Relationship of Na +K +-activated ATPase to fluid production by malpighian tubules of Locusta migratoria

The presence of a Na +K +-activated, Mg 2+-dependent ATPase (E.C. 3.6.1.3) has been demonstrated in microsomal preparations from the Malpighian tubules of Locusta. The effects of sodium and potassium ions, and different concentrations of ouabain, have been studied in relation to the activity of this enzyme and the ability of in vitro Malpighian tubule preparations to secrete fluid. From these studies it seems highly likely that a Na +K + activated ATPase ‘pump’ is involved in fluid transport across the walls of the tubules.