Esterase

Abstract: Part 1 General aspects: rate acceleration in enzyme-catalyzed reactions Michaelis-Menten kinetics enzyme inhibition specificity improvement or alteration of enzyme specifity enzyme stabilization and reactor configuration cofactor regeneration enzyme catalysis in organic solvents multienzyme systems and metabolic engineering rational design of new enzymatic catalysts references. Part 2 Use of hydrolytic enzymes - amidases, proteases, esterases, lipases, nitrilases, phosphatases, epoxide hydrolases: amidases protease-catalyzed peptide synthesis proteases that act as esterases acetylcholine esterase pig liver esterase phospholipases cholesterol esterase lipases nitrile hydrolysis enzymes epoxide hydrolase phosphatase references. Part 3 Oxidoreductions: nicotinamide cofactor dependent oxidoreductions dehydrogenases which utilize ketoacids as substrates other NAD(P)-dependent dehydrogenases oxidoreductases that are metalloenzymes references. Part 4 C-C bond formation: aldol condensation ketol and aldol transfer reaction addition of HCN to aldehydes acyloin condensation C-C bond forming reactions involving acetyl coA isoprenoid and steroid synthesis replacement of chloroalanine C-C bond formation catalyzed by vitamin B[12] references. Part 5 Synthesis of glycoside bonds: background glycosyltransferases of the Leloir pathway substrate specificity and synthetic applications of glycosyltransferases non-leloir glycosyltransferases glycosidases transglycosidases synthesis of N-glycosides biological applications of synthetic glycoconjugates future opportunities references. Part 6 Addition, elimination and other group transfer reactions (phosphoryl-, methyl-,sulpho-and amino-transfer reactions): addition of water to alkenes - fumarase addition of ammonia to double bonds - ammonia lyases transamination - aminotransferases addition and elimination of carboxyl group nucleoside triphosphate requiring enzymatic reactions preparation of ATP chiral at -, - or - phosphorous phosphorothioate-containing DNA and RNA DNA and RNA oligomers incorporation of modified or unnatural bases into DNA or RNA dehalogenation synthesis of chiral methyl groups S-adenosylmethionine and transmethylation sulfate activation and transfer reactions.

Abstract: The mechanism of cholinergic neurotransmission requires the rapid inac­ tivation of acetylcholine (Dale 1914). Loewi & Navratil showed in 1926 that acetylcholine can be destroyed by an enzyme that exists in aqueous extracts of frog tissues. An esterase that specifically hydrolyzes choline esters was characterized in horse serum by Stedman et al (1932), who called it choli­ nesterase. It was later found that blood cells also contain a high level of acetylcholine-hydrolyzing activity (Stedman & Stedman 1935). Alles & Hawes (1940) subsequently found that in human blood the serum and cell enzymes are qualitatively different; Mendel et al (1943a) showed that, al­ though the serum enzyme hydrolyzes butyrylcholine or propionylcholine faster than acetylcholine [as already noted by Stedman et al (1932)], the cell-bound enzyme acts preferentially on acetylcholine, at low substrate concentration. The particulate enzyme also presents a characteristic excess substrate inhibition, so that its activity varies, in a bell-shaped manner, as a function of substrate concentration (Mendel & Rudney 1943). These two activities exist in all classes of vertebrates. The serum enzyme (Be 3.1.1.8) varies somewhat in its specificity, notably in the relative rates of hydrolysis of propionylcholine and butyrylcholine (Augustinsson 1959a,b). The serum enzyme was called originally "nonspecific" cholineste­ rase, or "pseudocholinesterase" (Mendel et al 1943, Mendell & Rudney 1943). In contrast, the erythrocyte enzyme (EC 3.1.1.7) was considered the

