Nuclear magnetic resonance studies of the acid–base chemistry of amino acids and peptides. IV. Mixed disulfides of cysteine, penicillamine, and glutathione

Abstract

. Can. J. Chem. 62, 13 12 (1984). The acid-base chemistry of the ammonium groups of penicillamine-glutathione mixed disulfide and cysteine-glutathione mixed disulfide has been characterized by I3C nmr and that for the ammonium groups of penicillamine-cysteine mixed disulfide by 'H nmr. ' The mixed disulfides were formed by thiol/disulfide exchange. Chemical shift titration data were obtained simultaneously for the mixed disulfides, the thiols, and the symmetrical disulfides in the mixture. Since the fractional titration of individual ammonium groups can be obtained directly from chemical shift data, it was not necessary to isolate the mixed disulfides. The chemical shift data indicate that the two ammonium groups of each of the mixed disulfides are titrated over the same pH range, with the acidity of the ammonium group of the penicillamine and cysteine parts of the penicillamineglutathione and cysteine-glutathione mixed disulfides 4.4 and 3.9 times as acidic as those of the glutathione part. In the penicillamine-cysteine mixed disulfide, the penicillamine ammonium group is 1.7 times as acidic as that of the cysteine part. Macroscopic and microscopic acid dissociation constants are reported for each of the mixed disulfides. The advantages of nmr as a method for characterizing the acid-base chemistry of mixed disulfides are discussed.YVON THERIAULT, BRUCE V. CHEESMAN, ALAN P. ARNOLD et DALLAS L. RABENSTEIN. Can. J. Chem. 62, 13 12 (1984). On a caractCrisC la chimie acide-base des groupes ammonium des disulfures mixtes pCnicillamine-glutathion et cystCine-glutathion en faisant appel 21 la rmn du I3C et celle des groupes ammonium du disulfure mixte penicillamine-cysttine par la rmn du 'H. Les disulfures mixtes ont CtC obtenus via un tchange thiol/disulfure. On a obtenu simultankment les donnCes de titrage du diplacement chimique pour les disulfures mixtes, les thiols et les disulfures symktriques du melange. I1 n'est pas nicessaire d'isoler les disulfures mixtes puisqu'on peut obtenir directement le titrage fractionnel des groupes ammonium individuels B partir des donnCes de dtplacement chimique. Ces donnCes indiquent que les deux groupes ammonium de chaque disulfure sont titrCs dans le m&me domaine de pH. Les aciditis des groupes ammonium des portions pCnicillamine et cystkine des disulfures mixtes pinicillamine-glutathion et cystkine-glutathion sont respectivement 4,4 et 3,9 fois plus tlevies que celle de la partie glutathion. Dans le disulfure mixte p6nicillamine-cystkine 1'aciditC du groupe ammonium de la ptnicillamine est de 1,7 fois plus ClevCe que celle de la cystiine. On rapporte les constantes macroscopique et microscopique de dissociation acide pour chaque disulfure mixte. On discute des avantages de la rmn en tant que mtthode de caracttrisation de la chimie acide-base des disulfures mixtes.[Traduit par le journal] Introduction Thiols are oxidized by disulfides in two steps:

Zn(II) Complexes of Glutathione Disulfide: Structural Basis of Elevated Stabilities

“…Protonation constants of GSSG (Scheme ) were obtained by potentiometry at four temperature values, 19, 25, 30, and 37 °C, to enable calculations of thermochemical parameters of protonation phenomena. These constants are presented in Table and are in good agreement with the previous determinations at 25 °C ,− and at 37 °C. , The constants determined at 25 °C were published previously in our study on Ni(II) complexes of GSNO and GSSG . A reliable determination of the sixth most acidic constant by potentiometry was impossible under our experimental conditions.…”

“…Values of protonation macroconstants of GSSG, as mentioned above, agree well with those determined previously. ,,,, The value of p K 6 , determined by NMR, is in excellent agreement with the most recent reports. , This value is lower than a practical acidic limit for determinations using pH-metric titrations of millimolar compounds, ca. 2.0.…”

Selenium-77 nuclear magnetic resonance studies of selenols, diselenides, and selenenyl sulfides

“…The exchange-averaged 'H resonances observed for solutions containing selenol and diselenide are in sharp contrast with the separate resonances observed for thiol and for disulfide in both 'H and I3C spectra of solutions containing thiol and disulfide (18)(19)(20), indicating that selenol/diselenide exchange is much faster than thiol/disulfide exchange.…”

“…By analogy with results from 'H and 13C nmr studies of thiol/disulfide exchange reactions (18)(19)(20), we expected to observe separate resonances for selenol and diselenide. However, 'H resonances were either broadened or exchange-averaged, depending on pH and the relative concentrations of selenol and diselenide, and 77Se resonances could not be detected for selenol/diselenide mixtures.…”

Novel glutathione analogues containing the dithiol and disulfide form of the Cys-Cys dyad

“…4.4ppm) (Lift et al, 1996). A characteristic feature (Theriault et al, 1984;Calcagni et al, 1996) of the 13C-NMR spectrum of 6 is represented by the resonances of the two Cys fl-carbon atoms (28.15 and 28.80 vppm) which are shifted at higher field as compared with the corresponding atoms in the disulfde precursor 5 (49.92 and 45.77 6 ppm). The electrospray mass spectrum (ES-MS) of 5 shows the formation of both M + H + and 2M + H + species.…”