Characterization of β-hexosaminidase from liver and sera of diabetic patients and controls

β-Hexosaminidase activity is significantly elevated ( P < 0.005) in the sera from 27 diabetic patients when compared to 15 controls. Mixing studies indicate that this increased activity is not due to the presence of activators in diabetic sera or inhibitors in normal sera. It is indicated by kinetic analysis that diabetic and control sera β-hexosaminidases have comparable pH curves with broad optima centered around pH 4.5, comparable apparent Michaelis constants for 4-methylumbelliferyl-2-deoxy-2-acetamido-β- d-glucopyranoside (0.5–0.6 mm), comparable thermostability curves, and comparable isoelectric profiles with a major acidic isozyme at pI 4.8 to 4.9 (although diabetic sera may have increased amounts of an intermediate isozyme at pI 5.3 to 5.4). The activity levels and kinetic properties of β-hexosaminidase are comparable in liver supernatant fluids from diabetic patients and controls. Furthermore, the kinetic properties of the liver enzyme are very similar, if not identical, to those of the serum enzyme. By means of isoelectric focusing of β-hexosaminidase, comparable profiles for diabetic and control liver supernatant fluids with two forms with pI centered around 5.2 to 5.3 (Hex A) and 7.5 to 7.6 (Hex B) were obtained. However, increased relative amounts of Hex B appear to be present in diabetic livers: the average ratio of Hex B Hex A is 2.1 ± 0.1 for 3 diabetic livers and 1.0 ± 0.2 for 6 normal livers.