Properties of ATP-ase of the microvillus membrane isolated from epithelial cells of rabbit small intestine.

For the purpose to investigate the physiological functions of microvillus ATPase, general properties of the enzyme were studied on the microvillus membranes isolated from rabbit intestinal epithelial cells. 1) ATPase of the microvillus membranes was activated with Mg2+. Mg.ATP complex was thought to be a subStrate of the enzyme. The Michaelis constant for ATP of the ATPase was a value of 0.8 to I .0 mM. 2) The microvillus ATPase was also activated with Ca2+, but the affinity was lower than a half of that of Mg2+. 3) The optimum pH of the ATPase was about 7.8. 4) Activity of the microvillus ATPase was markedly inhibited by treating with deoxycholate (DOC), and the activity inhibited was partially restored by washing the microvillus membrane with distilled water. The structure of the membranes destroyed by treating with DOC was also partially restored by the same procedure. 5) Ultrasonic treatment also markedly destroyed the microvillus membrane and inhibited ATPase activity. Damaged ultrastructure and ATPase activity both were partially restored by treating with phospholipid, EPL. 6) Simultaneous presence of Na+ and K + stimulated scarcely the ATPase of purified microvillus membranes. 7) The microvillus ATPase was slightly activated in the presence of n-glucose. Phloridin gave little effect on the activity of the microvillus ATPase. ∗PMID: 4258663 [PubMed indexed for MEDLINE] Copyright c ©OKAYAMA UNIVERSITY MEDICAL SCHOOL Acta Med. Okayama 25, 13-28 (1970) PROPERTIES OF ATP-ASE OF THE MICROVILLUS MEMBRANE ISOLATED FROM EPITHELIAL CELLS OF RABBIT SMALL INTESTINE* Taibo YAMAMOTO**, Shuji SEKI, Seiichi HIRATA and Takuzo aDA Department of Biochemistry, Cancer Institute, Okayama University Medical School, Okayama, Japan (Director: Prof. T. Oda) Received for publication, December 10, 1970 The studies on the absorption mechanisms of sugars, amino acids and others in the small intestine have advanced extensively by using evertedsac system (1). WILSON et at. (2-4) and CRANE et at. (5-7) proved by using the everted-sac system that many kinds of sugars are actively transported through the small intestinal wall. They found that the absorption of D-glucose depends on sodium ion (Na+) inside the membrane, suggesting that the sugar-transport might be coupled with energy-dependent Na+ pumping (5-7). On the other hand, MILLER and CRANE (8) established the preparative method of brush borders of intestinal epithelial cells. They suggested that terminal digesting enzymes of sugar and peptide localized in the brush borders. aDA et at. (9, 10) purified microvillus membranes from the isolated microvillus borders by the method of ultrasonication and glycerol density gradient centrifugation, and found repeating particles (elementary particles), measuring approximately 60 A in diameter, on the surface of microvillm: membranes. They partially purified the elementary particles after solubilization with papain from the microvillus membranes, and suggested that the elementary particles coincide with or include an enzyme molecule such as disaccharidase and peptidase, which carries out terminal hydrolytic digestion of carbohydrates and proteins, respectively. They also indicated that Mg2+ -dependent ATPase and alkaline phosphatase localized in the microvillus membranes in relatively high concentrations were recovered in the papain-insoluble membraneous residue. The present communication describes g~neral properties of ATPase * This investigation was supported in part by research grants from the Ministry of Education, Japan. ** Present address: Department of Biology, Faculty of Science, Osaka University, Toyonaka, Osaka, Japan