Remaury A, Ordener C, Shih J, Parini A
I.N.S.E.R.M. U.388 Pharmacologie Moléculaire et Physiopathologie rénale, Institut Louis Bugnard, C.H.U. Rangeuil, Toulouse, France.
Ann N Y Acad Sci. 1999 Jun 21;881:32-4. doi: 10.1111/j.1749-6632.1999.tb09338.x.
Biochemical and pharmacologic studies suggest that I2 imidazoline binding sites (I2BS) represent a heterogeneous family of membrane proteins. Indeed, the imidazoline binding sites located on monoamine oxidases (MAO) A and B display different pharmacologic properties. Recent results suggest that in liver and brain, I2BS may be located on proteins distinct from MAOs. The following observations indicate that in liver and brain, [3H]idazoxan binds exclusively to I2BS located on MAO-B: (1) size exclusion chromatography of digitonin-solubilized preparations from rabbit and human liver showed that [3H]idazoxan-specific binding eluted only in two peaks (approximately 175,000 and approximately 100,000 Da, corresponding to 90% and 10% of the recovered [3H]idazoxan binding) which also contained MAOs as determined by [14C]tyramine oxidation and Western blot analysis; (2) according to previous results obtained in various human and rat tissues, experiments performed in mice liver and brain showed that idazoxan was a potent inhibitor of [125I]-AZIPI photoincorporation to MAO-B but not to MAO-A; (3) in MAO-deficient transgenic mice, [3H]idazoxan binding to liver and brain membranes was completely abolished in MAO-B knockout mice and was not affected in MAO-A knockout mice. Together, these results show that in both liver and brain, I2BS are located exclusively on MAO-B. The imidazoline binding site on MAO-A, which photoincorporates [125I]-AZIPI and displays a low affinity for idazoxan, may not belong to the family of the I2 imidazoline binding sites.
生化和药理学研究表明，I2咪唑啉结合位点（I2BS）代表了一类异质性的膜蛋白家族。实际上，位于单胺氧化酶（MAO）A和B上的咪唑啉结合位点表现出不同的药理学特性。最近的研究结果表明，在肝脏和大脑中，I2BS可能位于与MAO不同的蛋白质上。以下观察结果表明，在肝脏和大脑中，[3H]伊达唑胺仅与位于MAO-B上的I2BS结合：（1）对来自兔和人肝脏的洋地黄皂苷增溶制剂进行尺寸排阻色谱分析表明，[3H]伊达唑胺特异性结合仅在两个峰中洗脱（约175,000和约100,000 Da，分别对应于回收的[3H]伊达唑胺结合的90%和10%），通过[14C]酪胺氧化和蛋白质免疫印迹分析确定这两个峰中也含有MAO；（2）根据先前在各种人和大鼠组织中获得的结果，在小鼠肝脏和大脑中进行的实验表明，伊达唑胺是[125I]-AZIPI光掺入MAO-B的有效抑制剂，但不是MAO-A的抑制剂；（3）在MAO缺陷的转基因小鼠中，[3H]伊达唑胺与肝脏和脑膜的结合在MAO-B基因敲除小鼠中完全消失，而在MAO-A基因敲除小鼠中不受影响。总之，这些结果表明，在肝脏和大脑中，I2BS仅位于MAO-B上。MAO-A上的咪唑啉结合位点可光掺入[125I]-AZIPI，且对伊达唑胺亲和力较低，可能不属于I2咪唑啉结合位点家族。
