Lewicki J A, Printz J M, Printz M P
Am J Physiol. 1983 Apr;244(4):H577-85. doi: 10.1152/ajpheart.1983.244.4.H577.
Rabbit plasma angiotensinogen was purified 1,390-fold by classical purification procedures. Analytical polyacrylamide gel electrophoresis and direct activity assay revealed that the purified preparations were greater than 90% native angiotensinogen. The purified angiotensinogen was radiolabeled with 125I-Na using the immobilized lactoperoxidase-Sepharose method and injected into awake, conscious rabbits. Complex clearance kinetics were observed that were resolved by a three-component model; half of the protein was cleared rapidly (t1/2 = 6 and 54 min), presumably reflecting mixing and redistribution, whereas half exhibited slow clearance kinetics (t1/2 = 8.58 h). The clearance kinetics were independent of the method of iodination and the isoelectric-point microheterogeneity of the protein. With knowledge of clearance kinetics we tested whether cerebrospinal fluid angiotensinogen could derive from the plasma pool. After injection of approximately 100 microCi 125I-angiotensinogen into the rabbit circulation, little 125I-angiotensinogen was detected in cerebrospinal fluid. Further, the brain space of 125I-angiotensinogen was identical to that of 125I-albumin, a protein that does not partition from plasma into the central nervous system. We conclude that the brain prohormone does not appear to be derived from the plasma pool.
通过经典纯化程序，兔血浆血管紧张素原被纯化了1390倍。分析型聚丙烯酰胺凝胶电泳和直接活性测定表明，纯化后的制剂中天然血管紧张素原含量超过90%。采用固定化乳过氧化物酶-琼脂糖法，用125I-Na对纯化后的血管紧张素原进行放射性标记，并注入清醒、有意识的兔子体内。观察到复杂的清除动力学，可用三组分模型解析；一半蛋白质清除迅速（t1/2 = 6分钟和54分钟），这可能反映了混合和再分布情况，而另一半则表现出缓慢的清除动力学（t1/2 = 8.58小时）。清除动力学与碘化方法和蛋白质的等电点微不均一性无关。基于对清除动力学的了解，我们测试了脑脊液血管紧张素原是否可能来源于血浆池。向兔循环系统中注入约100微居里的125I-血管紧张素原后，在脑脊液中检测到的125I-血管紧张素原很少。此外，125I-血管紧张素原在脑内的分布空间与125I-白蛋白相同，白蛋白是一种不会从血浆进入中枢神经系统的蛋白质。我们得出结论，脑前体激素似乎并非来源于血浆池。
