| Abstract
| - Diselenide bonds are intrinsically more stable than disulfide bonds. To examine how this stabilitydifference affects reactivity, we synthesized selenoglutathione (GSeSeG), an analogue of the oxidizedform of the tripeptide glutathione that contains a diselenide bond in place of the natural disulfide. Thereduction potential of this diselenide bond was determined to be −407 ± 9 mV, a value which is 151 mVlower than that of the disulfide bond in glutathione (GSSG). Thus, the diselenide bond of GSeSeG is7 kcal/mol more stable than the disulfide bond of GSSG. Nonetheless, we found that GSeSeG can beused to oxidize cysteine residues in unfolded proteins, a process that is driven by the gain in proteinconformational stability upon folding. Indeed, the folding of both ribonuclease A (RNase A) and bovinepancreatic trypsin inhibitor (BPTI) proceeded efficiently using GSeSeG as an oxidant, in the former casewith a 2-fold rate increase relative to GSSG and in the latter case accelerating conversion of a stablefolding intermediate to the native state. In addition, GSeSeG can also oxidize the common biologicalcofactor NADPH and is a good substrate for the NADPH-dependent enzyme glutathione reductase(kcat = 69 ± 2 s-1, Km = 54 ± 7 μM), suggesting that diselenides can efficiently interact with the cellularredox machinery. Surprisingly, the greater thermodynamic stability of diselenide bonds relative to disulfidebonds is not matched by a corresponding decrease in reactivity.
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