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
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.