A study of the kinetics of the reaction between thiol compounds and chloroacetamide

Lindley, H.

doi:10.1042/bj0740577

Cited by 103 publications

(57 citation statements)

References 3 publications

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“…I n the case of cysteine and similar amino thiol compounds the dissociation of the SH group is complicated by the overlapping dissociation of the amino group. The simple form of equation ( 2 ) holds only, if the two constants do not influence each other and the reaction rate of RS-is not changed by the dissociation ofthe amino group [14,15,16]. So equation ( 2 ) is only an approximation which is applicable in limited pH regions.…”

Section: A-amentioning

confidence: 99%

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Stereospecific Alkylation with Asymmetric Reagents

Wallenfels

Eisele

1968

European Journal of Biochemistry

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1.When undergoing nucleophilic reactions with proteins, a-iodopropionic acid and its amide show greater specificity for SH groups than do iodoacetic acid and its amide.2. The kinetics and stereochemistry of the reactions of the D( +) and L( -) antipodes of a-iodopropionic acid and its amide with both cysteine and papain were investigated. The antipodes of the SH reagents reacted with these asymmetric SH compounds a t different rates. I n the reaction with papain, the L( -) antipode of the acid reacted faster than the D(+) antipode; the stereochemical preference was inverted when the amide was used, the D(+)antipode reacting faster than the L( -)antipode. 3.Arguing from the differing reactivities of the SH reagents and their antipodes and the pH dependence of the reaction rates, it has been suggested, that L( -)a-iodopropionic acid is specifically oriented onto the reaction center through the concerted attractive and repulsive actions of a cationic and an anionic group in the protein. These have been tentatively identified as a protonated imidazole residue and a carboxylate group respectively.4. Parallels between these stereospecific alkylations and the catalytic action of the enzyme are discussed.Gundlach, Stein, and Moore [1] demonstrated in their studies of the alkylation of ribonuclease with iodoacetic acid and iodoacetamide, that these "classic" sulfhydryl reagents do not react only with SH groups. Other nucleophiles present in proteins, such as amino, imidazolyl or thioether groups may also be alkylated. The extent of these side reactions depends on the reaction conditions. Our purpose in undertaking this work was to find SH reagents with higher selectivity for SH groups.Reasoning from a theory of Bunnett [a] it seemed likely, that this could be achieved by the introduction of polarizable substituents alpha to the halogen of halogen-alkyles. The possibility for the action of dispersion forces, which is introduced with the polarizable substituent, should specially favor the transition state for the reaction with the highly polarizable SH group. Steric, inductive or mesomeric effects of the a substituent would be expected to show the same influence on the reactions with all different nucleophilic groups.We tested this hypothesis using a series of derivatives of iodoacetamide with different substituents alpha to the iodine. With the methyl group as CI substituent i e . in the reaction of amino acids with a-iodopropionamide we observed an enhanced selectivity for SH groups as predicted by Bunnett's theory A further possibility for selective reactivity is contributed by a-substitution in iodoacetic acid derivatives ; the leaving group of the reagent is attached to an asymmetric carbon atom. One may expect specific interactions if the substrate itself is asymmetric since diastereomeric transition states are involved. This type of stereoselective reaction was shown for the first time by Heinrikson et al. [4,5]. They found, that the essential histidine (residue 12) of ribonuclease reacts preferentially with the D-...

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Section: A-amentioning

confidence: 99%

“…Lindley [14] has derived mathematical expressions for the pH dependence of the allrylation rate of dissociable SH compounds where RS-is the reacting species :…”

Section: A-amentioning

confidence: 99%

Stereospecific Alkylation with Asymmetric Reagents

Wallenfels

Eisele

1968

European Journal of Biochemistry

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“…Generally, thiols are alkylated in their anion form [37] so that the alkylation rate is enhanced with increasing pH corresponding to the titration behaviour of the sulfhydryl group. Apparently, no ionization of the type mercaptan -+ mercaptide occurs for the reactive sulfhydryl group in the pH range studied.…”

