Practice question
Question
A peptide inert to Ellman’s test but reactive after β-mercaptoethanol contains:
Explanation
Ellman's reagent 5,5'-dithiobis-2-nitrobenzoic acid undergoes disulfide exchange only with free thiolate anions, generating chromophoric thionitrobenzoate measured at 412 nanometers absorbance. Peptide showing no reaction lacks accessible sulfhydryl groups. Treatment with β-mercaptoethanol reduces disulfide linkages to two free cysteine thiols, which now react strongly with Ellman's reagent giving yellow color. This differential reactivity proves original cysteines existed as oxidized disulfide bridge stabilizing tertiary structure, not as free thiol, tryptophan or histidine, important information for confirming oxidative folding in CD helical analysis and stability.
Related blogs
Guides and insights connected to this topic
SARS-CoV-2 Coronavirus: Structure, Genome, Proteins, Replication, Pathogenesis, and Host Interaction
Coronavirus Overview Coronaviruses (CoVs) are enveloped viruses (surrounded by a lipid membrane derived from host cells), belonging to the s...
Coronavirus Structure, Genome, Replication, Symptoms, Pathogenesis, and Prevention
Structure of Coronavirus Coronaviruses (enveloped RNA viruses) fall in the virus family Coronaviridae, order Nidovirales. They are enveloped...
Cucumber Mosaic Virus (CMV): Structure, Genome, Symptoms, Disease Cycle and Management
Cucumber Mosaic Virus (CMV): Introduction and Importance Cucumber Mosaic Virus (CMV) (plant-infecting RNA virus) is one of the most economic...