Crambin displays amino acid heterogeneity at positions 22 (Pro or Ser) and 25 (Leu or Ile). Using reversed phase HPLC the crambin mixture can be resolved into two protein fractions. It is shown by amino acid analysis and NMR spectroscopy that these fractions represent single proteins (Ser-22/Ile-25 and Pro-22/ Leu-25 species). A first characterization of the 1H-NMR spectra of these species is presented.
