Isolation of the 12 S globulin from rapeseed (Brassica napus L.) and characterization as a "neutral" protein. On seed proteins. Part 13.

An isolation procedure for the 12 S rapeseed globulin is described which includes precipitation by dialysis, purification using gel chromatography on Sephadex G-200, and ion-exchange chromatography on DEAE-Sephadex A-50. The isolated globulin represents a neutral protein with an isoelectric point at pH 7.25--determined by isoelectric focusing--and a relation of the acidic to basic amino acid residues (epsilon Glu, Asp--Amide ammonia: epsilon Arg, Lys, His) of 1.0. As in other storage globulins high contents of glutamic (19%) and aspartic (10%) acid and a low content of sulphur containing amino acids are characteristic for the amino acid composition. Amongst the basic amino acids arginine has the highest percentage (7%). Opposite to results of other authors the sugar content of the globulin is low (0.5%). From the amino acid composition an average hydrophobicity according to Bigelow was calculated which amounts to be 1041 cal/res. (4.36 kJ/res.).