PURIFICATION AND BIOCHEMICAL-CHARACTERIZATION OF TEPARY BEAN (PHASEOLUS-ACUTIFOLIUS) MAJOR GLOBULIN

Tepary bean (Phaseolus acutifolius var. lactifolius) major storage glo bulin (>90% purity by electrophoresis) was composed of three glycosyla ted polypeptides with estimated molecular weights of 49 500, 45 890, a nd 44 510. The protein had an absorption maximum at 278 nm and an A(28 0 nm) (1%) of 6.61 in 20 mM Tris-HCl pH 8.1 containing 0.5 M NaCl. The carbohydrate content of the protein was 8.23% (w/w). The hydrodynamic radius (Stokes' radius) of the native protein was 53.3 Angstrom. Amin o acid composition of the globulin indicated that S-containing amino a cids were the first limiting amino acids. Acidic, basic, uncharged pol ar, and hydrophobic amino acids accounted for 28.75, 12.42, 21.94, and 36.91% (by weight), respectively of the total protein. The native glo bulin was resistant to in-vitro proteolysis. Heat denaturation (100 de grees C, 30 min) of the globulin in aqueous 0.5 M NaCl did not improve the in-vitro proteolysis of the globulin. Heat denaturation (100 degr ees C, 30 min) of the globulin in the digestion buffer in the absence of NaCl facilitated complete in-vitro proteolysis of the globulin by c hymotrypsin, trypsin, and pepsin.