title: Ca2+-dependent ATP hydrolysis of the porcine intestinal brush-border membranes.
abstract: The brush-border membrane from the porcine small intestine possesses Ca2+-dependent ATPase activity. The Ca2+ stimulation of ATP hydrolysis by the membranes is biphasic with a high affinity (Km = 0.38 microM) and a low affinity (Km = 98.3 microM). Treatment of the membrane vesicles with n-heptylthioglucoside did not cause further increase of the Ca2+-ATPase activity. Mg2+ also stimulates the ATP hydrolysis in the absence of Ca2+ but decreases the Ca2+-ATPase activities at 0.59 and 200 microM free Ca2+. The Ca2+-ATPase activities are not inhibited by addition of vanadate, ouabain, sodium azide and alkaline phosphatase inhibitors (theophylline and L-phenylalanine), irrespective of the Ca2+ concentrations in medium. A specific calmodulin-inhibitor W-7 (up to 30 microM) also did not influence on the Ca2+-ATPase activities at 0.59 and 200 microM free Ca2+. The Ca2+-ATPase activities at 0.59 and 200 microM free Ca2+ show no specificity for ATP. ADP, GTP and CTP could also be used as substrates. From these results, it is suggested that the porcine intestinal brush-border membrane possesses Mg2+-independent Ca2+-ATPase activity and that the Ca2+-ATPase activities with biphasic responses for Ca2+ stimulation observed in the present study reside on the same protein. The physiological functions of the Ca2+-ATPase in the membranes, however, remain unknown at present.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors; D000818:Animals; D001386:Azides / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D007421:Intestine, Small / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008871:Microvilli / Q000201:enzymology; D009711:Nucleotides / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D019810:Sodium Azide; D013379:Substrate Specificity; D013552:Swine; D013865:Thioglycosides / Q000494:pharmacology; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D001386:Azides; D002147:Calmodulin; D009711:Nucleotides; D013865:Thioglycosides; D014639:Vanadium; D014638:Vanadates; D010042:Ouabain; C046542:heptyl 1-thioglucoside; D000255:Adenosine Triphosphate; D019810:Sodium Azide; D000469:Alkaline Phosphatase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium