[GTP--a substrate for 3',5'-AMP-dependent phosphorylation of synaptic membrane proteins]

Using the method of electrophoresis in polyacrylamide gel (PAGE) it is shown that not only ATP, but GTP may play the role of phosphate donor for 3':5'-monophosphate (cAMP)-dependent phosphorylation. GTP is incorporated predominantly in the same "classic" 3':5'AMP-dependent phosphorylated proteins (with Mr 86 000, 82 000, 68 000, 61 000, 54 000) as that from ATP does. EGTA treatment of synaptic membranes enhances 3':5'-monophosphate (cAMP)-dependent phosphorylation with GTP used as a phosphate donor.