Photolysis of an Intrachain Peptide Disulfide Bond: Primary and Secondary Processes, Formation of H₂S, and Hydrogen Transfer Reactions

Abstract

The photodissociation of intrachain disulfide bonds in a model peptide and salmon calcitonin generates a series of cyclic peptide products following the generation of a CysS(*) thiyl radical pair. Key to the formation of these cyclic products are disproportionation and reversible hydrogen atom transfer reactions as well as secondary photoreactions, which lead to C-S bond breakage of primary photoproducts. Depending on the wavelength of the incident light, disulfides ultimately convert into cyclic thioethers. An important photolytic product is H(2)S, which is highly relevant for the production and storage of protein pharmaceuticals, where H(2)S can catalyze disulfide scrambling and protein degradation.

Photolysis of Recombinant Human Insulin in the Solid State: Formation of a Dithiohemiacetal Product at the C-Terminal Disulfide Bond

“…4, squared ions), provide evidence for the formation of a crosslink between Cys[B19] and Tyr[A19] in solution. Initially, we had reported product IV as the only crosslink formed in solution (22), but the higher quality of our MS/MS data in the current paper together with our recent mechanistic understanding of dithiohemiacetal formation in solution (18,20) now permits us to identify the formation of both III and IV in solution. In the solid, the yield of product III was sufficient for detection by the QTOF-2 instrument.…”

“…Products (20). For the latter peptides, we have characterized subsequent reactions which convert dithiohemiacetal to thioethers (prolonged UV exposure) or vinyl-sulfides and trisulfides (exposure to 40°C for 8 h).…”

“…Well-established photoproducts from Trp, Tyr, and cystine include N-formylkynurenine, oxoindole, dityrosine, sulfonic and sulfinic acid. The disulfide bond is sensitive to light-induced degradation, where recent studies with model peptide have indicated the formation of a series of novel photoproducts such as dithiohemiacetals, and thioethers (18)(19)(20)(21). Additionally, in a previous publication, we investigated in particular the mechanisms of photodegradation of human insulin in solution through the formation of S-centered radicals, where evidence for chemical cross-linking between the A-and B-chain was obtained, together with significant extent of covalent H/D exchange when experiments were carried out in D 2 O (22).…”

“…Mechanistic details on the formation of analogous products have been characterized for the solution photochemistry of disulfide-containing model peptides(18,20). In the solid state, the yields from insulin are ca.…”

The advantage of 7‐diethylamino‐3‐(4‐maleimidophenyl)‐4‐methylcoumarin fluorogenic tagging of sulfhydryl groups in oligopeptides for tandem mass spectrometry

“…Several photolysis experiments were carried out using lower (λ=253.7 nm) and/or higher (λ=280-300 nm) wavelengths to provide evidence for disproportionation mechanism of disulfide photolysis. [7] Due to the reactivity of free thiyl radicals and of sulfhydryl groups, instant and sensitive detection of disulfide splitting is still a challenge.Various methods and reagents have been reported in the literature for revealing free sulfhydryl moiety. Depending on the required detection limit, various thiol-reactive probes have been used for detection of sulfhydryl species, such as Ellman's reagent, [8] iodoacetamide-and maleimide-derivatives.…”