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, K m, V max 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 K m of the enzyme was 0.62 in leukocytes and 0.67 in fibroblasts, and V max 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 K m, V max 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.