N‐(2‐Oxoacyl)amino Acids and Nitriles as Final Products of Dipeptide Chlorination Mediated by the Myeloperoxidase/H₂O₂/Cl⁻ System

Abstract

The chlorination of dipeptides by the myeloperoxidase/H20~/C1-system takes place at the N-terminal amino group, whereas no chlorination of the amide nitrogen of the peptide bond can be observed. The N-terminal amino group is chlorinated to N-monochloroamine or/and N-dichloroamine. N-Monochloropeptides were the main products at higher pH values, at lower pH a mixture of N-monochloropeptides and N-dichloropeptides was formed owing to the dismutation of N-monochloroamine to N-dichloroamine.N-Monochloropeptides decompose, yielding NH3 and the corresponding N-(2-oxoacyl)amino acids. N-Dichlorodipeptides decompose faster but to nitriles and the free C-terminal amino acids. N-Dichloroglycyl-amino acid decomposes through a relatively stable intermediate (cyano-formylamino acid) to hydrogen cyanide, cyanogen chloride and the free C-terminal amino acid. lnsulin chlorination also yields N-terminal glycyl and phenylalanyl N-monochloro derivatives, which deaminate to glyoxylyl and phenylpyruvyl residues.Myeloperoxidase of polymorphonuclear neutrophilic granulocytes catalyses the oxidation of CIions to HOCl by hydrogen peroxide [1-31. The chlorinating ability of myeloperoxidase seems to be important for the bactericidal mechanisms of neutrophils [4-61. The physiological role of the chlorination process was emphasized by its discovery in granulocytes undergoing phagocytosis [7]. Peptides and proteins may be target substrates for chlorination during phagocytosis. The incorporation of 36Cl into bovine albumin by purified myeloperoxidase was reported [7].From the chemical point of view, many different functional groups in protein are susceptible to HOCl attack : e.g. amino, imidazolium, guanidinium, indole residues, phenolic rings and the amide nitrogen of peptide bonds. In the enzymatic reaction, however, HOCl production by myeloperoxidase is impaired when the chlorination or oxidation of the HOClreactive substrate is slower than that of the enzyme itself. In such cases autodestruction of niyeloperoxidase occurs.Abbreviations. AcAla, N-acetyl-alanine; CIGly-Leu, N-monochloroglycyl-leucine; CIAla-Ala, N-monochloroalanyl-aianine; ClLeu-Gly, N-monochloroleucyl-glycine; ClzCly-Leu, N-dichloroglycyl-leucine.Enzyme. Myeloperoxidase (EC 1.11.1.7).It was established that amino compounds are effective acceptors of C1' ions formed in myeloperoxidase-mediated reactions [2,8] and protect myeloperoxidase against HOCl attack [9].Preliminary examination of bovine albumin chlorination by the myeloperoxidase system showed that 36Cl incorporated into protein was to a great extent K1-reactive, i.e. N-CI bonds were formed. These results focussed attention on the chlorination of the protein amino groups (N-terminal and 8-lysine amino groups) and the amide nitrogen of peptide bonds.It seemed reasonable to start the systematic elucidation of protein chlorination by examining the reactions of simple dipeptides without side-chain functional residues. This made it possible to check the reactions only of N-terminal amino groups and of the peptidebond ami...

Neutrophils convert tyrosyl residues in albumin to chlorotyrosine

“…Others have shown that hypochlorous acid reacts with proteins by preferentially oxidising cystyl, methionyl, and tryptophanyl residues, and chlorinating amine groups [15][16][17]. The latter breakdown to form aldehydes and nitriles [18]. Although chlorotyrosine is a minor reaction product, it is the only modification of proteins identified to date that is unique to hypochlorous acid.…”

Modification of High Density Lipoprotein by Myeloperoxidase Generates a Pro-inflammatory Particle

“…Moreover, N ⑀ -dichloramine formation is also a relatively facile reaction, although the final decomposition product(s) formed are less clear. In model dipeptide systems where halogenation of the N termini formed N ␣ -dichloramines, nitriles were one of the observed products (54). Alternatively, chlorination of the N termini of target proteins has also been reported to generate multiple deamination derivatives (54).…”

“…In model dipeptide systems where halogenation of the N termini formed N ␣ -dichloramines, nitriles were one of the observed products (54). Alternatively, chlorination of the N termini of target proteins has also been reported to generate multiple deamination derivatives (54). Even the amide bond itself within a polypeptide is a potential target for halogenation by HOCl, forming chloramides.…”

Neuronal expression of myeloperoxidase is increased in Alzheimer's disease

“…The best characterized role of myeloperoxidase is in host defense (Klebanoff and Clark 1978;Hurst and Barrette 1989;Gaut et al 2001) where the enzyme converts hydrogen peroxide generated from the oxidative burst to the potent microbicidal oxidant hypochlorous acid (HOCl; Harrison and Schultz 1976). HOCl chlorinates electron-rich substrates (Klebanoff and Clark 1978;Hurst and Barrette 1989), generates protein carbonyls (Yan et al 1997), and converts free amino acids to reactive aldehydes (Stetmaszynska and Zgliczynski 1978;Anderson et al 1997) that contribute to formation of AGEs (Anderson et al 1999). Myeloperoxidase also oxidizes nitrite to reactive nitrogen species (Eiserich et al 1998;Byun et al 1999) and converts tyrosine to tyrosyl radical, a reactive intermediate that promotes o,o¢-dityrosine formation and initiates lipid peroxidation (Heinecke et al 1993;Savenkova et al 1994).…”