Chemical Modification
Chemical treatment of wool fibre digests involves the stabilization of sulfhydryl groups to ensure reliable identification of keratins during mass spectrometry. In textile laboratories, alkylation prevents the cysteine residues that have been reduced from forming new disulfide crosslinks. This modification is usually achieved by adding iodoacetamide to the reduced protein solution under alkaline conditions.
The chemical alteration remains stable through subsequent purification steps, which enables reproducible trypsin digestion and precise peptide mass fingerprinting.
Reaction Mechanism
Covalent attachment of carbamidomethyl groups to the sulfur atoms of cysteine prevents oxidation during downstream processing. The reaction must proceed in the dark to avoid side reactions with amino acid side chains such as histidine or tyrosine. A thorough block of sulfhydryl groups ensures that the enzymatic cleavage with trypsin can proceed without steric hindrance.
Analytical Checkpoint
Validation of alkylation efficiency occurs during peptide mass mapping of raw wool blends. Quality control parameters require that at least ninety-eight percent of cysteine residues carry the carbamidomethyl modification. Incomplete reaction results in multiple peaks for the same peptide, complicating the quantitation of cashmere and sheep wool mixtures.
Process Limit
High concentrations of alkylating agents can cause non-specific reactions. The treatment stops being effective if the pH falls below seven. Excess reagent is neutralized to protect the column.
