Redox Properties of Protein Disulfide Bond in Oxidized Thioredoxin and Lysozyme:  A Pulse Radiolysis Study

Abstract

We have studied the one-electron reduction of oxidized Chlamydomonas reinhardtii thioredoxin and compared it to that of hen egg white lysozyme, using CO(2)(*) (-) free radicals as reductants. This comparison shows that the thioredoxin disulfide/thiol redox couple has different properties than that of lysozyme: the disulfide radical pK(a) is much lower (around 5 for small disulfides, 4.62 for lysozyme, <3 for thioredoxin). To get a better understanding of the modulation of the thioredoxin redox properties we have constructed the mutants W35A and D30A. Their reduction by pulse radiolysis indicates that W35 strongly controls both the disulfide radical acidity (the pK(a) in W35A is equal to ca. 4), and the thiol reactivity. Asp30 is also involved in the control of proton transfer to the disulfide free radical. In addition, its removal seems to increase the reduction potential of the thioredoxin thiyl/thiol couple. Overall, the reduction properties of thioredoxin confirm its nature as a unique reductant.

Specific protein dynamics near the solvent glass transition assayed by radiation‐induced structural changes

“…Other studies using frozen solutions also show that solvent‐exposed parts of a protein are the most radiation‐sensitive (Filali‐Mouhim et al 1997; Audette et al 2000). However, sulfur‐containing groups differ not only in their solvent accessibility but also in their structural environment, which has been proposed to play an important role in defining the stability of a disulfide bond towards free radical attack (Ravelli and McSweeney 2000; Lmouméne et al 2000).…”

What can we learn from two‐center three‐electron bonding with the topological analysis of ELF?

“…The most extensively studied group is that of sulfur-centered radical cations, but they can also be found in anions [7,21,25,26,29] or neutrals adducts [24,27,28,30,36]. Time-resolved pulse radiolysis techniques have demonstrated that particularly the sulfur-containing species exhibit strong optical absorption in the visible and near UV regions.…”

Redox-Driven Signaling: 2-Oxo Acid Dehydrogenase Complexes as Sensors and Transmitters of Metabolic Imbalance

“…9A, control). Addition of thioredoxin, which is a scavenger of thiyl radicals (115), strongly increases the reaction rate at a delayed reaction time, that is, when the catalysis-associated inactivation becomes pronounced ( Fig. 9A).…”

“…Compared with thiyl radicals of monothiols, the thiyl radicals of dithiols are significantly more stabilized through their interconversion with the disulfide anion radical shown in Figure 7 (13). The disulfide anion radical exhibits reducing properties (E 0 = -1.6 V), while the thiyl radical is a strongly oxidizing species with E 0 from +0.75 to +1.33 V. The oxidizing potential depends on the tendency of the radical to be protonated (115). The protonation prevents the thiyl radicals of dithiols to close into the 3estructure of the moderate reductant, the disulfide anion radical (Fig.…”

“…Special focus of this review on the mechanistic details of ROS generation by the complexes highlights the coproduction of ROS with the complex-bound thiyl radicals, related to thioredoxin use as a thiyl radical scavenger (115) and an acceptor of electrons from dihydrolipoyl residues, alternative to NAD + (29,34,91). The alternative electron flow from the complex-bound dihydrolipoyl residues has also been shown for glutaredoxin (71).…”