Abstract: Both human carbonic anhydrases B and C act as esterases on o- and p-nitrophenyl acetates Enzyme C is the more active of the two for the hydrolysis of p-nitrophenyl acetate, and enzyme B for o-nitrophenyl acetate The pH-activity curves are sigmoid, the esterase activity being very small below pH 6 and rising to a high level around pH 9; the inflection point lies at pH 73 for Enzyme B and at 68 for Enzyme C The Km values are nearly independent of pH in all cases; thus the pH dependence curves appear to reflect the catalytic center activity The reactions follow Michaelis-Menten kinetics over the range of substrate concentrations studied, but this range is limited to values less than the Km values, because of the limited solubility of the esters Measurements in a stop-flow apparatus, at times from 10 msec to 2 sec, gave the same kinetic constants as those measured under steady state conditions There was no evidence of an initial "burst" of release of nitrophenol When the reactions were studied under the condition (E0) ≅ (S0) << Km, the process followed first order kinetics until hydrolysis was nearly complete The data thus gave no evidence for the presence of an acyl intermediate; if such an intermediate exists it must be very rapidly hydrolyzed Both enzymes are inhibited by monovalent anions, by acetazolamide, and by alcohols Anion inhibition decreases with increasing pH, and so does the acetazolamide inhibition The alcohol inhibition is not affected by pH Enzyme B is somewhat more strongly inhibited by anions, but Enzyme C is much more strongly inhibited by alcohols and by acetazolamide Only one site seems to be involved in the inhibition by either type of inhibitor Competition for one site has been demonstrated between the anions and the alcohols The inhibitions are reversible, and noncompetitive with respect to substrate Since anion inhibition follows the lyotropic series, the binding site is believed not to be the zinc ion Binding of anions by Enzyme B, and by zinc-free apoenzyme, has been demonstrated by an increase in pH of an isoionic solution caused by the addition of neutral salts At low salt concentrations solutions of the apoenzyme show a lower change in pH than these of the holoenzyme, but at higher salt concentrations the values are very similar Thus in 01 m KCl both the enzyme and apoenzyme bind approximately 6 chloride ions

Abstract: The esterase enzymes of the tissues of Atlantic herring (Clupea harengus harengus) were analyzed by starch gel electrophoresis. Four sets of esterase bands were distinguished by their electrophoretic mobility, their relative activity with the two substrates, alpha-naphthyl acetate and alpha-naphthyl butyrate, and their relative concentrations in plasma, liver, and heart tissues. All of the esterases were inhibited by 10−4M solutions of dichlorvos, an organophosphate inhibitor, but none was inhibited by 10−4M eserine sulfate or by 10−4 M EDTA. Polymorphism was noted in all four sets of esterases. Evidence for the genetic control of the fastest migrating set was obtained from population genetic analyses. In this set of esterases, five distinct bands occurred either singly or in pairs. The observed distribution of the three most common bands fits the hypothesis that they are controlled by a set of autosomal alleles. The two rarest bands occurred only in the heterozygous state, as would be expected. ...

Abstract: Evidence is presented that human serum contains a single enzyme with both paraoxonase and arylesterase activities. Throughout the steps of purification and after obtaining over 600-fold purification of the enzyme, the arylesterase activity (measured with phenylacetate as the substrate) co-eluted and retained the same ratio of activity to paraoxonase activity as it had in the initial plasma sample. Paraoxon and DFP (diisopropylfluorophosphate) both complete with phenylacetate as substrates; the inhibition is of mixed type with paraoxon and competitive with DFP. Paraoxonase and arylesterase activities require calcium, and both are inhibited to the same degree by EDTA. Purified arylesterase/paraoxonase is a glycoprotein with a minimal molecular weight of about 43,000. It has up to three sugar chains per molecule, and carbohydrate represents about 15.8% of the total weight. The enzyme has an isoelectric point of 5.1. Its amino acid composition shows nothing unusual, except for a relatively high content of leucine. We conclude that human serum arylesterase and paraoxonase activities are catalyzed by a single enzyme, capable of hydrolyzing a broad spectrum of organophosphate substrates and a number of aromatic carboxylic acid esters. Studies on the genetically determined polymorphism responsible for two allozymic forms (A and B) of the esterase are described in the following paper.