Biochemical studies on leukocyte and fibroblast human β-galactosidase

Objectives: Some biochemical characteristics of the human leukocyte and fibroblast β-galactosidase were studied. Design and Methods: Leukocyte and fibroblast enzyme activity was determined fluorometricaly using 4-methylumbelliferyl-β-D-galactoside as artificial substrate. Optimum pH, Km, Vmax and thermostability of the enzyme at 42 °C were determined. Results: The leukocyte and fibroblast enzyme has an optimum pH at 4.2, which is in agreement with the lysosomal origin of the enzyme. The Km of the enzyme was 0.62 in leukocytes and 0.67 in fibroblasts, and Vmax was 289.9 nmol/h/mg of protein and 1779.2 nmol/h/mg of protein in the two tissues, respectively. When fibroblast or leukocyte β-galactosidase was pre-incubated at 42 °C, it did not retain its activity because the residual activity after 80 minutes of pre-incubation at this temperature was lower than 30% of the initial activity both in leukocytes and fibroblasts. Conclusions: This was the first study of Km, Vmax and thermostability of β-galactosidase performed on leukocytes and provided data for a better characterization of the enzyme β-galactosidase, allowing the improvement of the analytical conditions.