Enzyme enhancement ratio

A log-log plot using K Km, /ccat and Acuncat data from the 18 separate cases of antibody catalysis exhibited a linear, albeit scattered, correlation over four orders of magnitude and with a gradient of 0.86 (Fig. 16).4 Considering the assumptions made, this value is sufficiently close to unity to suggest that the antibodies do stabilize the transition state for their respective reactions. However, even the highest A cat/A uncat value of 106 in this series (Tramontano et al., 1988) barely compares with enhancement ratios seen for weaker enzyme catalysts (Lienhard, 1973). 

One of the first enantiofacially selective processes catalyzed by an antibody involved the hydrolysis of enol esters [15]. Hapten 4 was used to elicit antibodies for the hydrolysis of enol ester 5 (Scheme 2). This reaction proceeds via a putative enolate intermediate 6 and the key asymmetric induction step involves antibody-catalyzed enantiofacial protonation of one of the prochiral faces of 6. Antibody 27B5 catalyzes the hydrolysis of the enol ester 5 with a turnover number k apO.Ol min corresponding to an enhancement ratio (ER), k j/non-cata-lyzed rate (kuncat) provides an optically enriched mixture of the R-ke-tone product 7 (42% ee). Although the asymmetric induction is lower than that achievable by natural enzymes for certain substrates [ 16], it was a successful demonstration, at entry level, for catalytic antibodies and asymmetric induction. 

To compare the catalytic efficiency of catalysts, it is helpful to compare the enhancement ratios (E.R.). E.R. is calculated by dividing the kcat by the kuncat (the rate constant for the uncatalyzed reaction). Enormous rate enhancements are achieved by enzymes. For example, hydrolytic enzymes often exhibit rate enhancements of 10 -10 2 compared with the spontaneous water-catalyzed or the acid/base-catalyzed reaction at about neutral pH. e For purposes of comparison, the kcat, kuncat, and E.R. values for two hydrolytic abzymes, as well as CCMP fluorohydrolase chromatographed on G-15 Sephadex gel is presented in Table 3. The fluorohydrolase, chromatographed on G-15 Sephadex, has an E.R. four times that of the two abzymes. In addition, the enhancement ratios of natural DFPases from various sources as well as CCMP fluorohydrolase are presented in Table 4. In all cases, the initial E.R. (before any purification) is higher for semisynthetic fluorohydrolases than for any of the natural unpurified DFPases. 

Semisynthetic fluorohydrolase has activity comparable to the naturally occurring DFPases and does not require a divalent cation as does the "Mazur-type" enzyme. It operates over a pH range from 6.5 to 8.0 with the optimum at approximately 7.5. A comparison of natural and semisynthetic fluorohydrolase activity is shown in Table 4. An examination of the enhancement ratio (2.2 x 10 ) shows that the CCMP fluorohydrolase is a remarkably good catalyst. If the crosslinking reaction is further optimized to increase the yield of the dimer along with further purification steps, a stable highly efficient semisynthetic fluorohydrolase should be achieved. 

The kinetic scheme is analogous to the Michaelis-Menten scheme for enzyme catalysis. The solvent-dependence of the rate-enhancement ratio can be explained in terms of different values for the initial interaction between substrate and micelle (Mic) measured by the partition coefficient K. The full scheme for a transformation of substrate (S) to product (P) is ... 

Enhanced thermal stability enlarges the areas of application of protein films. In particular it might be possible to improve the yield of reactors in biotechnological processes based on enzymatic catalysis, by increasing the temperature of the reaction and using enzymes deposited by the LB technique. Nevertheless, a major technical difficulty is that enzyme films must be deposited on suitable supports, such as small spheres, in order to increase the number of enzyme molecules involved in the process, thus providing a better performance of the reactor. An increased surface-to-volume ratio in the case of spheres will increase the number of enzyme molecules in a fixed reactor volume. Moreover, since the major part of known enzymatic reactions is carried out in liquid phase, protein molecules must be attached chemically to the sphere surface in order to prevent their detachment during operation. 

