ZX‐33118‐96 | Free Thiol Fluorometric Assay Kit 

Free thiols (–SH groups) play essential roles in biological systems and are critical for maintaining protein function and cellular redox balance. In particular, cysteine residues in proteins contain reactive thiol groups that can undergo reversible oxidative modifications, leading to the formation of disulfide bonds or other oxidized species. These modifications are known to regulate the activity, structure, and interactions of an increasing number of proteins. Accurate determination of free thiol content, especially within complex protein mixtures, remains a significant analytical challenge. This is particularly true under denaturing conditions, such as in the presence of chaotropic agents like guanidine hydrochloride, which are commonly used to unfold proteins and expose buried cysteine residues.

ZELLX® Free Thiol Assay Kit enables precise quantification of free thiols in a wide range of samples using a proprietary non-fluorescent substrate that reacts specifically with thiol groups to generate a highly fluorescent product. The assay is suitable for measuring thiols derived from low-molecular-weight compounds (e.g., glutathione generated in enzymatic reactions) as well as protein-bound cysteine residues. The assay has been validated in the presence of up to 2 M guanidine hydrochloride in the supplied assay buffer, allowing accurate determination of thiol content in denatured and unfolded proteins. This feature is particularly advantageous for studies requiring complete exposure of cysteine residues.

Although the kit includes a cysteine-based standard for quantification, it is recommended that users calibrate the assay using a standard that closely matches the chemical nature of the thiol being analyzed. For example, when measuring glutathione, calibration with a validated glutathione standard is advised to ensure optimal accuracy.

Technical Support: Customer satisfaction is very important to us. Please call us at +49(0)30 81309085 or send an email to technical[at]zellx.de with your technical questions. A member of our scientific staff will be glad to assist you.