EFFECT OF BROMOCONDURITOL ON GLUCOSIDASE-II FROM RAT-LIVER - A NEW KINETIC-MODEL FOR THE BINDING AND HYDROLYSIS OF THE SUBSTRATE

Citation
Jm. Alonso et al., EFFECT OF BROMOCONDURITOL ON GLUCOSIDASE-II FROM RAT-LIVER - A NEW KINETIC-MODEL FOR THE BINDING AND HYDROLYSIS OF THE SUBSTRATE, European journal of biochemistry, 215(1), 1993, pp. 37-42
Citations number
16
Categorie Soggetti
Biology
ISSN journal
00142956
Volume
215
Issue
1
Year of publication
1993
Pages
37 - 42
Database
ISI
SICI code
0014-2956(1993)215:1<37:EOBOGF>2.0.ZU;2-S
Abstract
Bromoconduritol inhibits the p-nitrophenyl-glucosidase and maltase act ivities of glucosidase II purified from rat liver, an enzyme that remo ves the two alpha-1,3-linked glucose residues of the protein-bound oli gosaccharide Glc2Man9GlcNAc2 in the processing of N-glycoproteins. The inactivation process exhibits pseudo-first-order kinetics. Previously , we have demonstrated the ocurrence of two binding (active) sites in the glucosidase II for the substrates p-nitrophenyl alpha-D-glucopyran oside (pNphGlc) and maltose (high- and low-affinity sites). The inhibi tion kinetic studies with bromo-conduritol indicate that the high- and low-affinity sites for pNphGlc correspond to high- and low-affinity s ites for maltose, respectively. Bromoconduritol has no effect on the b inding of the substrates (pNphGlc and maltose) to the high-affinity si te, although it does modify the low-affinity site and hinders the bind ing of the two indicated substrates to this site. These results, toget her with previous reports, have prompted us to propose a new kinetic m odel of binding and hydrolysis of the physiological substrate of the e nzyme, in which the outermost glucose residue would bind and be releas ed at the high-affinity site, whereas the innermost glucose residue wo uld do so at the low-affinity site.