Enzymes enzyme efficiency

In contrast to SDS, CTAB and C12E7, CufDSjz micelles catalyse the Diels-Alder reaction between 1 and 2 with enzyme-like efficiency, leading to rate enhancements up to 1.8-10 compared to the reaction in acetonitrile. This results primarily from the essentially complete complexation off to the copper ions at the micellar surface. Comparison of the partition coefficients of 2 over the water phase and the micellar pseudophase, as derived from kinetic analysis using the pseudophase model, reveals a higher affinity of 2 for Cu(DS)2 than for SDS and CTAB. The inhibitory effect resulting from spatial separation of la-g and 2 is likely to be at least less pronoimced for Cu(DS)2 than for the other surfactants. 

Compared to penicillins, cephalosporins are generally effective against a broader range of organisms and are more resistant to /3-lactamases. /3-Lactamases are bacterial enzymes that efficiently hydrolyze /3-lactam antibiotics to inactive species in which the /3-lactam bond has been cleaved. Cephalothin was the first cephalosporin to be marketed and continues... 

But k must always be greater than or equal to k h / (A i + kf). That is, the reaction can go no faster than the rate at which E and S come together. Thus, k sets the upper limit for A ,. In other words, the catalytic effieiency of an enzyme cannot exceed the diffusion-eontroUed rate of combination of E and S to form ES. In HgO, the rate constant for such diffusion is approximately (P/M - sec. Those enzymes that are most efficient in their catalysis have A , ratios approaching this value. Their catalytic velocity is limited only by the rate at which they encounter S enzymes this efficient have achieved so-called catalytic perfection. All E and S encounters lead to reaction because such catalytically perfect enzymes can channel S to the active site, regardless of where S hits E. Table 14.5 lists the kinetic parameters of several enzymes in this category. Note that and A , both show a substantial range of variation in this table, even though their ratio falls around 10 /M sec. 

Loss of enzyme efficiency was due to short and long-term PG distribution between the different products (Fig. 2). 

Enzymes to degrade crosslinked hydroxypropylated starch derivative and xanthan gum polymer systems are available [158,1246]. Specific enzymes are efficient in reducing the near wellbore damage induced by the starch polymer to eventually return permeabilities to the range of 80% to 98% without the use of acid systems. 

Enzymes are efficient catalysts for cathodic and anodic reactions relevant to fuel cell electrocatalysis in terms of overpotential, active site activity, and substrate/reaction specificity. This means that design constraints (e.g., fuel containment and anode-cathode separation) are relaxed, and very simple devices that may take up ambient fuel or oxidant from their environment are possible. While operation is generally confined to conditions close to ambient temperature, pressure, and pH, and power densities over about 10 mW cm are rarely achieved, enzyme fuel cells may be particularly useM in niche environments, for example scavenging trace H2 released into air, or sugar and O2 from blood. Thus, trace or unusual fuels become viable for energy production. 

The studies described above show that a quinone methide or its aza-analogue quinonimine methide incorporated as a latent electrophilic species into a cyclic lactone or lactam precursor can modify a second nucleophilic residue within the enzyme active site after formation of the acyl-enzyme. Very efficient suicide... 

Although the size distribution of fragments from heparinase (and hep-aranase) digests reflects the relative content of regular sequences 5 in different heparin preparations and fractions, these sequences may be quantitated only when the enzyme efficiency is high, and products are... 

The Influence of Environmental Factors on Enzyme Kinetics. Because enzymes are proteins, they are unusually sensitive to changes in their environment. This is true not only with regard to variations in inhibitor concentrations, but also with respect to variations in pH and temperature. Most enzymes are efficient catalysts only within relatively narrow ranges of pH and temperature. 

Chemists and biochemists have studied the complex enzyme nitrogenase for all of modem scientific times. Many models for the enzyme s efficient reduction and protonation of dinitrogen to the useful product ammonia have been put forward. Many different research groups have based these models on analytical and instmmental observations. Crystallization of the enzyme s subunits and subsequent X-ray crystallographic structures in the 1990s yielded an intimate portrait informing all aspects of research on nitrogenase. In spite of the many structural and analytical successes, aspects of the enzyme s structure and function remain controversial or unclear up to the present time. 

In contrast, antioxidant enzymes can efficiently counteract all UV-induced ROS (Aguilera et al. 2002). These enzymes are represented by superoxide dismutase (SOD), catalase and glutathione peroxidase as well as those involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, mono-dehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. One of the most important classes of antioxidant enzymes is the SOD family, which eliminate noxious superoxide radical anions. Different metalloforms of SOD exist (Fe, Mn, CuZn and Ni), which due to their intracellular localisation protect different cellular proteins (Lesser and Stochaj 1990). 

