Effect of deoxycholate on Ca 2+-ATPase of intestinal brush border membrane

Abstract

The effect of deoxycholate on the activity of intestinal brush border membrane Ca 2+-ATPase has been studied. The activity of Ca 2+-ATPase at 0.1 mM Ca 2+ was stimulated by deoxycholate ranging from 0.1 to 0.4 mM but at 1 mM Ca 2+ was depressed by the same concentrations of deoxycholate. A deoxycholate concentration exceeding 0.6 mM inhibited Ca 2+-ATPase at any concentration of Ca 2+. Deoxycholate affected the activity of Ca 2+-ATPase at lower concentrations than caused turbidity of Ca 2+-ATPase. It lowered the K m value of Ca 2+-ATPase for Ca 2+. An affinity component of Ca 2+-ATPase for ATP separated into low and high affinity components in the presence of deoxycholate. Sodium and potassium ions decreased Ca 2+-ATPase activity in the presence of deoxycholate. It is concluded that the ionic environment influences the effect of deoxycholate on Ca 2+-ATPase. These results suggest that the low dose of deoxycholate stimulates Ca 2+-ATPase by improving the accessibility of Ca 2+ to ATPase molecules but the high dose inhibits Ca 2+-ATPase by perturbing membrane lipid-ATPase interactions.