The protein is digested into peptide fragments by proteolytic enzymes.
The mixture is then subjected to paper electrophoresis followed by paper chromatography at 90° to the electrophoresis.
The resulting two-dimensional "fingerprint" reveals that normal hemoglobin HbA and sickle-cell HbS hemoglobin differ by a single peptide fragment.
Further analysis shows a single amino acid change:
valine is substituted for
at the 6th position of the beta chain.