Enzymes enzyme elimination

Optimization of Substrate Concentrations. Computer analyses of enzyme kinetics may be very useful for the calculation of enzyme constants, eliminating the tediim associated with manual calculations. Recently, computer models for optimizing reagent concentrations have been described but these models require so many experimental points that the model rests on the experimental data rather than having predictive usefulness (31). 

The acyl-enzyme can eliminate the 4-chlorine atom to generate this reactive intermediate that can then react with a nearby nucleophile such as His57 to give an alkylated acyl-enzyme derivative in which the inhibitor moiety is bound to the enzyme by two covalent bonds (Scheme 11.5). Inhibition is irreversible.59 The mechanism has been confirmed by X-ray structural analysis of protease-isocoumarin complexes. There is a cross-link between the inhibitor and the Serl95 and His57 residues of PPE.60 Human leukocyte elastase is also very efficiently inactivated.61... 

Another report describing an approach to achieve alleviation of sulfur repression came from the Matsui research group. The dsz genes were cloned into a strain Rhodococcus sp. strain T09 under the promoter rrn of the strain T09 using a Rhodococcus-E. coli shuttle vector [214,215], This resulted in a strain which desulfurized DBT to 2-HBP in presence of sulfate, cysteine, or methionine. Similar approach was also used by Kurane to construct a gene expressing dszA-D enzymes, which eliminate the sulfate inhibition effects [216],... 

Worthy of note in this reaction is that citrate displays prochirality (see Section 3.4.7). The methylene carbons may be considered prochiral, in that enzymic elimination of a proton is likely to be entirely stereospecific. In addition, the apparently equivalent side-chains on the central carbon are also prochiral and going to be positioned quite differently on the enzyme. This means that only one of these side-chains is involved in the dehydration-rehydration... 

In the case of 5-fluoro-deoxycytidine (FdC) an methylated adduct (Illb) is also formed, from which (again due to substitution of the a-proton by the fluorine) no liberation of the enzyme by elimination is possible [74], Zebularine is a riboside prodrug like azadtidine that is also incorporated in both RNA and DNA. It is somewhat different, though, as the covalent enzyme addud (Ib) is formed but methylation does not occur and is not necessary for inhibition. Although elimination of the enzyme should be possible, a stable intermediate is formed [35] (Figure 8.9). 

Ibuprofen is a common pain reliever that (even in low dosages) used to cause a false THC positive on the EMIT test. The EMIT has been changed to use a different enzyme to eliminate false positives due to Ibuprofen. Ibuprofen in very high doses will still interfere with both the EMIT and the GC/MS. There is some conflicting data here because some sources say that the GC/MS tests can distinguish between Ibuprofen and THC (as well as other over-the-counter drugs). 

Pharmacohinetics Extensively distributed after PO administration. Protein binding 93%-97%. Rapidly and extensively metabolized by multiple enzymes. Primarily eliminated in urine with a lesser amount excreted in feces. Half-life 30-40 hr. 

Figure 10.2 One of the procedures for entrapping an enzyme, E, (or any other solute) inside liposomes. The non-entrapped enzyme is eliminated by size exclusion chromatography, then the substrate (ADP in this case) is left to permeate throughout, the ADP excess is again eliminated chromatographically, and the reaction kinetics - due to the internalized enzyme reaction - measured. (From Walde et al., 1994b.)...

The mechanisms that underlie ethanol s teratogenic effects are unknown. Ethanol rapidly crosses the placenta and reaches concentrations in the fetus that are similar to those in maternal blood. The fetal liver has little or no alcohol dehydrogenase activity, so the fetus must rely on maternal and placental enzymes for elimination of alcohol. 

Although the role of lipid composition in membrane function is not entirely understood, changes in composition can produce dramatic effects. Researchers have isolated fruit flies with mutations in the gene that encodes ethanolamine kinase (analogous to choline kinase Fig. 21-28). Lack of this enzyme eliminates one pathway for phosphatidylethanolamine synthesis, thereby reducing the amount of this lipid in cellular membranes. Flies with this mutation—those with the genotype easily shocked—exhibit transient paralysis following electrical stimulation or mechanical shock that would not affect wild-type flies. 

