Effect of bromoconduritol on glucosidase II from rat liver. A new kinetic model for the binding and hydrolysis of the substrate.
Bromoconduritol inhibits the p-nitrophenyl-glucosidase and maltase activities of glucosidase II purified from rat liver, an enzyme that removes the two alpha-1,3-linked glucose residues of the protein-bound oligosaccharide Glc2Man9GlcNAc2 in the processing of N-glycoproteins. The inactivation process exhibits pseudo-first-order kinetics. Previously, we have demonstrated the occurrence of two binding (active) sites in the glucosidase II for the substrates p-nitrophenyl alpha-D-glucopyranoside (pNphGlc) and maltose (high- and low-affinity sites). The inhibition kinetic studies with bromoconduritol indicate that the high- and low-affinity sites for pNphGlc correspond to high- and low-affinity sites for maltose, respectively. Bromoconduritol has no effect on the binding of the substrates (pNphGlc and maltose) to the high-affinity site, although it does modify the low-affinity site and hinders the binding of the two indicated substrates to this site. These results, together with previous reports, have prompted us to propose a new kinetic model of binding and hydrolysis of the physiological substrate of the enzyme, in which the outermost glucose residue would bind and be released at the high-affinity site, whereas the innermost glucose residue would do so at the low-affinity site.
Alonso
J M
JM
Departamento de Bioquímica y Biología Molecular, Universidad de León, Spain.
Santa-Cecilia
A
A
Calvo
P
P
D000818:Animals; D053138:Cyclohexenes; D065089:Glycoside Hydrolase Inhibitors; D006868:Hydrolysis; D007294:Inositol / Q000031:analogs & derivatives* / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008954:Models, Biological; D051381:Rats; D017208:Rats, Wistar; D000520:alpha-Glucosidases
D053138:Cyclohexenes; D065089:Glycoside Hydrolase Inhibitors; C036388:6-bromoconduritol; D007294:Inositol; C034251:4-nitrophenyl-alpha-glucosidase; D000520:alpha-Glucosidases