Perna A F, Castaldo P, De Santo N G, di Carlo E, Cimmino A, Galletti P, Zappia V, Ingrosso D
Division of Nephrology, Department of Pediatrics, Second University of Naples, School of Medicine and Surgery, Naples, Italy.
Kidney Int. 2001 Jun;59(6):2299-308. doi: 10.1046/j.1523-1755.2001.00747.x.
Several alterations of protein structure and function have been reported in uremia. Impairment of a transmethylation-dependent protein repair mechanism possibly related to a derangement in homocysteine metabolism is also present in this condition, causing erythrocyte membrane protein damage. Homocysteine may affect proteins via the accumulation of its parent compound S-adenosylhomocysteine (AdoHcy), a powerful in vivo methyltransferase inhibitor. However, since plasma homocysteine is mostly protein bound, a direct influence on protein structures cannot be ruled out. We measured the levels of L-isoaspartyl residues in plasma proteins of uremic patients on hemodialysis. These damaged residues are markers of molecular age, which accumulate when transmethylation-dependent protein repair is inhibited and/or protein instability is increased.
L-isoaspartyl residues in plasma proteins were quantitated using human recombinant protein carboxyl methyl transferase (PCMT). Plasma concentrations of homocysteine metabolites were also measured under different experimental conditions in hemodialysis patients.
The concentration of damaged plasma proteins was increased almost twofold compared to control (controls 147.83 +/- 17.75, uremics 282.80 +/- 26.40 pmol of incorporated methyl groups/mg protein, P < 0.003). The major protein involved comigrated with serum albumin. Although hyperhomocysteinemia caused a redistribution of thiols bound to plasma proteins, this mechanism did not significantly contribute to the increase in isoaspartyl residues. The S-adenosylmethionine (AdoMet)/AdoHcy concentration ratio, an indicator of the flux of methyl group transfer, was altered. This ratio was partially corrected by folate treatment (0.385 +/- 0.046 vs. 0.682 +/- 0.115, P < 0.01), but protein L-isoaspartate content was not.
Plasma protein damage, as determined by protein L-isoaspartyl content, is increased in uremia. This alteration is to be ascribed to an increased protein structural instability, rather than the effect of hyperhomocysteinemia.
已有报道称尿毒症患者存在多种蛋白质结构和功能的改变。在这种情况下，还存在一种可能与同型半胱氨酸代谢紊乱相关的依赖转甲基化的蛋白质修复机制受损，导致红细胞膜蛋白损伤。同型半胱氨酸可能通过其母体化合物S - 腺苷同型半胱氨酸（AdoHcy）的积累来影响蛋白质，AdoHcy是一种强大的体内甲基转移酶抑制剂。然而，由于血浆中的同型半胱氨酸大多与蛋白质结合，因此不能排除其对蛋白质结构的直接影响。我们检测了接受血液透析的尿毒症患者血浆蛋白中L - 异天冬氨酸残基的水平。这些受损残基是分子老化的标志物，当依赖转甲基化的蛋白质修复受到抑制和/或蛋白质不稳定性增加时会积累。
使用人重组蛋白羧基甲基转移酶（PCMT）对血浆蛋白中的L - 异天冬氨酸残基进行定量。还在不同实验条件下检测了血液透析患者血浆中同型半胱氨酸代谢产物的浓度。
与对照组相比，受损血浆蛋白的浓度几乎增加了两倍（对照组：147.83±17.75，尿毒症患者：282.80±26.40 pmol甲基基团掺入量/mg蛋白，P < 0.003）。涉及的主要蛋白质与血清白蛋白共迁移。虽然高同型半胱氨酸血症导致了与血浆蛋白结合的硫醇重新分布，但这种机制对异天冬氨酸残基增加的贡献并不显著。甲基基团转移通量的指标S - 腺苷甲硫氨酸（AdoMet）/AdoHcy浓度比发生了改变。叶酸治疗部分纠正了该比值（0.385±0.046对0.682±0.115，P < 0.01），但蛋白质L - 异天冬氨酸含量未得到纠正。
根据蛋白质L - 异天冬氨酸含量测定，尿毒症患者血浆蛋白损伤增加。这种改变应归因于蛋白质结构不稳定性增加，而非高同型半胱氨酸血症的影响。
