[Isolation and characterization of an amatoxin-binding protein from wheat germ (author's transl)].

The preparation and characterization of a protein from wheat germ showing strong affinity to amatoxins (ABP) but differing from RNA polymerase B (II) is described. The purification, traced by [3H]amatoxin (O-methyldehydroxymethyl-alpha-amanitin), comprises 4 chromatographic steps, on Biogel A 1.5, DEAE-Sephadex, phosphocellulose, and again Biogel A 1.5. The protein exhibited in dodecyl sulfate polyacrylamide gel electrophoresis one single band with a molecular mass of 29,000 Da. Its isoelectric point is 4.9. The dissociation constant of the complex ABP-[3H]amatoxin is KD20 = 5 X 10(-7)M as determined by equilibrium dialysis against alpha-amanitin. By cyanogen bromide the protein is split into two fragments with molecular masses of 22,000 and 7,000 Da, respectively whose amino acid analyses, on summation, give the amino acid composition of ABP.