Comparison of the Size and Rate of Formation of Peptides Released by Limited Proteolysis of .beta.-Lactoglobulins A and B with Immobilized Trypsin

Proteolytic susceptibility of β-lactoglobulin (β-Lg) genetic variants A and B was determined by subjection to immobilized trypsin. Products of limited proteolysis, performed in 50 mM Tris-HCl buffer (pH 8.0) at 4 o C, were characterized by fractionation with anion-exchange chromatography and by denaturing gel electrophoresis of the isolated fractions. Both the rate of appearance of products and the peptides formed were different for the two variants. Two major peptides, with estimated molecular weights of 7500 and 8200 were obtained in homogeneous form by ion-exchange fractionation of β-Lg A hydrolysates. Similar fractionation of β-Lg B hydrolysates yielded fractions that were heterogeneous, containing larger peptides that were not present in β-Lg A hydrolysates