Remaury A, Raddatz R, Ordener C, Savic S, Shih J C, Chen K, Seif I, De Maeyer E, Lanier S M, Parini A
Institut National de la Sante et de la Recherche Medicale, Pharmacologie Moléculaire et Physiopathologie Rénale, Institut Louis Bugnard, Centre Hospitalier Universitaire Rangeuil, Toulouse, France.
Mol Pharmacol. 2000 Nov;58(5):1085-90. doi: 10.1124/mol.58.5.1085.
The I(2) subgroup of imidazoline-binding sites was identified as monoamine oxidases (MAOs), but it is unclear whether there are I(2)-binding sites located on proteins distinct from MAOs. To address this issue, we characterized I(2)-binding proteins in liver and brain of wild-type and MAO A- and MAO B-deficient mice. I(2)-binding sites were identified using [(3)H]idazoxan and the photoaffinity adduct 2-[3-azido-4-[(125)I]iodophenoxyl]methylimidazoline ([(125)I]AZIPI). [(3)H]Idazoxan labeled binding sites with ligand recognition properties typical of I(2) sites in both brain and liver of wild-type mice. High-affinity, specific [(3)H]idazoxan binding were not altered in MAO A knockout (KO) mice. In contrast, [(3)H]idazoxan binding was completely abolished in both liver and brain of MAO B KO mice. In wild-type mice, [(125)I]AZIPI photolabeled three proteins with apparent molecular masses of approximately 28 (liver), approximately 61 (brain), and approximately 55 kDa (liver and brain). The photolabeling of each protein was blocked by the imidazoline cirazoline (10 microM). Photolabeling of the approximately 61- and approximately 55-kDa proteins was not observed in MAO A and B KO mice, respectively. In contrast, photolabeling of the liver approximately 28-kDa protein was still observed in MAO-deficient mice, indicating that this protein is unrelated to MAOs. These data indicate that I(2) imidazoline-binding sites identified by [(3)H]idazoxan reside solely on MAO B. The binding sites on MAO A and the liver approximately 28-kDa protein may represent additional subtypes of the family of the imidazoline-binding sites.
咪唑啉结合位点的I(2)亚组被鉴定为单胺氧化酶（MAOs），但尚不清楚是否存在位于与MAOs不同的蛋白质上的I(2)结合位点。为了解决这个问题，我们对野生型、MAO A缺陷型和MAO B缺陷型小鼠的肝脏和大脑中的I(2)结合蛋白进行了表征。使用[(3)H]异喹唑啉和光亲和加合物2-[3-叠氮基-4-[(125)I]碘苯氧基]甲基咪唑啉([(125)I]AZIPI)鉴定I(2)结合位点。[(3)H]异喹唑啉在野生型小鼠的大脑和肝脏中标记了具有I(2)位点典型配体识别特性的结合位点。在MAO A基因敲除（KO）小鼠中，高亲和力、特异性的[(3)H]异喹唑啉结合未改变。相比之下，在MAO B KO小鼠的肝脏和大脑中，[(3)H]异喹唑啉结合完全消失。在野生型小鼠中，[(125)I]AZIPI光标记了三种蛋白质，其表观分子量分别约为28 kDa（肝脏）、约61 kDa（大脑）和约55 kDa（肝脏和大脑）。每种蛋白质的光标记都被咪唑啉西拉唑啉（10 microM）阻断。在MAO A和B KO小鼠中分别未观察到约61 kDa和约55 kDa蛋白质的光标记。相反，在MAO缺陷型小鼠中仍观察到肝脏约28 kDa蛋白质的光标记，表明该蛋白质与MAOs无关。这些数据表明，由[(3)H]异喹唑啉鉴定的I(2)咪唑啉结合位点仅存在于MAO B上。MAO A上的结合位点和肝脏约28 kDa蛋白质可能代表咪唑啉结合位点家族的其他亚型。
