Kinetic properties of neutral alpha-glucosidase in the atrophic mucosa of self-emptying blind loops of rat jejunum: a microdensitometric study at two different villus sites.
The in situ kinetic constants of neutral alpha- glucosidase were determined in the atrophic jejunal mucosa of self-emptying blind loops and in corresponding jejunal segments of control rats, using a quantitative histochemical technique. The apparent maximum velosity (Vmax) and km values were calculated from absorbance measurements of an azo dye-deposit formed in the brush border membrane at the villus base and at the transition zone between the middle and upper one-third of the villus. In the controls a significant increase of apparent Vmax and substrate affinity (decrease of apparent Km) was obtained, corresponding to enterocyte maturation along the villi. The mucosal atrophy in self-emptying blind loops was accompanied by a significant decrease of apparent Vmax of neutral alpha-glucosidase at both representative villus sites, but the substrate affinity was increased at both sites. The results indicate that alpha-glucosidase activity was reduced when measured at the cellular level of two representative villus sites in the atrophic jejunal mucosa, possibly due to the absence of substrate-effected enzyme induction. The decrease on hydrolytic enzyme activity was not matched by a compensatory increase in substrate affinity.
D000818:Animals; D001284:Atrophy; D002462:Cell Membrane / Q000201:enzymology*; D005260:Female; D005959:Glucosidases / Q000378:metabolism*; D006651:Histocytochemistry; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000473:pathology; D007583:Jejunum / Q000201:enzymology* / Q000473:pathology; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D000520:alpha-Glucosidases / Q000378:metabolism*
D005959:Glucosidases; D000520:alpha-Glucosidases