Section: Carbamoylmethyl Incorporation At Different Temperaturesmentioning

confidence: 99%

Reaction of Yeast Fatty Acid Synthetase with Iodoacetamide

Oesterhelt

Bauer

Kresze

et al. 1977

European Journal of Biochemistry

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Yeast fatty acid synthetase is inactivated by several SH reagents. For the irreversible inhibition by iodoacetamide, the apparent second-order rate constant k = 1.3 f 0.2 M-' sC1 was found (0 "C, pH 6.5). This value is about 125-times higher than the rate constant for the reaction between iodoacetamide and free cysteine under the same conditions and was found to be pH-independent in the range between pH 5 and pH 9. A possible explanation for this result might be that the SH-group alkylated by iodoacetamide is hydrogen-bonded to a neighbouring basic group in the protein.Of all partial activities of the synthetase, only the condensation reaction is impaired. The enzyme can be protected against iodoacetamide by prior treatment with acetyl-CoA but not malonyl-CoA. This indicates that iodoacetamide reacts with peripheral

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“…We also found a higher percentage of Hcy-S-S-Hcy in the endothelium than in plasma. Hcy-S-S-Hcy has a greater ability to form stable disulfide bonds with protein cysteine residues at physiological pH than does Hcy even in the presence of other thiols (29). Due to the electron/proton donating properties of histidyl and tyrosyl moieties in proteins, the sulfhydryl group of cysteinyl moieties typically exhibit lower pK a values than that of the free amino acid (ϳ5-6 vs. 8.3) (33).…”

Section: Discussionmentioning

confidence: 99%

Role of homocysteinylation of ACE in endothelial dysfunction of arteries

Huang

Pinto

Froogh

et al. 2015

American Journal of Physiology-Heart and Circulatory Physiology

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The direct impact of de novo synthesis of homocysteine (Hcy) and its reactive metabolites, Hcy-S-S-Hcy and Hcy thiolactone (HCTL), on vascular function has not been fully elucidated. We hypothesized that Hcy synthesized within endothelial cells affects activity of angiotensin-converting enzyme (ACE) by direct homocysteinylation of its amino-and/or sulfhydryl moieties. This covalent modification enhances ACE reactivity toward angiotensin II (ANG II)-NADPH oxidase-superoxide-dependent endothelial dysfunction. Mesenteric and coronary arteries isolated from normal rats were incubated for 3 days with or without exogenous methionine (Met, 0.1-0.3 mM), a precursor to Hcy. Incubation of arteries in Met-free media resulted in time-dependent decreases in vascular Hcy formation. By contrast, vessels incubated with Met produced Hcy in a dose-dependent manner. There was a notably greater de novo synthesis of Hcy from endothelial than from smooth muscle cells. Enhanced levels of Hcy production significantly impaired shear stress-induced dilation and release of nitric oxide, events that are associated with elevated production of vascular superoxide. Each of these processes was attenuated by ANG II type I receptor blocker or ACE and NADPH oxidase inhibitors. In addition, in vitro exposure of purified ACE to Hcy-S-S-Hcy/HCTL resulted in formation of homocysteinylated ACE and an enhanced ACE activity. The enhanced ACE activity was confirmed in isolated coronary and mesenteric arteries that had been exposed directly to Hcy-S-S-Hcy/HCTL or after Met incubation. In conclusion, vasculature-derived Hcy initiates endothelial dysfunction that, in part, may be mediated by ANG II-dependent activation of NADPH oxidase in association with homocysteinylation of ACE.

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A study of the kinetics of the reaction between thiol compounds and chloroacetamide

Cited by 103 publications

References 3 publications

Stereospecific Alkylation with Asymmetric Reagents

Stereospecific Alkylation with Asymmetric Reagents

Reaction of Yeast Fatty Acid Synthetase with Iodoacetamide

Role of homocysteinylation of ACE in endothelial dysfunction of arteries

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