Abnormal glycosylation of duodenal membranous alkaline phosphatase induced by cysteamine in rats.
The membranous and soluble isoenzymes of alkaline phosphatase (AP-ase) were isolated from the duodenal mucosal cells in control and cysteamine-treated rats. Both the cytosolic and membranous isoenzymes of the AP-ase were drastically inhibited by a single subcutaneous injection of cysteamine-HCl, a potent duodenal ulcerogen. However, cysteamine did not change the isoenzyme distribution between the two compartments of the duodenal mucosal cells. Membranous isoenzyme of duodenal AP-ase in control rats was separated by concanavalin A (Con A) affinity chromatography into three fractions: unbound (65%), weakly bound (11%) and strongly bound (24%). The strongly bound fraction disappeared completely from duodenal mucosal cells of cysteamine-treated rats before any visible signs of ulcer formation. Since the strongly bound fraction of AP-ase contains high mannose-type sugar chains, we concluded that the ulcerogen affected the initial mannosylation (or glypiation) of membranous AP-ase which took place in the rough endoplasmic reticulum of the mucosal cells. In control rats, the Con A fractions of the membranous AP-ase were separated by gel filtration as tetramers of M(r) 420 and 340 kD and dimers of M(r) 185-200 kD. In cysteamine-treated rats, neither the strongly bound tetramers of 340 kD nor dimers of 185 kD were found by gel filtration. However, cysteamine did not change the total tetramer: dimer ratio. Judging by the decrease of Vmax values at the pH optimum, the different molecular forms of the AP-ase are selectively sensitive to cysteamine inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Japundzic
I
I
Institute of Biochemistry, Faculty of Medicine, Belgrade, Yugoslavia.
Kosaric
B
B
D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D003543:Cysteamine / Q000494:pharmacology*; D004386:Duodenum / Q000201:enzymology*; D005260:Female; D006031:Glycosylation; D007413:Intestinal Mucosa / Q000201:enzymology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008970:Molecular Weight; D051381:Rats; D017208:Rats, Wistar
D007527:Isoenzymes; D003543:Cysteamine; D000469:Alkaline Phosphatase