(D-Ala, D-Leu) enkephalin reduces the binding of GTP in hippocampal membranes

The effect of (D-Ala, D-Leu) enkephalin (DADLE) on the binding of GTP in hippocampal preparations was studied. It was observed that treatment of hippocampal slices with 10(-5) -5 x 10(-5) M DADLE followed by the preparation of membrane fractions reduced the binding of 35S-GTP-gamma-S. There was no change in the affinity of the binding. This decrease of 35S-GTP-gamma-S binding was reversed when 5 x 10(-5) M naltrindole was included. The effect was not observed when the membrane fractions were incubated with DADLE. Photoaffinity labeling with the use of 32P P3-(4-azidoanilido)-P1 5'-GTP followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed the incorporation of radioactivity into molecular mass of the 43 kDa and 33-34 kDa proteins. 32P Photolabeling of both the 43 kDa and 33-34 kDa bands decreased following treatment of hippocampal slices with 10(-4) M DADLE. These results suggested that DADLE reduces the GDP-GTP exchange in hippocampal membranes.