Rat pancreatic nucleoside diphosphate kinase, a novel regulator of cholecystokinin receptor affinity. Cloning and expression.

We previously demonstrated that the existence of two affinity states of the pancreatic cholecystokinin (CCK) receptor depends on the presence of ATP.' Subsequently, we established that the effect of ATP to induce two CCK binding affinity states was biochemically mediated by the enzyme nucleoside diphosphate kinase (NDPK) (manuscript in preparation). Nucleoside diphosphate kinase catalyzes the transfer of high energy gamma-phosphate groups from nucleoside triphosphates to nucleoside diphosphates. In that study the ability of an assortment of nucleoside triphosphates to serve as substrate for NDPK was compared with their ability to induce two binding affinity states of the CCK receptor on rat pancreatic membranes for which previous studies have observed only a single binding affinity state. Nucleoside triphosphates capable of serving as a substrate for NDPK could also induce two CCK binding affinity states on pancreatic membranes, whereas those that could not serve as substrate for NDPK could not induce two CCK binding affinity states. Furthermore, GDP potentiated the effect of ATP on binding (manuscript in preparation). To conclusively identify NDPK we found it necessary to clone and functionally express this enzyme. We report here that the characteristics of the cloned and expressed enzyme are similar to those of pancreatic membrane NDPK and consistent with the ability of this enzyme to induce two CCK binding affinity states.