A Caveat When Using Alkyl Halides as Tagging Agents to Detect/Quantify Reactive Sulfur Species

Area of Science:

• Biochemistry
• Analytical Chemistry
• Chemical Biology

Background:

• Reactive sulfur species (RSSs), including hydrogen sulfide (H2S), polysulfides, and protein-bound sulfhydryls (protein-SSH), play critical roles in cellular signaling and redox homeostasis.
• Alkyl halides are commonly employed as derivatization agents to quantify RSSs, based on the assumption of a nucleophilic substitution reaction mechanism, analogous to thiol chemistry.

Purpose of the Study:

• To investigate the reaction mechanism between alkyl halides and reactive sulfur species (RSSs).
• To evaluate the accuracy of current methods for quantifying RSSs using alkyl halide tagging agents.

Main Methods:

• Exploration of the reaction pathways between various reactive sulfur species (H2S, polysulfides, protein-SSH) and representative alkyl halide tagging agents.
• Analysis of reaction products to identify competing reaction mechanisms beyond simple nucleophilic substitution.

Main Results:

• Reactive sulfur species (RSSs) were found to initiate a reductive dehalogenation reaction with alkyl halides, in addition to the presumed nucleophilic substitution.
• This reductive dehalogenation pathway leads to the formation of reduced, unloaded tag molecules and oxidized RSS, indicating a deviation from expected reaction stoichiometry.

Conclusions:

• The established method of using alkyl halides to quantify RSSs may lead to underestimation of their actual concentrations in biological samples.
• The precise speciation of RSSs might also be compromised due to the competing reductive dehalogenation pathway, necessitating further investigation and method refinement.