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In this study, we synthesized a zwitterionic DTNB derivative, 5-(2-aminoethyl)-dithio-2-nitrobenzoate (ADNB), and characterized its reactions with several cationic, anionic, and neutral thiols. Reactions with ADNB, unlike those with DTNB, are relatively insensitive to electrostatic environments and ionic strengths. At relatively low ionic strength, rate ratios, k ADNB / k DTNB , varied from 0.22 for reactions with low-molecular-weight cationic thiols to 3.0 for those with low-molecular-weight anionic thiols. A k ADNB / k DTNB ratio of ∼200 for Cys-34 of BSA appears to reflect a very anionic environment. k ADNB / k DTNB ratios of ∼6 and ∼1, respectively, for canine and equine serum albumins, which have Glu-82 → Asp and Glu-82 → Ala substitutions suggest Glu-82 is the most important anionic residues affecting the reactivity of Cys-34 in BSA. k ADNB / k DTNB ratios appear to be useful for characterizing electrostatic environments of thiol groups in proteins.

Model dithiol compounds were S-nitrosated and the kinetics of their decompositions were studied. Rate constants for intramolecular homolysis of dinitrosated dithiols varied from 1.6 to 10 × 10−3 s−1. Rate constants for intramolecular heterolysis of mononitrosated dithiols varied from 4 to 32 × 10−4 s−1. Similar reactions may account for the effects of NO and nitrovasodilators on some enzymes.

Potentially dangerous nitrosamines have been shown to result from the reaction of sodium nitroprusside with several drugs under physiological conditions (pH 7.3 and 37°C). In each case the products were identical to those produced upon reaction with nitrous acid at much lower pH values. Reaction rates were shown to reflect a first order dependence on both amine and nitroprusside concentrations and to increase at higher pH values, approximately in proportion to concentrations of unprotonated amine. Fast reactions of sodium nitroprusside with reduced glutathione, cysteine, and ascorbate suppress but do not prevent the conversion of amines into N-nitrosamines. These results show sodium nitroprusside to be very potent nitrosating agent under physiological conditions and suggests nitrosamines may be formed during its normal pharmacological administration.

The S-nitroso derivative of 5-thio-2-nitrobenzoate was synthesized from 5,5'-dithiobis(2-nitrobenzoic acid) and partially characterized. Although relatively unstable, it is easy to prepare and reacts very rapidly with thiols and thiol groups of proteins to give corresponding S-nitrosothiols and 5-thio-2-nitrobenzoate dianion. The latter's easy spectrophotometric detection makes such reactions easy to follow and to quantitate.

Amino groups of proteins can be alkylated by reaction with a variety of aldehydes or ketones in the presence of several different mild reducing agents. Because reductive alkylation occurs under mild conditions and has relatively minor effects on most proteins, it is becoming one of the more important methods for protein modification. This report discusses some of the recent applications of this reaction.

Carboxyl groups of tobacco mosaic virus protein were modified by several amines using 1-ethyl-3-(dimethylaminopropyl) carbodiimide. A high yield of soluble protein which did not extensively aggregate at pH 5 was obtained only with ethylenediamine. The extent of modification could be varied depending on the excess of carbodiimide used. Upon modification of 6 carboxyl groups per subunit with ethylenediamine a product was obtained differing slightly from unmodified tobacco mosaic virus (TMV) protein in its optical rotatory dispersion and circular dichroism spectra and in its ability to polymerize into virus-like particles. At pH 5 this protein had a sedimentation coefficient of 4 S and was thus a low molecular weight aggregate, probably a trimer. It was able to form virus-like particles in the presence but not in the absence of TMV RNA. Substitution of 2 additional carboxyl groups gives further depolymerization, preventing the formation of virus-like particles even in the presence of TMV RNA. The later product also differs slightly from unmodified TMV protein in its optical rotatory dispersion and circular dichroism spectra and at pH 5.0 has a sedimentation coefficient of 1.4 S and therefore appears to be a monomer.

Reactions de l'octylamine avec l'acide nitraux aqueux a pH faible et avec l'ion nitroprussiate dans des conditions basiques

Publisher Summary Many simple aldehydes and ketones react rapidly and reversibly with amino groups of proteins. Neither the initial adduct or the Schiff base formed upon dehydration is very stable in dilute aqueous solution, but extensive modification of protein amino groups can be obtained by the reduction of the Schiff base to a stable secondary amine. Reductive alkylation of protein amino groups can, thus, be accomplished with many different aldehydes and ketones under very mild conditions by using sodium borohydride as the reductant. Under the conditions described in the chapter, both α- and ɛ-amino groups are readily modified, but other common protein groups are not affected. Because the modified groups experience only a small change in basicity and, at neutral pH, retain their normal cationic charges, the overall charge and the relative distribution of charged groups in most proteins are not greatly changed by reductive alkylation. By using a large variety of readily available aldehydes and ketones, the size, shape, and hydrophobicity of added substituents can be easily varied. Reductive alkylation procedure is applicable to most proteins, except those containing readily reducible components or prosthetic groups, such as pyridoxal phosphate and rhodopsin, or those which are not stable at the required alkaline pH values.

Radioactivity from ingested ϵ-N-[3H] methyl-and ϵ-N-[3H]-dimethyllysine residues of reductively methylated casein are rapidly and efficiently absorbed and incorporated into tissues of the chicken. Introduction of label into choline, carnitine and methionine suggests that these amino acids contribute methyl groups to the one-carbon pool.

Glutathione was converted by HNO2 into a S-nitrosothiol which was stable in solution and atypically so even as a solid. FAB/MS and IR data have been obtained for the confirmation of structure of S-nitrosoglutathione in the crystalline state.

A simple column reactor containing a small amount of palladium catalyst, in the form of palladium black, and formic acid as a hydrogen donorcan be used to hydrogenate several types of olefins.