The estimation of thiols and disulphides by potentiometric titration with silver nitrate

Abstract

This paper describes further developments in the estimation of thiols by potentiometric titration with silver nitrate. A previous paper (Cecil, 1950)

Dissociation and reduction of covalent β-lactoglobulin–quinone adducts by dithiothreitol, tris(2-carboxyethyl)phosphine, or sodium sulfite

“…Different reaction mechanisms were proposed for the reduction of b-LG and b-LG-Q by each 34 of the reducing agents. These results show that on reductive sample preparation for analysis of protein 35 samples, not only are protein polymers formed through oxidative disulfide bonds reduced into the 36 individual protein constituents but also a large part of any protein-phenol adducts present will dissociate 37 and, thus, give a false picture of the level of protein-protein interactions that have occurred in 38 the sample. 39 Ó 2015 Elsevier Inc. All rights reserved.…”

“…Under more alkaline conditions, the reactivity 400 decreases due to repulsion between the sulfite in its dianionic form 401 and the negative charges of the protein side chains in the vicinity 402 of the disulfides [36]. Furthermore, the reduction of disulfides by 403 sodium sulfite is reversible when pH is not considerably lower than 404 the pK a of the thiol, and the reverse reaction is dependent on the 405 amount of thiolate anion (RS À ) formed [37,38]. Hence, because 406 the reduction in the current study was performed at pH 8 Note.…”

A kinetic study of the reactions on some disulphides with sodium sulphite

“…Reagents. The materials used have been described previously (Cecil & McPhee, 1955). 0O1M-Na2SO3 solutions were made up daily and stabilized by the addition of ethylenediaminetetraacetic acid (EDTA) to a concentration of 2 mM, since without EDTA, small volumes of solutions could decompose to the extent of 20-30 % during a day at room temperature.…”

Further studies on the reactions of disulphides with sodium sulphite

“…The methods of estimation for homocystine and five other disulphides (by allowing them to react with Na%SO3 and titrating the thiol formed with AgNO3) have been reported (Cecil & McPhee, 1955a), and methods for five more disulphides are sumnnarized in Table 1. The corresponding thiols have not been studied as pure substances but only as disulphidesulphite reaction mixtures.…”