Inhibition of alkaline phosphatase activity by glucose.

Non-enzymatic glycosylation (NEG) of alkaline phosphatase (AP) was studied after short- and long-term incubation with glucose and other carbohydrates. Glucose and amino sugars clearly inhibited the enzyme activity; this was in contrast to reducing and non-reducing disaccharides, which had an enhancing effect. After AP had been incubated with 18 nmol/l glucose for 180 minutes (short-term incubation), a subsequent extensive dialysis revealed full recovery of the enzymatic activity.

Reduced susceptibility of glycosylated hemoglobin to proteolytic cleavage.

Four different experimental designs were selected to study, whether glycosylation of hemoglobin alters susceptibility against proteolytic degradation. We compared the resistance of different hemoglobin fractions against degradation by pure proteolytic enzymes, by liver cell culture, by live organ culture and the resistance of in vitro glycosylated vs. "non-glycosylated" hemoglobin solutions.

Proteolytic degradation of the glomerular basement membrane and immunochemical characterization of split products.

Glomerular basement membranes (GBM) were isolated and subjected to enzymatic degradation with the protease trypsin (Serva), chymotrypsin (Serva), papain (Sigma), pepsin (Serva) and collagenase (Worthington) as well as a lysosomal preparation from glass adherent rat blood and peritoneal exudate cells. Split products were characterized by immunoelectrophoresis and cellulose acetate electrophoresis. Urine was obtained from healthy rats and rats with Masugi's experimental glomerulonephritis, dialyzed and concentrated and applied on immunoelectrophoresis, using anti-GBM antibody from rabbit.