[Immunochemical study of the degradation of circulating glycoproteins and the neurospecific membrane glycoprotein D2 by cathepsin D of the human brain].

Cathepsin D was isolated from human brain. A consecutive use of affinity chromatography on hemoglobin-sepharose 4B and column chromatography on hydroxylapatite resulted in a homogeneous enzyme (as was demonstrated by SDS polyacrylamide gel electrophoresis) with a molecular weight of about 48,000, 2800-fold purification and 3.4% yield. Incubation of serum proteins in the presence of purified cathepsin D resulted in a gradual decrease of immunoreactive forms of albumin, orosomucoid, transferrin, and other alpha 1, alpha 2 and beta-globulins. The degradation was revealed by crossed immunoelectrophoresis. Crossed affinity immunoelectrophoresis in the presence of ConA showed specific degradation of serum glycoproteins. Rocket immunoelectrophoresis with monospecific antisera raised against human adult brain glycoprotein D2 revealed a rapid and linear degradation of detergent-solubilized and partially purified human membrane glycoprotein D2 by purified cathepsin D. Incubation of glycoprotein D2 in the presence of cathepsin D (30 min, 37 degrees C) resulted in degradation of 95% of specific protein. An exposure of human brain membrane fragments to cathepsin D resulted in linear degradation of membrane-bound glycoprotein followed by an appearance of a soluble immunoreactive form of protein D2.