Rapid Microwave-Assisted Chemical Cleavage - Mass Spectrometric Method for the Identification of Hemoglobin Variants in Blood

A sensitive, rapid analytical method has been developed for the characterization of human hemoglobin disorders with very small volumes (<1 μL) of blood. As an alternative to conventional enzymatic digestion, a site-specific chemical cleavage method has been established using 0.05% formic acid under microwave-irradiation conditions for short time intervals, for example, less than 10 min. Peptide analysis was performed by MALDI TOF MS and capillary liquid chromatographic ESI MS/MS. The cleavage of the hemoglobin chains with formic acid occurred at either side or at both sides (C- and N-terminal) of aspartic acid residues, but preferentially N-terminally. The method has been applied to blood samples from hemoglobin S carrier heterozygotes and hemoglobin S thalassaemia compound heterozygotes with a reduced expression level of hemoglobin S. Both MALDI TOF MS and ESI MS/MS analysis allowed the identification of the hemoglobin S "signature" peptide. This alternative method of sample preparation is compatible with MS techniques and is expected to significantly contribute to the further development of rapid, robust, reproducible and sensitive analytical methods in proteomics and biomedical diagnostics where protein variant characterization is a crucial factor for biomarker discovery and disease identification.