xylulose 5-phosphate (ii-threo-2-pentulose 5-phosphate, XP) stands as an important metabolite of the pentose phosphate pathway, which plays a key fimction in the cell and provides intermediates for biosynthetic pathways. The starting compound of the pathway is glucose 6-phosphate, but XP can also be formed by direct phosphorylation of D-xylulose with li-xylulokinase. Tritsch et al. [114] developed a radiometric test system for the measurement of D-xylulose kinase (XK) activity in crude cell extracts. Aliquots were spotted onto silica plates and developed in n-propyl alcohol-ethyl acetate-water (6 1 3 (v/v) to separate o-xylose/o-xylulose from XP. Silica was scraped off and determined by liquid scintillation. The conversion rate of [ " C]o-xylose into [ " C]o-xylulose 5-phosphate was calculated. Some of the works devoted to the separation of components necessary while analyzing enzyme activity are presented in Table 9.8. 

At low temperatures, the nonenzymatic reaction is reduced to a larger extent than the enzymatic reaction. The mass transfer rate is reduced to a smaller extent. Mass transfer limitation is required for high enantiomeric excess and determines the conversion rate. Therefore, the volumetric productivity decreases at lower temperatures. The equilibrium constant is considerably higher at low temperatures, resulting in a higher extent of conversion or a lower HCN requirement. Both the volumetric productivity and the required enzyme concentration increase by increasing the reaction temperature and aqueous-phase volume while meeting the required conversion and enantiomeric excess [44]. The influence of the reaction medium (solvent and water activity) is much more difficult to rationalize and predict [45],... 

The tabulated data of initial rates and concentrations were obtained for enzyme conversion of a substrate at 37 C, pH 6.5. 

The most fundamental process dealing with the activation of C02 involves the hydration of C02 to produce bicarbonate and the reverse dehydration of bicarbonate to produce C02. These processes are of biological and environmental significance since they control the transport and equilibrium behavior of C02. The spontaneous hydration of C02 and dehydration of HCO3 are processes that are too slow and must therefore be catalyzed by metal complexes in order to expedite the overall conversion rate. In biological systems, a series of enzymes, the carbonic anhydrases, are the efficient catalysts and can accelerate the reactions by up to 7 orders of magnitude. The mechanism of this... 

With respect to an enzyme, the rate of substrate-to-product conversion catalyzed by an enzyme under a given set of conditions, either measured by the amount of substance (e.g., micromoles) converted per unit time or by concentration change (e.g., millimolarity) per unit time. See Specific Activity Turnover Number. 2. Referring to the measure of a property of a biomolecule, pharmaceutical, procedure, eta, with respect to the response that substance or procedure produces. 3. See Optical Activity. 4. The amount of radioactive substance (or number of atoms) that disintegrates per unit time. See Specific Activity. 5. A unitless thermodynamic parameter which is used in place of concentration to correct for nonideality of gases or of solutions. The absolute activity of a substance B, symbolized by Ab, is related to the chemical potential of B (symbolized by /jlb) by the relationship yu,B = RTln Ab where R is the universal gas constant and Tis the absolute temperature. The ratio of the absolute activity of some substance B to some absolute activity for some reference state, A , is referred to as the relative activity (usually simply called activity ). The relative activity is symbolized by a and is defined by the relationship b = Ab/A = If... 

A term usually synonymous to rate of reaction in the field of enzyme kinetics. Rate is the preferred terminology. See Rate of Reaction Rate of Conversion... 

A further requirement for the development of a multi-enzyme oxidizing process would be the determination of the kinetic parameters of the enzymes and hence development of a model of the intended reaction system in terms of the relative productivities of the enzymes with respect to substrate conversion rates as well as electron transfer stoichiometry. 

Figu re 3.3 Conceptual process model for application of a coupled tyrosinase-laccase reaction converting tyrosol. Immobilized enzymes are first characterized with respect to substrate conversion rates, using tyrosol and hydroxytyrosol as substrates for tyrosinase and laccase, respectively. One hundred percent conversion can be achieved in Reactor 1 by use of sufficient tyrosinase... 

