Proteolytic Conversion of the Molecular Forms of Bovine Milk Galactosyltransferase

Tryptic hydrolysis of galactosyltransferase purified from bovine milk by affinity chromatography resulted in a decrease in the amount of the high molecular weight form (58,000) with a concomitant increase in the amount of lower molecular weight form (42,000) with little loss of activity. After extensive activity loss, a peptide of molecular weight 38,000 remained as the predominant species and retained poorly the capacity to bind substrate and α-lactalbumin. Trypsinolysis produced at least one small peptide fragment which migrated with the tracking dye on sodium dodecyl sulfate gels. Chymotryptic hydrolysis led to a loss in enzymic activity and gave rise to at least five peptides ranging from 10,000 to 32,000 in molecular weight. As with trypsin treatment, only the larger fragments (molecular weight g 25,000) contained carbohydrate.