Huq A H, Ito M, Naito E, Saijo T, Takeda E, Kuroda Y
Department of Pediatrics, School of Medicine, University of Tokushima, Japan.
Pediatr Res. 1991 Jul;30(1):11-4. doi: 10.1203/00006450-199107000-00003.
The deficiency of pyruvate dehydrogenase enzyme complex causes congenital lactic acidemia and devastating neurologic abnormalities in newborns and children. In the majority of cases, the basic defect appears to be in the pyruvate dehydrogenase (E1) component, which consists of two subunits, alpha and beta. Whereas some patients are deficient of a single subunit, in other patients both subunits of E1 are missing. To find out why two proteins were deficient, we investigated the cultured fibroblasts of a female patient who had missing E1-alpha and E1-beta protein bands on Western blot. Radiolabeling-immunoprecipitation studies with 35S-methionine revealed that patient fibroblasts synthesized normal sized precursor E1-alpha and E1-beta proteins, which were presumably transported into mitochondria and processed into normal sized mature proteins. However, pulse-chase analysis showed that alpha- and beta-proteins were degraded rapidly compared to normal. Our findings proved that alpha- and beta-subunits were synthesized and processed normally but failed to form a stable structure for incorporation into the pyruvate dehydrogenase complex.
丙酮酸脱氢酶复合体缺乏会导致新生儿和儿童先天性乳酸性酸中毒以及严重的神经异常。在大多数情况下，基本缺陷似乎在于丙酮酸脱氢酶（E1）组分，它由α和β两个亚基组成。有些患者缺乏单个亚基，而在其他患者中，E1的两个亚基均缺失。为了弄清楚为何两种蛋白质会缺乏，我们研究了一名女性患者的培养成纤维细胞，该患者在蛋白质免疫印迹上缺失E1-α和E1-β蛋白条带。用35S-甲硫氨酸进行的放射性标记-免疫沉淀研究表明，患者的成纤维细胞合成了正常大小的前体E1-α和E1-β蛋白，这些蛋白大概被转运到线粒体中并加工成正常大小的成熟蛋白。然而，脉冲追踪分析表明，与正常情况相比，α和β蛋白降解迅速。我们的研究结果证明，α和β亚基合成和加工正常，但未能形成稳定结构以纳入丙酮酸脱氢酶复合体。