An example of esterase behaviour is provided by a catalytic antibody developed by Tramontano et al. (1988), using a phosphonate transition state analogue [53] as the hapten. The antibody cleaves the carboxylic ester [54, R = Me] with enzyme-like efficiency (kc/ku = 6.25 X 106 = 1.5 mM ... 

The cumulative evidence that each individual human being has a distinctive pattern of enzyme efficiences is hard to refute on any rational basis. Furthermore, inter-individual variations in enzyme efficiencies in normal individuals, insofar as they have been determined, are not of the order of 20 to 50 per cent, but are more often at least 3- or 4-fold. Differences of 10- to 50-fold ( ) have been observed in a substantial number of cases even when the number of normal individuals tested was small. 

A detailed understanding of the mechanism of enzyme catalysis and of the reasons for enzyme catalytic efficiency requires knowledge of the... 

In recent years attention has focused on the role of intrinsic binding energy and entropic factors as major contributors to enzyme catalytic efficiency (Page and Jencks, 197l Jencks, 1975,1981). The ribonuclease mechanism conforms to expectations based on these ideas. In particular, distortion occurs to raise the ground state of the substrate in the S complex, and the bound substrate interacts with the enzyme in a manner such that the enzyme becomes complementary to the transition state of the reaction during the catalytic cycle. 

The reasons for the increasing acceptance of enzymes as reagents rest on the advantages gained from utilizing them in organic synthesis Isolated or wholecell enzymes are efficient catalysts under mild conditions. Since enzymes are chiral materials, optically active molecules may be produced from prochiral or racemic substrates by catalytic asymmetric induction or kinetic resolution. Moreover, these biocatalysts may perform transformations, which are difficult to emulate by transition-metal catalysts, and they are environmentally more acceptable than metal complexes. 

Irradiation at >320 nm releases from the polymer, whether insoluble or water-soluble, free oligosaccharides in very high yields. A simple illustration of such a sequence carried out with either insoluble 2-aminoethyl-substituted poly(acrylamide) beads or with water-soluble, substituted poly(vinyl alcohol) is presented in Scheme 9 the isolated overall yield of lactose was 29.9% (soluble-polymer approach). The synthesis on light-sensitive polymers facilitates the isolation of products, which is important from the preparative point of view and as a tool for the study of enzymes, permitting efficient comparison of acceptor specificity and being capable of demonstrating de novo synthesis. 

In 1991 bile-acid secretion was shown to be energy driven by a 110-kDa glycoprotein that was dependent on ATP. This protein was subsequently characterised as liver ecto-ATPase by Sippel and co-workers. However, while further work with COS cells showed that expression of ecto-ATPase enhanced secretion of bile acids purified canalicular membranes lacking this enzyme efficiently exported bile acids showing that at least one other bile-acid transporter existed. ... 

Remarkably, incorporation of fluorinated amino acids into proteins can also be accomplished in vivo. This supposes that the fluorinated amino acid analogs are recognized by the appropriate amino acyl-tRNA synthetase enzyme with efficiency similar to that of the natural amino acid. The proliferase response elicited by a fluorinated analog (a trifluoroisoleucine derivative) of murine interleukin-2 produced in an appropriate Escherichia coli strain was nearly as high as that of the authentic cytokine, indicating folding into an authentic, native structure [84],... 

The tyrosine protein sulfotransferase preparations from Golgi-enriched membranes have been used for sulfation of synthetic mono- and multiple-tyrosine peptides related to known sulfation sites in proteins and peptides at analytical levels to establish the enzyme specificities.1f11-13] Preparative sulfations have not been carried out to date. A novel type of arylsulfotransferase produced by Eubacterium A-44 which is part of the human intestinal flora, has recently been discovered.1"1911111 This enzyme catalyzes the transfer of a sulfate group from phenolic sulfate, but not from 3 -phosphadenosine-5 -phosphasulfate, to other phenolic compounds. Using 4-nitrophenylsulfate as a donor substrate and tyrosine-containing peptides and proteins as acceptor substrates it catalyzes the specific sulfation of the tyrosine residues.11111-112 While this enzyme very efficiently sulfates tyrosine derivatives, the... 

Okahata, Y. and Mori, T. (1997) Lipid-coated enzymes as efficient catalysts in organic media. Trends Biotechnol., 15, 50-54. 

The concept of immobilizing enzymes and cells on a polymer scaffold has been studied for several decades in one form or another. The work was driven by the need to increase the half-lives of enzymes, which are notoriously short. Part of the problem is that enzymes at efficient concentrations degrade each other. Denaturation and poisoning are similarly detrimental to the life of an enzyme. It was hypothesized that some of these problems could be mitigated by attaching the enzyme to a substrate. Experience has shown this is an effective way to improve the efficiency of what can be very expensive biological catalysts. 

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