Raddatz R, Lanier S M
Department of Cell and Molecular Pharmacology and Experimental Therapeutics, Medical University of South Carolina, Charleston, USA.
Neurochem Int. 1997 Jan;30(1):109-17. doi: 10.1016/s0197-0186(96)00036-8.
Imidazoline binding sites or imidazoline/guanidinium receptive sites (IGRS) recognize bioactive endogenous substances and a variety of pharmacologically active compounds containing imidazoline or guanidinium moieties. The family of imidazoline binding proteins consists of multiple membrane-associated proteins that differ in their tissue/subcellular localization, M(r) and ligand recognition properties. Two of the imidazoline binding proteins are identical to the mitochondrial enzyme monoamine oxidase (MAO) A and B isoforms, which contain imidazoline binding domains distinct from the enzyme active site. The relationship between the imidazoline binding proteins and monoamine oxidases was further characterized in the present report using a covalent probe (2-[3-azido-4[125I]iodophenoxy] methyl imidazoline, [125I]-AZIPI) to label the imidazoline binding proteins in different species and following transient expression of MAO- A and -B in COS 7 cells. Species homologues of MAO-A and -B in rat and human differ in their apparent molecular weight by approximately 2000 Da. In rat and human liver [125I]-AZIPI identified peptides with apparent molecular weights similar to those of the species homologues of MAO. Peptides of M(r) approximately 63,000 (MAO-A) and approximately 59,000 (MAO-B) were also photolabeled in membranes prepared from COS-7 cells transfected with human cDNA clones encoding MAO-A or -B. Additional experiments indicate that the imidazoline binding domains on MAO-A and -B exhibit different ligand recognition properties. The covalent labeling of human liver MAO-B was more sensitive than that of placenta MAO-A to inhibition by the imidazoline 2-(4,5-dihydroimidaz-2-yl)-quinoline (BU224). These data indicate that the A and B isoforms of MAO possess imidazoline binding domains that differ in their ligand recognition properties. Allosteric regulation of the activity of MAO via the imidazoline binding domains may be of significance in various disease states associated with elevated enzyme expression or in which the enzyme is a therapeutic target.
咪唑啉结合位点或咪唑啉/胍盐受体位点（IGRS）可识别生物活性内源性物质以及多种含有咪唑啉或胍盐部分的药理活性化合物。咪唑啉结合蛋白家族由多种膜相关蛋白组成，它们在组织/亚细胞定位、分子量（M(r)）和配体识别特性方面存在差异。其中两种咪唑啉结合蛋白与线粒体酶单胺氧化酶（MAO）A和B同工型相同，它们含有与酶活性位点不同的咪唑啉结合结构域。在本报告中，使用共价探针（2-[3-叠氮基-4-[¹²⁵I]碘苯氧基]甲基咪唑啉，[¹²⁵I]-AZIPI）标记不同物种中的咪唑啉结合蛋白，并在COS 7细胞中瞬时表达MAO-A和-B后，进一步表征了咪唑啉结合蛋白与单胺氧化酶之间的关系。大鼠和人类中MAO-A和-B的物种同源物在表观分子量上相差约2000 Da。在大鼠和人类肝脏中，[¹²⁵I]-AZIPI鉴定出的肽段表观分子量与MAO的物种同源物相似。在用编码MAO-A或-B的人cDNA克隆转染的COS-7细胞制备的膜中，分子量约为63,000（MAO-A）和约59,000（MAO-B）的肽段也被光标记。额外的实验表明，MAO-A和-B上的咪唑啉结合结构域表现出不同的配体识别特性。咪唑啉2-(4,5-二氢咪唑-2-基)-喹啉（BU224）对人肝脏MAO-B的共价标记抑制作用比对胎盘MAO-A更敏感。这些数据表明，MAO的A和B同工型具有在配体识别特性上不同的咪唑啉结合结构域。通过咪唑啉结合结构域对MAO活性的变构调节在与酶表达升高相关的各种疾病状态或酶是治疗靶点的情况下可能具有重要意义。
