Enzyme leukocyte elastase

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... 

Human leukocyte elastase is a protease that degrades elastin and other connective tissue components. It is implicated in the pathogenesis of pulmonary emphysema and other inflammatory diseases such as rheumatoid arthritis and cystic fibrosis. Porcine pancreatic elastase has often been used as a model for HLE. Both enzymes have a small primary binding site Si. 

In addition to the aforementioned allenic steroids, prostaglandins, amino acids and nucleoside analogs, a number of other functionalized allenes have been employed (albeit with limited success) in enzyme inhibition (Scheme 18.56) [154-159]. Thus, the 7-vinylidenecephalosporin 164 and related allenes did not show the expected activity as inhibitors of human leukocyte elastase, but a weak inhibition of porcine pancreas elastase [156], Similarly disappointing were the immunosuppressive activity of the allenic mycophenolic acid derivative 165 [157] and the inhibition of 12-lipoxygenase by the carboxylic acid 166 [158]. In contrast, the carboxyallenyl phosphate 167 turned out to be a potent inhibitor of phosphoenolpyruvate carboxylase and pyruvate kinase [159]. Hydrolysis of this allenic phosphate probably leads to 2-oxobut-3-enoate, which then undergoes an irreversible Michael addition with suitable nucleophilic side chains of the enzyme. 

Peptide chloromethyl ketone inhibitors have been developed for almost every serine protease that has been characterized adequately (30). For example, human leukocyte elastase, due to its involvement in emphysema, has been studied extensively with this class of inhibitor (32). The rate at which peptide chloromethyl ketones inhibit elastase is influenced by their interaction with the primary substrate binding site (Si) of the enzyme and by interactions at other subsites. The most effective chloromethyl ketone elastase inhibitor found thus far is MeO-Suc-Ala-Ala-Pro-ValCH2Cl (MeO-Suc- = CH3OCOCH2CH2CO-). This will not inhibit the other major leukocyte protease, cathepsin G (see Table VI). In contrast, Z-Gly-Leu-Phe-CH2C1 (Z = C6H5CH2OCO-) inhibits cathepsin G, but not elastase. Both enzymes can be inhibited with Ac-Ala-Ala-Pr o-V alCH2Cl. 

The reaction of human leukocyte elastase has been studied with a number of azapeptide p-nitrophenyl esters and some of the results are listed in Table VII. All of the azapeptides acylate elastase except Ac-Ala-Aphe-ONp, which reacts very slowly. However this azapeptide will react with cathepsin G as expected from the differing substrate specificity of the two enzymes. The kinetics of the reaction are described in detail elsewhere (36), but with most of the inhibitors, kCSLt is equal to the deacylation (or reactivation) rate of the acylated enzyme. Azapep-... 

Stein, R.L. and Strimpler, A.M. 1987. Catalysis by human leukocyte elastase aminolysis of acyl enzymes by amino acid amides and peptides. Biochemistry, 26, 2238-2242. 

Most enzymes present in the body play an essential biochemical role, but several of them also have an undesirable characteristic which requires selective suppression. Thus, the degrading effect of human leukocyte elastase on elastin (which provides elastic properties in several organs) requires selective inhibitors which are discussed in Chapter 2. 

Human leukocyte elastase inhibitors. HLE belongs to the chymotrypsin family of serine proteinases the enzyme consists of a single polypeptide chain of 218 amino acid residues and four disulfide bridges. HLE has been proposed to be a primary mediator of many pulmonary disorders such as em-... 

A. Janoff, B. Sloan, G. Weinbaum, V. Damiano, R. A. Sandhaus, J. Elias, and P. Kimbel. Experimental emphysema produced by purified human leukocyte elastase localization of the instilled enzyme. Am. Rev. Respir. Dis. 75 461 (1977). 

Human Leukocyte Elastase Activity and Other Hydrolytic Enzymes... 

Several 9-(phosphonoalkyl)- and 9-(difluoroalkyl)-guanine derivatives (12, X = H or F) have been studied as potential inhibitors of guanylate kinase. The most pronounced effect was observed with n - 5 Phenoxymethylene bisphosphonates (13, where R R and R represent a variety of substituents) were prepared and found to act as inositol phosphatase inhibitors and antimanic agents some inhibited the enzyme with IC50 < 50 pmol 4-(Phosphonomethylphenoxy)-l-carbamoylazetidine-2-ones (14) inhibited human leukocyte elastase for 14 (R R = OEt = 1.2 x 10 moL s (ref. 38). 

A series of ynenol lactones (stmcture 2) were studied as inhibitors of human leukocyte elastase (Tam et al., 1984 Spencer et al., 1986 Copp et al., 1987). Some of the compounds were alternate substrate inhibitors, being hydrolyzed by the enzyme to the reactive I but then deacylat-ing without an inactivation step. However, with the compound 3-benzyl ynenol butyrolactone (stmcture 2, where R = benzyl, R = H), the acyl-enzyme (E-I ) was stable enough to allow the second alkylation step, resulting in inactivated enzyme. All kinetic constants were determined. Continuous assays gave biphasic kinetics, the second minor phase possibly due to the presence of isozymes or enantiomers of the inhibitor. Immediate diffusion-limited inhibition was observed and gave a competitive Ki value of 4.3 0.7 xM. The first phase of inhibition was saturable, and analysis of the rates gave = 0.090 0.007 s , and... 

The inhibition of human leukocyte elastase by the ynenol lactone was irreversible in the presence of the nucleophiles )6-mercaptoethanol and hydroxylamine and after size exclusion chromatography. The partition ratio r was evaluated in two different ways. Titration of the enzyme by suicide substrate using the plot shown in Fig. 13.3 gave r = 1.7 0.5. The partition ratio was also determined from the ratio of rates 3/ 4= 1.5. 

Segel I.H, 1975, Enzyme Kinetics Behmrior and Analysis of Rapid Equilibrium and Steady-State Enzyme Systems, John Wiley Sons, ISBN 0-471-77425-1, Canada Sreerama, N. Woody, R.W. (2004). Computation and analysis of protein circular dichroism spectra. Methods Enzymol, Vol 383, pp 318-351 Stein, R.L., Stiimpler, A.M., Hoii, H. Powers, J.C., (1987). Catalysis by Human Leukocyte Elastase the Proton Inventory as a Mechanistic Probe. Biochemistry, Vol. 26, No.5, pp. 1305-1314... 

Cvetovich RJ, Chartran M, Hartner FW, Roberge C, Amato JS, Grabowski EJ. An asymmetric synthesis of L-694,458, a human leukocyte elastase inhibitor, via novel enzyme resolution of lactam esters. J. Org. Chem. 1996 61 6575 580. 

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