Biochemical characterization of brown adipose tissue beta-adrenergic receptor

The beta-adrenergic receptor of rodent brown fat plays a key role in the control of energy dissipation by this tissue. The aim of the present study was to further characterize the biochemical properties of this receptor. The beta-receptor of rat interscapular brown adipose tissue plasma membranes was found to bind the beta-adrenergic antagonist [125I]cyanopindolol with a high affinity (KD 67 pM). The [125I]cyanopindolol receptor complex could be solubilized by digitonin and the isoelectric point of the solubilized receptor was found to be 5.8. Brown adipose tissue plasma membranes were labeled with the photoaffinity ligand [125I] cyanopindolol diazirine and labeled membrane proteins were separated by sodium dodecylsulfate polyacrylamide gel electrophoresis and analyzed by autoradiography. Autoradiograms revealed a peptide of 62 kDa whose labeling was stereoselectively displaced by alprenolol and isoproterenol. The beta 1-selective antagonist betaxolol was about 100 times more potent in displacing the labeling of this 62 kDa peptide than the beta 2-selective antagonist ICI 118,551. Based upon these data, it appears that the beta-receptor in brown adipose tissue is a beta 1 subtype with molecular weight of 62 kDa.