Stimulation of intestinal Ca2+-ATPase activity by cysteine.

Cysteine stimulated the activity of the ATPase dependent on Ca²⁺, but not Mg²⁺ and Zn²⁺, in the microsomal and brush border fractions of rat duodenal mucosa. This ATPase was localized in the duodenum but was not present in the jejunum of ileum. Kinetic studies showed that cysteine did not change the K_m value for ATP but decreased that for Ca²⁺. Other sulfhydryl-containing reagents, such as glutathione, 2-mercaptoethanol and dithiothreitol, also stimulated the Ca²⁺-ATPase activity. These findings suggest that thiol-containing reagents stimulate the Ca²⁺-ATPase activity in the duodenum by affecting the interaction of the enzyme with Ca²⁺.