RESUMO
OBJECTIVES: Characterization of beta-galactosidase in leukocytes and fibroblasts of heterozygotes for GM1 type I. DESIGN AND METHODS: Leukocyte and fibroblast beta-galactosidase activity was determined fluorimetrically using 4-methylumbelliferyl-beta-D-galactoside as an artificial substrate. Optimum pH, Km, Vmax and thermostability of the enzyme at 42 degrees C were determined. RESULTS: The leukocyte and fibroblast enzyme of heterozygotes have an optimum pH of 4.0 and 4.2, respectively. In normal subjects, the optimum pH was 4.2 in both cells, according to previous studies. The Km of the enzyme of heterozygotes was determined to be 0.65 mM in leukocytes and 0.59 mM in fibroblasts. The Vmax was determined in 167.21 nmol/h/mg of protein in heterozygotes leukocytes and 541.2 nmol/h/mg of protein in heterozygotes fibroblasts compared to 291.7 and 1768.1 nmol/h/mg of protein in controls leukocytes and fibroblasts, respectively. When leukocyte and fibroblast heterozygote beta-galactosidase was preincubated at 42 degrees C, after 80 min the residual activity was determined to be 25 to 30% of the initial activity. These results are similar to the control group. CONCLUSIONS: We have found significant differences between the two groups in some investigated parameters. Both fibroblasts and leukocytes showed a virtually similar level of reliability as source of enzyme for the detection of heterozygotes.
Assuntos
Gangliosidose GM1/enzimologia , Gangliosidose GM1/genética , Leucócitos/enzimologia , beta-Galactosidase/metabolismo , Células Cultivadas , Estabilidade Enzimática , Fibroblastos/enzimologia , Gangliosidose GM1/sangue , Triagem de Portadores Genéticos , Temperatura Alta , Humanos , Cinética , Valores de Referência , Pele/enzimologia , beta-Galactosidase/sangueRESUMO
OBJECTIVES: Some biochemical characteristics of the human leukocyte and fibroblast beta-galactosidase were studied. DESIGN AND METHODS: Leukocyte and fibroblast enzyme activity was determined fluorometricaly using 4-methylumbelliferyl-beta-D-galactoside as artificial substrate. Optimum pH, Km, Vmax and thermostability of the enzyme at 42 degrees 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 beta-galactosidase was pre-incubated at 42 degrees 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 beta-galactosidase performed on leukocytes and provided data for a better characterization of the enzyme beta-galactosidase, allowing the improvement of the analytical conditions.