Identification of a Mg(2+)- and guanyl nucleotide-dependent glucagon receptor cycle by use of permeabilized canine hepatocytes.

摘要: We have investigated (by use of intact and saponinpermeabilized canine hepatocytes) the roles Mg2+ guanyl nucleotides in regulating glucagon-receptor interactions. In contrast to cells, hepatocytes bind [[125I]iodo-Tyr10]glucagon according a single first-order process exhibit apparent dissociation constant for glucagon binding during steady-state incubations. Further analysis permeabilized cell system demonstrated (a) temperature-sensitive action enhance extent affinity interactions at steady-state, (b) conversion Mg(2+)-independent hormone-receptor complexes Mg(2+)-dependent complexes, (c) effect inhibit specifically component interactions, (d) more rapid association with receptor incubations occurring presence or absence Mg2+, (e) ability induce both high low states Additional experiments identified an limit subsequent hormone, GDP, GTP, guanosine-5'-3-O-(thio)triphosphate (GTP gamma S) dissociate previously bound glucagon, specific requirement GDP re-activate additional cycles hormone binding. A model is presented which binds fashion, are converted state, nucleotide exchange initiates alteration context cell, G protein-mediated hydrolysis GTP required reinitialize system.