Ghiggeri G M, Candiano G, Ginevri F, Gusmano R, Ciardi M R, Perfumo F, Delfino G, Cuniberti C, Queirolo C
Kidney Int. 1987 Jul;32(1):69-77. doi: 10.1038/ki.1987.173.
It is well accepted that the molecular charge and conformation of serum proteins are major determinants of their glomerular filtration, but few studies characterizing the molecular features of circulating proteins in renal diseases are currently available. In 11 children affected by minimal change nephropathy (MCN) we determined the electrical charge and the fluorescence quantum yield of Tyrosine (Tyr) and Tryptophan (Trp) (taken as index of conformation) of serum and urinary albumin before and after steroid-induced remission of proteinuria. In all proteinuric children at the onset of the disease, urinary albumin was formed by one band with an isoelectric point (pI) of 4.7 (pI of the native protein), and by numerous other, less anionic bands with pIs between 4.8 and 5.5 accounting for about 50% of the total amount of this protein. The normalization of proteinuria which followed steroid therapy was characterized by the disappearance in urines of the less anionic fraction and by the appearance of numerous isoforms with a pI still more anionic (pI less than 4.7) than normal. At the same time, in the proteinuric phase, the fluorescence quantum yield of Trp of urinary albumin was markedly quenched, returning to near normal levels after steroid-induced remission of proteinuria. These data indicate that in MCN the charge-dependent renal selectivity properties are partially maintained and that the less anionic isoforms of albumin are a main component of urinary albumin. Together with the electrical charge, the conformation of albumin as a major determinant of its urinary excretion in MCN must also be considered.
血清蛋白的分子电荷和构象是其肾小球滤过的主要决定因素，这一点已得到广泛认可，但目前关于肾脏疾病中循环蛋白分子特征的研究很少。我们对11名患微小病变肾病（MCN）的儿童，测定了蛋白尿经类固醇诱导缓解前后血清和尿白蛋白中酪氨酸（Tyr）和色氨酸（Trp）的电荷以及荧光量子产率（作为构象指标）。在所有蛋白尿期患儿疾病初发时，尿白蛋白由一条等电点（pI）为4.7（天然蛋白的pI）的条带以及许多其他pI在4.8至5.5之间、阴离子性较弱的条带组成，这些条带约占该蛋白总量的50%。类固醇治疗后蛋白尿的正常化表现为尿中阴离子性较弱的部分消失，以及出现许多pI比正常情况更具阴离子性（pI小于4.7）的异构体。同时，在蛋白尿期，尿白蛋白中Trp的荧光量子产率明显猝灭，在类固醇诱导蛋白尿缓解后恢复到接近正常水平。这些数据表明，在MCN中，电荷依赖性肾脏选择性特性部分得以维持，且白蛋白的阴离子性较弱的异构体是尿白蛋白的主要成分。除了电荷外，白蛋白的构象作为其在MCN中尿排泄的主要决定因素也必须加以考虑。