In the reaction, it was essential to use an IL as a co-solvent. Lozano, Iborra and co-workers recently reported an interesting stabilizing effect of two types of water-immiscible ILs ([emim][TFSI] and [BuMe3N][TFSI]) for CAL-B-catalyzed transesterification of vinyl butyrate. The synthetic activity and the stability of the enzyme in these IL solvent systems were markedly enhanced as compared to those in hexane. CAL-B maintained its activity higher than 75% after 4 days of incubation in [emim][TFSI] solvent, while it showed an activity of only 25% when incubated in both water and hexane media at 50°C. Comparison of the ratio of a-helix and (3-sheet by CD spectra showed the activity was closely related with a-helix content which reduced to 31% immediately after lipase was added to hexane and had reached only 2% after 4 days in hexane. On the contrary, no significant reduction of a-helix content was... 

When Rhizopus sp. 26R was cultivated in the solid substrates without addition of rice bran but composed of only wheat bran and rice husk at the ratio of 18 2. The pectinase activity from the culture was approx. 25-35 unit/ml within 2 days and the production remained constant for 4 days (Figure 3). One gram of raw starch from cassava tuber, 1 g of pectin or 0.5 g of yeast extract was added to the solid substrates in order to induce higher activity of the enzsrme. The results showed that either 1 g raw cassava starch or 1 g pectin that was added to the 20 g solid substrates increased the enzyme activity to 1.7 and 2.4 times, respectively (Figure 3). The production of pectinase in soHd substrates with wheat bran and rice husk could be enhanced with the addition of raw cassava starch and pectin. 

Miller and Wolfenden, 2002). This latter ratio is the inverse of the rate enhancement achieved by the enzyme. In other words, the enzyme active site will have greater affinity for the transition state structure than for the ground state substrate structure, by an amount equivalent to the fold rate enhancement of the enzyme (rearranging, we can calculate KJX = Ksik Jk, )). Table 2.2 provides some examples of enzymatic rate enhancements and the calculated values of the dissociation constant for the /A binary complex (Wolfenden, 1999). 

To date, there have only been a limited number of studies directly examining PKC in bipolar disorders [77], Although undoubtedly an oversimplification, particulate (membrane) PKC is sometimes viewed as the more active form of PKC, and thus an examination of the subcellular partitioning of this enzyme can be used as an index of the degree of activation. Friedman etal. [78] investigated PKC activity and PKC translocation in response to serotonin in platelets obtained from bipolar-disorder patients before and during lithium treatment. They reported that the ratios of platelet-membrane-bound to cytosolic PKC activities were elevated in the manic patients. In addition, serotonin-elicited platelet PKC translocation was found to be enhanced in those patients. With respect to brain tissue, Wang and Friedman [74] measured PKC isozyme levels, activity and translocation in postmortem brain tissue from patients with bipolar disorder, and reported increased PKC activity and translocation in the brains of bipolar patients compared with controls, effects which were accompanied by elevated levels of selected PKC isozymes in cortices of bipolar disorder patients. 

The higher surface area of CNTs can support a much higher density of enzymes than previous approaches such as thin films. Their high aspect ratio aids in the retention of enzyme-CNT conjugates in the matrix. CNTs also enhance the stability of adsorbed proteins relative to micro- or macro-scale supports, thereby helping to preserve or enhance enzyme bioactivity in the nanocomposites (Wang,... 

Willeman et al. [26] modeled the enzyme-catalyzed cyanohydrin synthesis in a stirred batch tank reactor. Assumption of a mass transfer limitation (Figure 9.3b) is made, which results in a low concentration of substrate in the aqueous phase, thus suppressing the non-enzymatic reaction. In a well-stirred biphasic system the enzyme concentration was varied, keeping the phase ratio constant A maximum rate of conversion is reached at the concentration where mass transfer of the substrate becomes limiting. Further increase of enzyme concentration does not enhance the reaction rate [27]. The different results achieved by the two groups are explained by the different process strategies. No mass transfer limitation could be detected by Hickel et al. because the stirring rate in the aqueous phase was not varied [26]. 

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