Smith A, Morgan W T
J Biol Chem. 1984 Oct 10;259(19):12049-53.
Plasma membranes isolated from rabbit liver retain the ability to interact specifically with heme-hemopexin. In this system, apohemopexin does not compete effectively with heme-hemopexin for binding. The membranes bind heme-hemopexin complexes with high affinity (KD = 6.8 X 10(-7) M) and with an apparent capacity of 2.3 pmol/mg of membrane protein. These membranes also retain the ability to remove heme from heme-hemopexin. The release of heme reaches a plateau after 15-30 min at 30 degrees C and does not involve metabolic energy, proteolysis of hemopexin or pH gradients. The apohemopexin formed is rapidly released from the membranes. The accumulation of heme is saturable and is affected by pH and temperature with maximum uptake occurring between pH 5.5 and 6.5 and at 30 degrees C. Interestingly, much more heme (approximately 25 pmol/mg of membrane protein) is accumulated than hemopexin at saturation, implying that the receptor can turn over several times and that a heme-binding component exists in the rabbit liver plasma membrane.
从兔肝中分离出的质膜保留了与血红素 - 血红素结合蛋白特异性相互作用的能力。在这个系统中，脱辅基血红素结合蛋白不能有效地与血红素 - 血红素结合蛋白竞争结合。质膜以高亲和力（KD = 6.8×10⁻⁷ M）结合血红素 - 血红素结合蛋白复合物，表观结合容量为2.3 pmol/mg膜蛋白。这些质膜还保留了从血红素 - 血红素结合蛋白中去除血红素的能力。在30℃下，15 - 30分钟后血红素的释放达到平台期，且不涉及代谢能量、血红素结合蛋白的蛋白水解或pH梯度。形成的脱辅基血红素结合蛋白迅速从质膜释放。血红素的积累是可饱和的，并且受pH和温度影响，在pH 5.5至6.5之间以及30℃时摄取量最大。有趣的是，饱和时积累的血红素（约25 pmol/mg膜蛋白）比血红素结合蛋白多得多，这意味着受体可以周转几次，并且兔肝质膜中存在血红素结合成分。
