CHARACTERIZATION OF [H-3]IDAZOXAN BINDING-PROTEINS IN SOLUBILIZED MEMBRANES FROM RABBIT AND HUMAN LIVER

Several studies have shown that I-2 imidazoline binding sites are loca lized on monoamine oxidases. Recent results obtained after solubilizat ion of rat brain membranes and analysis by size-exclusion chromatograp hy suggested the existence of additional I-2 imidazoline binding sites located on proteins distinct from monoamine oxidases. In order to def ine whether such binding sites are expressed in human and rabbit liver , we solubilized I-2 imidazoline binding sites and monoamine oxidases and compared their elution profile by size-exclusion chromatography. I -2 binding sites were labeled using [H-3]idazoxan. Monoamine oxidases were identified by the measure of [C-14]tyramine oxidation and Western blot analysis using an anti-MAO-A/MAO-B polyclonal antiserum. After s olubilization of rabbit or human liver using 1% digitonin, 90% of [H-3 ]idazoxan binding eluted in a major peak corresponding to a M-r of sim ilar to 175000 Da. A minor peak, (M-r similar to 100000 Da) representi ng 10% of the recovered [H-3]idazoxan binding, was also observed. [C-1 4]tyramine oxidation as well as immunoreactive bands corresponding to MAOs were exclusively detected in fractions containing [H-3]idazoxan b inding. These results show that solubilized I-2 imidazoline binding si tes distinct from monoamine oxidases are not detectable in rabbit and human liver. (C) 1998 Published by Elsevier Science B.V. All rights re served.