Abstract
1. 1. Homogenates of gills from the freshwater shrimp M. amazonicum exhibit the following ATPase activities: (i) a basal, Mg 2+-dependent ATPase; (ii) an ouabain-sensitive, Na + + K +-stimulated ATPase; (iii) an ouabain-insensitive, Na +-stimulated ATPase; and (iv) an ouabain-insensitive, K +-stimulated ATPase. 2. 2. K + suppresses the Na +-stimulated ATPase activity in a mixed-type kind of inhibition, whereas Na + does not exert any noticeable effect on the K +-stimulated ATPase activity. 3. 3. The Na +- and the K +-stimulated ATPase activities are totally inhibited by 5 mM ethacrynic acid in the incubation medium. 4. 4. The Na +- and the K +-stimulated ATPase activities are not expressions of the activation of a Ca-ATPase. 5. 5. The possible localization and roles of the described ATPases within the gill epithelium are briefly discussed and evaluated.
Published Version
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