Kinetic analysis of the interaction of alkyl glycosides with two human beta-glucosidases.
This paper addresses the similarities and differences in the topology of the catalytic centres of human liver cytosolic beta-glucosidase and placental lysosomal glucocerebrosidase, and utilizes well-documented reversible active-site-directed inhibitors. This comparative kinetic study was performed mainly to decipher the chemical and structural nature of the active site of the cytosolic beta-glucosidase, whose physiological function is unknown. Specifically, analysis of the effects of a family of alkyl beta-glucosides consistently displayed 100-250-fold lower inhibition constants with the cytosolic broad-specificity beta-glucosidase compared with the placental glucocerebrosidase; for example, with octyl beta-D-glucoside the Ki values were 10 microM and 1490 microM for the cytosolic and lysosomal beta-glucosidases respectively. Furthermore the higher affinity of the cytosolic beta-glucosidase than glucocerebrosidase for the amphipathic alkyl beta-D-glucosides was validated by the greater increase in the free energy of binding with increasing alkyl chain length [delta delta G0 (K,)/CH2: lysosomal enzyme, 2.01 kJ/mol (480 cal/mol); cytosolic enzyme, 3.05 kJ/mol (730 cal/mol)]. The implications of the presence of highly non-polar domains in the active site of the cytosolic beta-glucosidase are discussed with regard to its potential physiological substrates.
Gopalan
V
V
Department of Microbiology, University of Pittsburgh School of Medicine, PA 15261.
Daniels
L B
LB
Glew
R H
RH
Claeyssens
M
M
D001665:Binding Sites; D003600:Cytosol / Q000201:enzymology; D005959:Glucosidases / Q000037:antagonists & inhibitors*; D005962:Glucosylceramidase / Q000037:antagonists & inhibitors*; D006027:Glycosides / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D010718:Phosphatidylserines / Q000378:metabolism; D011609:Psychosine / Q000031:analogs & derivatives / Q000378:metabolism; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors*
D006027:Glycosides; D010718:Phosphatidylserines; D011609:Psychosine; C035742:sphingosyl beta-glucoside; D005959:Glucosidases; D001617:beta-Glucosidase; D005962:Glucosylceramidase