ADP-Ribosylation of Membrane Proteins in Cholinergic Nerve Terminals

Abstract
Lysed Torpedo synaptosomes or washed synaptosomal membranes were incubated with [32P]NAD+ and subjected to electrophoresis on sodium dodecyl sulfate polyacrylamide gels. More than 8 membrane proteins were ADP-ribosylated. The most intensely labeled proteins were those of MW = 62,000 and 82,000. Radiolabeling was more intense in synaptosomes than in other subcellular fractions. Cholera toxin caused ribosylation of additional synaptosomal proteins with MW = 42,000 and (in some preparations) 49,000. Neither endogenous nor cholera toxin-catalyzed ADP-ribosylation required added guanyl nucleotides. Cholera toxin increased the adenylate cyclase activity of synaptosomal membranes, suggesting that the cholera toxin substrates are regulatory components of adenylate cyclase in these synaptosomes.

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