Esterase modification

The differentiation of cells occurs concomitantly to modifications of wall components. The nature of the pectins of the walls changes under the action of enzymes, among which esterases, secreted between the apical meristematic cells and the more basal differentiated cells. The apposition of new layers of pectins with different compositions at the inner surface of the walls is another mechanism by which the cells adapt their immediate environment. Using the 2F4 antibody, we have observed, in plant suspensions as well as in tissues, a third mechanism involved in wall modification. Numerous invaginations of the... 

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... 

Modifications of the arylamino moiety profoundly influence the rate of hydrolysis. Thus, the hydrolysis of N- ace ty 1 -4-am i no be n zo i c acid was ca. 1000-fold slower than that of acetanilide [66]. Sorci and Macalady [67] investigated the influence of ring substitution on the hydrolysis of para-substituted acetanilides (4.104) in alkaline solution and in soil bacteria. No correlation was found between alkaline and biotic hydrolysis, which appeared to be controlled by different physicochemical properties. Bacterial hydrolysis was best correlated with the Van der Waals radius of the substituent, whereas chemical hydrolysis was correlated with the Hammett constant characterizing the electron-withdrawing capacity of the substituent. Other studies confirmed that a correspondence between bacterial and mammalian esterases... 

Due to the extreme variety of xylan structures, it is obvious that many kinds of enzymes are needed for their complete hydrolysis in nature. Xylanases (EC 3.2.1.8.) are the polysaccharide hydrolases responsible for the attack of the polymer backbone itself. The total hydrolysis or modification of heteroxylans requires in addition several different exo-glycosidases and esterases. The present knowledge of these enzymes is reviewed in this paper. 

Alisch M, Feuerhack A, MueUer H et al (2004) Biocatalytic modification of polyethylene terephthalate fibres by esterases from actinomycete isolates. Biocatal Biotrans 22 347-351... 

Matama T, Vaz F, Gubitz GM et al (2006) The effect of additives and mechanical agitation in surface modification of acrylic fibres by cutinase and esterase. Biotechnol J 1 842-849... 

The mechanisms of resistance fall into two main categories. Many insects produce an increased level of detoxifying enzymes, such as esterases, that modify the insecticides to inactive metabolites very rapidly. Such a system is seen in aphids that are resistant to OP insecticides. In other cases it is the target site that is modified such that the insecticide (the enzyme inhibitor) no longer binds to the target and is, therefore, ineffective. This has recently been shown to occur in some aphids that are resistant to OP insecticides but the classical example is knockdown resistance (kdr) and super-kdr to pyrethroid insecticides shown by many insects but particularly house flies Musca domes tied). This resistance is thought to result from a modification of... 

The role of certain residues in the enzyme mechanism has been confirmed by chemical modification studies, notably for tyrosine. 14 Modification of tyrosyl residues (for example acetylation or nitration) leads to loss of peptidase activity and enhancement of esterase activity. The presence of the inhibitor -phenylpropionate protects two tyrosine residues from acetylation. Those are Tyr-248 and probably Tyr-198, which is also in the general area of the active site. The modified apoenzyme has lower affinity for dipeptides, as might be expected from the loss of hydrogen bonding between Tyr-248 and the peptide NH group. 

Plettner E., DeSantis G., Stabile M. and Jones J. B. (1999) Modulation of esterase and amidase activity of subtilisin Bacillus lentus by chemical modification of cysteine mutants. J. Am. Chem. Soc. 121, 4977-4981. 

The greatly increased nucleophilicity of the catalytic serine distinguishes it from all other serine residues and makes it an ideal candidate for modification via activity-based probes [58]. Of the electrophilic probe types to profile serine hydrolases, the fluorophosphonate (FP)-based probes are the most extensively used and were first introduced by Cravatt and coworkers [38, 39]. FPs have been well-known inhibitors of serine hydrolases for over 80 years and were first applied as chemical weapons as potent acetylcholine esterase inhibitors. As FPs do not resemble a peptide or ester substrate, they are nonselective towards a particular serine hydrolase, thus allowing the entire family to be profiled. FPs also show minimal cross-reactivity with other classes of hydrolases such as cysteine-, metallo-, and aspartylhydrolases [59]. Furthermore, FP-based probes react only with the active serine hydrolase, and not the inactive zymogen, allowing these probes to interact only with functional species within the proteome [59]. Extensive use of this probe family has demonstrated their remarkable selectivity for serine hydrolases and resulted in the identification of over 100 distinct serine hydrolases... 

MODIFICATIONS OF THE METHOD It can be appropriate to coincubate the compound of interest in the presence of inhibitors of serum esterases. Used is sodium fluoride, physostigmin or ecothiophate iodide (Chien 1990 Quon et al. 1993). In case of carboxy- or aminopeptidase cleavage of peptides specific peptidase inhibitors like amastatin, bestatin, phenylmethylsulphonylfluoride, 1,10-phenanthroline or ethylenediamine tetra acetic acid (EDTA) are useful (Lee 1995). 

Enzymatic detoxification or modification AGAC antibiotics /(-Lactams Chloramphenicol Erythromycin Tetracyclines Mercury compounds Formaldehyde Modification by acetyltransferases, adenylylases or phosphotransferases Inactivation (/(-lactamases) Inactivation (acetyltransferases) Esterases produce anhydroerythromycin Enzymatic inactivation Inactivation (hydrolases, lyases) Dehydrogenase... 

Jokanovic, M., Stepanovic, R.M., Maksimovic, M., Kosanovic, M., Stojiljkovic, M.P. (1998). Modification of the rate of aging of diisopropylfluorophosphate-inhibited neuropathy target esterase of hen brain. Toxicol. Lett. 95 93-101. 

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