aluminuminduced alterations in 3houabain binding and atp hydrolysis catalyzed by the rat brain synaptosomal nakatpase the nakatpase is responsible for maintenance of the ionic milieu of cells the objective of this study is to investigate the effect of aluminum an ion implicated in several neurological disorders on atp hydrolysis catalyzed by the rat brain synaptosomal nakatpase and on the binding of 3houabain to this enzyme alcl3 25100 microm inhibits the phosphatase activity of the nakatpase in a dosedependent manner alcl3 appears to act as a reversible noncompetitive inhibitor of nakatpase activity by decreasing the maximum velocity of the enzyme without significantly affecting the apparent dissociation constant with respect to atp alcl3 may affect mg2 sites on the nakatpase but does not appear to interact with na or k sites on the enzyme in contrast to this inhibitory effect on the phosphatase function of the enzyme alcl3 1100 microm stimulates the binding of 3houabain to the nakatpase this effect is due to an increase in the maximum 3houabain binding capacity of the enzyme with no change in the 3houabain binding affinity these data support the hypothesis that alcl3 may stabilize the phosphorylated form of the synaptosomal nakatpase which increases 3houabain binding while inhibiting the phosphatase activity of the enzyme