Formation of the high-affinity agonist state of the alpha 1-adrenergic receptor at cold temperatures does not require a G-protein.
Two methods were employed to uncouple hepatic alpha 1-adrenergic receptors from their associated G-protein (termed Gp) in order to determine whether locking of the alpha 1-receptor in a high-affinity agonist state at cold temperatures (2 degrees C) represents formation of a ternary complex. Uncoupling is defined as the inability to observe the GppNHp-sensitive, high-affinity agonist state of the receptor in [3H]prazosin competition binding studies performed at 25 degrees C. The first method for achieving uncoupling involved brief alkalinization and resulted in greater than 95% loss of several G-proteins. The second method involved proteolytic cleavage of either part or all of the alpha 1-receptor coupling domain from the binding domain. Following either treatment, receptors were converted to the high-affinity agonist state at 2 degrees C. Thus, while formation of the high-affinity state of the receptor at higher temperatures may require Gp, formation of this state at 2 degrees C does not require Gp or even the entire alpha 1-adrenergic receptor.
Lynch
C J
CJ
Howard Hughes Medical Institute, Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232.
Taylor
S J
SJ
Smith
J A
JA
Exton
J H
JH
D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D003080:Cold Temperature; D004837:Epinephrine / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D011224:Prazosin / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D011224:Prazosin; D004837:Epinephrine