Bound and purified alkaline phosphatase from rat duodenal and jejunal brush-border membranes: kinetics and magnesium stimulation.
Brush-border membranes from rat duodenal and jejunal mucosa were prepared by differential Ca(2+)-precipitation. Kinetical properties and Mg(2+)-stimulation of alkaline phosphatase were studied for the enzyme either bound to these membranes or purified from these membranes by liquid chromatography. With p-nitrophenylphosphate as substrate, the alkaline phosphatase apparent Km was lower in jejunum (90 microM) as compared with duodenum (160 microM), and lower for the purified enzyme (jejunum: 55 microM; duodenum: 97 microM) as compared to the bound one. In the presence of 5 mM MgCl2, the substrate affinity was in all cases decreased. For the bound enzyme Vmax was 10 times greater in duodenum compared to jejunum. 5 mM MgCl2 tripled the Vmax of the duodenal bound enzyme and increased it by 50% for the jejunal one, but a seven-fold increase was recorded for the purified enzyme at both levels of intestine. The apparent affinity for Mg2+ was similar for the bound and the free enzyme, for duodenum and for jejunum (Mg0.5: +/- 40 microM).
Gilles-Baillien
M
M
Laboratory of General and Comparative Biochemistry, University of Liège, Belgium.
Croux
E
E
D000469:Alkaline Phosphatase / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D004386:Duodenum / Q000201:enzymology; D007413:Intestinal Mucosa / Q000201:enzymology; D007583:Jejunum / Q000201:enzymology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008871:Microvilli / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains
D000469:Alkaline Phosphatase; D008274:Magnesium