Equilibrium Constants of the Reactions of Sulfite with Cystine and with Dithiodiglycolic Acid

Kinetic study of the reaction between cystine and sulfide in alkaline solutions

“…It should be pointed out that different charge forms of CySSCy, CySH, and CySS-are also present under such conditions (8). This problem will be addressed below.…”

“…We generally found a good agreement between the calculated value for [CySS-I,, and the observed value from uv-visible spectroscopy (using €332 = 370 M-I cm-') or using Can (4) The equilibrium constants of reactions [3] and [4], Kl and reported k I = 0.8 M-' min-' at 20°C and unspecified IJ in an K,, are calculated from eqs. [8] and [9], respectively, unbuffered 0.1 M NaOH solution, whereas k-k2, and kL2 were all omitted in their approximation method. consider the first equilibrium (reaction [3]) and ignores the and their values at different pH are listed in Table 1.…”

“…The fact that the apparent equilibrium constants (I2) that the reaction rate vary with pH can be explained by the presence of different dx charge forms of CySSCy, CySH, CySS-, and HS-at different 1141 -= a p x yx2 pH. In order to determine the equilibrium constants due to other charge forms could then be calculated from the absolute the form (13) equilibrium constants at pH -14 and the apparent equilibrium constants at other pH (8). Unfortunately, such procedure is not [15] -tanh-'…”

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.…”

Free-radical chemistry of sulfite.

“…RSSR + HSO-z± RSSO-+ RSH (4) This reaction has an equilibrium constant of 0.089 at pH 7.75 and 37°C (9). The large concentration of RSSR causes most sulfite in the blood to be bound as S-sulfocysteine, RSS03-.…”