Esterase reactivators

Another possibility to treat a poisoning with esterase inhibitors of the organophosphorous type are the so called esterase reactivators compounds with an oxime structure like obidoxime and prali-doxime. The oxime moiety has a very high affinity for the phosphorous atom and can thereby under certain circumstances hydrolyze the otherwise stable organophosphorous-enzyme complex. 

Site-specific delivery of the acetylcholine-esterase reactivator 2-pam to the brain... 

B Oxidative bioactivation of losartan C Methyienedioxy derivatives as bioprecursors of catechols D Site-specific delivery of the acetyl-choline-esterase reactivator 2-PAM to the brain... 

The decomposition process of bispyridinium aldoximes TMB-4, by acetylcholine esterase reactivators, were observed in D2O solutions of different pD values and various temperatures [35]. Whereas the aldoximes turned out to be rather stable, corresponding ether and cyano derivatives were found to convert to the pyridone in alkaline medium at high temperatures. 

Immobilization. The fixing property of PEIs has previously been discussed. Another appHcation of this property is enzyme immobilization (419). Enzymes can be bound by reactive compounds, eg, isothiocyanate (420) to the PEI skeleton, or immobilized on soHd supports, eg, cotton by adhesion with the aid of PEIs. In every case, fixing considerably simplifies the performance of enzyme-catalyzed reactions, thus faciHtating preparative work. This technique has been appHed to glutaraldehyde-sensitive enzymes (421), a-glucose transferase (422), and pectin lyase, pectin esterase, and endopolygalacturonase (423). 

This process of aging is believed to be critical in the development of delayed neuropathy, after NTE has been phosphorylated by an OP (see Chapter 10, Section 10.2.4). It is believed that most, if not all, of the B-esterases are sensitive to inhibition by OPs because they, too, have reactive serine at their active sites. It is important to emphasize that the interaction shown in Fignre 2.11 occurs with OPs that contain an oxon group. Phosphorothionates, which contain instead a thion group, do not readily interact in this way. Many OP insecticides are phosphorothionates, but these need to be converted to phosphate (oxon) forms by oxidative desulfuration before inhibition of acetylcholinesterase can proceed to any significant extent (see Section 2.3.2.2). 

The primary site of action of OPs is AChE, with which they interact as suicide substrates (see also Section 10.2.2 and Chapter 2, Figure 2.9). Similar to other B-type esterases, AChE has a reactive serine residue located at its active site, and the serine hydroxyl is phosphorylated by organophosphates. Phosphorylation causes loss of AChE activity and, at best, the phosphorylated enzyme reactivates only slowly. The rate of reactivation of the phosphorylated enzyme depends on the nature of the X groups, being relatively rapid with methoxy groups (tso 1-2 h), but slower with larger... 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

By use of model substrates and inhibitor studies, an esterase that is reactive in unbuffered sea water as well as in the disrupted algal tissue from C. taxifolia was identified which mediates cleavage of the acetyl residues of caulerpenyne (54) [121]. After complete deacetylation, oxytoxin 2 (64) appears as an unstable end-product. Due to the lack of an appropriate assay procedure for labile metabo-... 

Another reactive site, called the T-site, makes a modest contribution to the overall hydrolytic activity of the protein (ca. 11%), and a lysine residue has been suggested as the catalyst. The position of the T-site might be in the subdomain IIA of HSA (Fig. 3.17), since there is evidence that Lys220 in sub-domain IIA could belong to an esterase site [119][120],... 

It is important to note that acetylsalicylic acid and some 4-nitrophenyl esters are quite reactive species that easily acylate nucleophiles. With such compounds, albumin indeed behaves as a catalyst, but it is simultaneously a target, and the term esterase-like activity can only be understood with this restriction in mind. 

Whereas the above evidence clearly points to a catalytic activity of serum albumin, it does not exclude an activity toward less-reactive substrates due to contamination of some HSA preparations. Indeed, the hypothesis of a contamination by plasma cholinesterase (EC 3.1.1.8) has been raised [126][127]. The efficient hydrolysis of nicotinate esters by HSA (see Chapt. 8) [128][129] could be due to contamination by cholinesterase in samples of a commercially available, essentially fatty acid free albumin. Support for this hypothesis was obtained when HSA contaminated with cholinesterase was resolved into two peaks by affinity chromatography, and the esterase activity toward nicotinate esters was found exclusively in the cholinesterase fraction [130],... 

Y. Kurono, H. Yamada, K. Ikeda, Effects of Drug Binding on the Esterase-Like Activity of Human Serum Albumin. V Reactive Site towards Substituted Aspirins , Chem. Pharm. Bull. 1982, 30, 296 - 301. 

Thioesters play a paramount biochemical role in the metabolism of fatty acids and lipids. Indeed, fatty acyl-coenzyme A thioesters are pivotal in fatty acid anabolism and catabolism, in protein acylation, and in the synthesis of triacylglycerols, phospholipids and cholesterol esters [145], It is in these reactions that the peculiar reactivity of thioesters is of such significance. Many hydrolases, and mainly mitochondrial thiolester hydrolases (EC 3.1.2), are able to cleave thioesters. In addition, cholinesterases and carboxylesterases show some activity, but this is not a constant property of these enzymes since, for example, carboxylesterases from human monocytes were found to be inactive toward some endogenous thioesters [35] [146], In contrast, allococaine benzoyl thioester was found to be a good substrate of pig liver esterase, human and mouse butyrylcholinesterase, and mouse acetylcholinesterase [147],... 

Selected entries from Methods in Enzymology [vol, page(s)] Sulfonylation reaction, 11, 706 reaction kinetics, 11, 707 second-order rate constants for inactivation of chymotrypsin, trypsin, and acetylcholine esterase by PMSE and related sulfonylat-ing agents, 11, 707 reactivation of PMS-chymotrypsin, 11, 710 as inhibitor [of calcium-activated factor, 80, 674 of cathepsin G, 80, 565 of crayfish trypsin, 80, 639 of elastase, 80, 587 of pro-lylcarboxypeptidase, 80, 465 of protease Re, 80, 691 of protease So, 80, 695 of protein C, 80, 329] proteolysis, 76, 7. 

In connection with research on oximes as reactivators of phosphorylated acetylcholine esterase, a number of studies have shown that introduction of cationic micelles such... 

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