INTERACTION OF [3H]AMP WITH LIVER-CELLS AND THEIR PLASMA-MEMBRANES

The specific binding of [H-3]AMP to hepatocytes and their plasma membranes was studied. The phasic nature of this interaction was demonstrated; the maximum binding of [H-3]AMP was recorded during the first 15 sec. An analysis of the equilibrium binding in Scatchard plots showed the presence of one class of binding sites with dissociation constant equal to 20-mu-M, both for hepatocytes and for plasma membranes. The [H-3]AMP-binding sites were inactivated with trypsin and by heating. 5'-Phosphorylated compounds of adenosine (ATP, ADP) effectively replaced [H-3]AMP, whereas adenosine, beta-glycerophosphate, and 3'-AMP did not have a competitive effect. In the presence of an inhibitor of 5'-nucleotidase - concanavalin A - the binding of [H-3]AMP was increased by 400%. It was suggested that the catalytic site of 5'-nucleotidase may be a receptor for adenine nucleotides.