Further studies on the subunit structure and oligosaccharide moiety of human enterokinase

Highly purified human enterokinase was found by SDS-polyacrylamide gel electrophoresis to contain three heavily glycosylated subunits of apparent molecular masses 54 000, 102 000 and 140 000. The smallest subunit contained the active site serine residue and the oligosaccharide chains appear to be N-glycosidically linked as inferred from their stability to mild alkaline hydrolysis. Lectin affinity chromatography was used to separate sub-populations of the enzyme, the major one of which appeared to contain terminal alpha -linked N-acetyl galactosamine. Despite the presence of this sugar, no anti-A response was elicited in rabbits immunized with this sub-population. However, this sub-population did bind rabbit antibody directed against human blood group A substance, suggesting the presence of an "A-like" determinant. Studies with immobilized rabbit anti-human blood group A IgG suggest that there is no correlation between the blood group of an individual and the antigenic determinants on the enterokinase produced by the enterocytes of that individual. The study of the molecular properties of this important enzyme may give insights into pathological conditions with which it is linked.