Biochemical studies on leukocyte and fibroblast human beta-galactosidase.
OBJECTIVE
Some biochemical characteristics of the human leukocyte and fibroblast beta-galactosidase were studied.


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.
Coelho
J C
JC
Department of Biochemistry, Federal University of Rio Grande do Sul, University Hospital of Porto Alegre, Brazil. pires@portoweb.com.br
Sopelsa
A M
AM
Tobo
P R
PR
Severini
M H
MH
Silva
C D
CD
Giugliani
R
R
D005347:Fibroblasts / Q000201:enzymology; D016537:Gangliosidosis, GM1 / Q000097:blood / Q000201:enzymology; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007962:Leukocytes / Q000201:enzymology*; D001616:beta-Galactosidase / Q000097:blood / Q000378:metabolism*
D001616:beta-Galactosidase