The mercapturic acids and related compounds can then be exported from cells by an ATP-dependent export pump. Glutathione is a coenzyme for glyoxalase (Eq. 13-33), maleylacetoacetate isomerase (Eq. 13-20), and DDT dehydrochlorinase. The latter enzyme catalyzes elimination of HC1 from molecules of the insecticide and is especially active in DDT-resistant flies.3 Glutathione is said to be the specific factor eliciting the feeding reaction of Hydra that is, the release of glutathione from injured cells causes the little animal to engulf food. 

Gal-(1— 3)-D-GalNAc. By using 0.7 U of STB, as a soluble preparation readily obtained from 300 g of porcine liver, the sialylation of /J-D-Gal-(1 — 3)-d-G1cNAc was performed on a one-mmol scale and sialylated trisaccharide 65 was obtained in 21 % isolated yield. In this respect, the purification of reaction mixtures is still troublesome, especially because of the presence of Triton X-100 from our experience, the use of immobilized enzymes, eliminating the need for detergent, greatly facilitates the purification procedure. 

The mechanism responsible for improved detection is thought to be better accessibility of glycotopes to the antibody glycotopes usually are masked by unrelated large oligosaccharides. The enzyme treatment eliminates steric hindrance by these oligosaccharides. The mechanism of antigen retrieval essentially is based on the depolymerization of... 

Experimental pharmacological investigations into selected acyl enzymes have shown that, besides the depot effect of the modified enzymes, their elimination characteristics changed as did, in some cases, their specific effect, m particular, as for as fibrinolytic enzymes are concerned, acylation could be shown to modify significantly the clearance of these enzymes. The prolonged circulation of... 

It is known that p-lactamase catalyzes the rapid hydrolysis of the p-lactam ring of penicillins and cepharosporines. The hydrolytic activity of these enzymes eliminates the bacteriocidal action of many p-lactam antibiotics and makes the organism resistant to these molecules. For this reason, the p-lactamase inhibitors have long been regarded as promising targets from a medicinal viewpoint. A comparison between the kinetic characteristics of p-lactamase and penicillin-sensitive enzymes (carboxy-peptidase and transpeptidase) is of interest in this respect. p-Lactamases very efficiently hydrolyze p-lactam in contrast to penicillin-sensitive enzymes [high /e4 in Eq. (9)]. 

Bjorkhem, I., Andersson, O., Diczfalusy, U., Sevastik, B., Xiu, R.-J., Duan, C., Lund, E.G. 1994. Atherosclerosis and sterol 27-hydroxylase evidence for a role of this enzyme in elimination of cholesterol from human macrophages. Proc. Natl. Acad Sci. USA 91, 8592-8596. 

Reaction Optimization. The use of enzymes in organic media is often not a straightforward endeavor. Numerous conditions must be satisfied in order to obtain optimal catalysis including the maintenance of the proper ionogenic state of the enzyme and elimination of diffusional limitations (via proper biocatalyst preparation). 

A process was developed in Germany using the enzyme immobilized on 350 A pore diameter Eupergit C for production of 5 -ribonucleo-tides from crude nucleic acid mixtures containing both RNA and DNA (42). Apparently the larger DNA is excluded from the pore volume while the smaller RNA has access to the enzyme, thus eliminating the requirement for a difficult separation of RNA from DNA. Using a substrate stream of crude nucleic acid adjusted to 0.1 mM ZnSO at pH 5.0 and 60°C, a 10-inch x 25-inch fixed-bed bioreactor produced 10... 

The 1,2-migration of amino groups in /3-aminoalkyl radicals such as 24 has also been of interest because of the involvement of these species in the enzyme-catalyzed elimination of ammonia from 1,2-amino alcohols.47-50 These studies have also been reviewed recently by Radom et al45... 

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