In the case of the (1 )-configured olefinic ketones high conversion rates and enantiomeric excesses were achieved on the analytical and on the semi-preparative scale. With TBADH, which requires a slightly higher reaction temperature, decomposition of the halogenated substrates was observed. In the case of CPCR, which was used as a partially purified enzyme preparation from the parental strain, the formation of up to 50% of the fully saturated alcohols was observed (Scheme 2.2.7.18). Substrate (l )-33 could be converted into enantiopure (S)- and (R)- E)-32, respectively, by recLBADH- and HLADH/CPCR-catalyzed reaction. 

The chromatogram and bar graph show results of a study of aspirin metabolism in a rat. Aspirin is converted into salicylic acid by enzymes in the bloodstream. To measure the conversion rate, aspirin was injected into a rat and dialysate from a microdialysis probe in a vein of the rat was monitored by liquid chromatography. If you simply withdrew blood for analysis, aspirin would continue to be metabolized by enzymes in the blood. Microdialysis separates the small aspirin molecule from large enzyme molecules. 

A salient shortcoming of the catalyst is the relatively low conversion rate obtained with any of the substrate analogs tested ( < 1 %) which in practice must be compensated by utilization of large amounts of enzyme and long reaction times. Thus, in reactions leading to thermodynamically unfavorable products it has been observed under equilibrating conditions that—in common with results discussed above for other aldolases — additions do not proceed fully stereospecifically at the reaction center [369],... 

The simplest enzymatic system is the conversion of a single substrate to a single product. Even this straightforward case involves a minimum of three steps binding of the substrate by the enzyme, conversion of the substrate to the product, and release of the product by the enzyme (Scheme 4.6). Each step has its own forward and reverse rate constant. Based on the induced fit hypothesis, the binding step alone can involve multiple distinct steps. The substrate-to-product reaction is also typically a multistep reaction. Kinetically, the most important step is the rate-determining step, which limits the rate of conversion. 

On the other hand, no significant difference in total sugar yield was observed between the 0.5- and 2-g loading for either two- or one-enzyme preparations, but the conversion rate was faster when the higher loading was used. 

Many of the equations employed in unstructured and non-segregated models derive from those of enzymatic kinetics (Sinclair and Kristiansen, 1987 Nielsen and Nikolajsen, 1988). Cells are considered as chemical reactors that support thousands of complex reactions catalyzed by enzymes that allow the conversion of substrates into secreted products. The equation formulated by Michaelis and Menten represents the enzymatic conversion rate of a unique substrate into one product (Equation 14). 

Fig. 3.4 The glycolytic pathway produces NADH which under regular conditions is oxidized to NAD+ while reducing acetaldehyde (ACA) to ethanol (EtOH), thereby in turn reducing NAD+ in order to keep hexose catabolism running. The actual cytosolic NADH concentration is determined by the respective conversion rates of the enzymes involved in the oxidation and regeneration of the compound. If these enzymes convert additional non-natural substrates (xenobiotics, i.e. drugs), the conversion rate changes. As a consequence, the cytosolic NADH concentration differs from the natural condition. Furthermore, if a xenobiotic acts as an enzyme inhibitor, e.g. for ADH, then NAD+ regeneration is substantially affected, which eventually results in altered cytosolic NADH concentration. Therefore the presence of a xenobiotic in the cell is conceivably a perturbation factor. Under the conditions where glycolytic oscillations...

Variables in alcoholic fermentation, the yeast-enzyme conversion of grape sugar to ethanol and carbon dioxide, have a major impact on the character, composition, and quality of North Coast white table wines. Type of yeast, juice solids content, juice S02 content, juice protein content, fermentation temperature, and fermentation rate are factors the enologist may consider and control. 

Goswami and Rosenberg have suggested that liver and kidney microsomes contain in addition to the type I deiodinase multiple low-Mm enzymes for the ORD of T4 and rT3 that differ from the type II enzyme [60,64,65]. This was mainly based on different susceptibilities to iopanoic acid and PTU if reactions were carried out at low substrate concentrations in the presence of various cofactors, i.e., DTT, GSH, glutaredoxin and thioredoxin [60,64,65]. It was even reported that the deiodinase activity stimulated by the thioredoxin system accepted rT3 but not T4 as substrate [64]. The uncertainty in the estimation of the low conversion rates in the nM substrate range which are not accounted for by residual activity of the type I deiodinase, however, questions the validity of the above conclusions. The possible exist-... 

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