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.