Divalent cation, ATP-dependent [3H]leu-enkephalin uptake by synaptic vesicle fraction isolated from bovine caudate...

The mechanism of [3H]Leu-enkephalin uptake into synaptic vesicle fraction from bovine caudate nucleus was investigated. The simultaneous addition of 2 mM MgCl2, 2 mM CaCl2, and 2 mM ATP stimulated the uptake 22 times over the control, whereas the separate addition of these agents augmented the uptake 2.4 times at most. The addition of 2 mM MGCl2 plus 2 mM ATP and of 2 mM CaCl2 plus 2 mM ATP increased the uptake 6.6 times and 4.5 times, respectively. The cation, ATP-dependent uptake reached its half-maximal level within 10 min after the initiation of incubation at 25 degrees C, and little Leu-enkephalin was taken up at 0 degree C. The apparent Km for the uptake of [3H]Leu-enkephalin was 1.8 x 10(-7) M. Guanosine triphosphate stimulated the uptake as well as ATP, whereas CTP and ITP were only one-fourth effective of ATP. The cation, ATP-dependent uptake was inhibited by 25% and 20% in the presence of 0.1 mM colchicine and 1 microM reserpine, respectively.