THE CARBOXYL-TERMINAL HALF-MOLECULE OF OVOTRANSFERRIN PREPARED BY SELECTIVE DIGESTION OF THE AMINO-TERMINAL LOBE WITH THERMOLYSIN

Diferric ovotransferrin was hydrolyzed by thermolysin, a thermostable protease, at elevated temperatures. At 65-degrees-C, the amino(N)-terminal lobe was completely digested into small peptides, while the carboxyl(C)-terminal lobe was significantly resistant to the protease. This permitted the isolation of an iron-bound C-terminal half-molecule consisting of a glycosylated single polypeptide in an excellent yield (about 90%). The fragment comprises the residues from 336 to the C-terminus of ovotransferrin. The results for the visible absorption spectrum of the copper-bound fragment, the stability of the iron-bound fragment in high concentration of urea, and the CD spectra of the fragment in the far and near UV regions indicated that it retains the metal binding activity and conformation of the C-terminal lobe of intact ovotransferrin.