Morgan W T
Ann Clin Res. 1976;8 Suppl 17:223-32.
Hemopexin binds proto-, meso-, or deutero-ferriheme with high affinity, forming an equimolar, low-spin complex. The ferroheme-hemopexin complex, which coordinates with CO and readily autoxidizes, is also low-spin. Formation of the ferriheme-hemopexin complex requires essential histidine and tryptophan residues and induces changes in the protein's tertiary structure. These changes may be important for the uptake of the heme-hemopexin complex by hepatocytes. Hemopexin also binds other porphyrins including protoporphyrin IX, and uro- and coproporphyrins I and III in a 1:1 molar ratio, but they are readily displaced by heme and do not produce discernable changes in the protein's conformation. In preliminary experiments, a selective interaction in vitro between heme-hemopexin and isolated rat hepatocytes has been demonstrated. This information is used as the basis for proposed models of the heme-binding site of hemopexin and of the interaction of heme-hemopexin with the parenchymal cells of the liver.
血红素结合蛋白以高亲和力结合原血红素、中血红素或次血红素，形成等摩尔的低自旋复合物。亚铁血红素 - 血红素结合蛋白复合物与一氧化碳配位并易于自氧化，也是低自旋的。高铁血红素 - 血红素结合蛋白复合物的形成需要必需的组氨酸和色氨酸残基，并会引起蛋白质三级结构的变化。这些变化可能对肝细胞摄取血红素 - 血红素结合蛋白复合物很重要。血红素结合蛋白还以1:1的摩尔比结合其他卟啉，包括原卟啉IX、尿卟啉I和III以及粪卟啉I和III，但它们很容易被血红素取代，并且不会在蛋白质构象中产生可察觉的变化。在初步实验中，已证明血红素 - 血红素结合蛋白与分离的大鼠肝细胞之间在体外存在选择性相互作用。这些信息被用作提出的血红素结合蛋白血红素结合位点模型以及血红素 - 血红素结合蛋白与肝脏实质细胞相互作用模型的基础。
