| Abstract: | 本實驗主要目的為探討過氧化緊迫時,維生素E對蛋白質硫氫基(Sulfhydryls)及細胞膜的保護作用。肝細胞分別取自經餵飼不含維生素E或含100ppm或15,000ppm維生素E飼料為期12週的雄性大白鼠,經24小時培養後,給與0.5mM t-butyl hydroperoxide(t-BuOOH)處理。由於Carbonic anhydrase III(CA III)已知擁有兩個活性硫氫基,在氧化緊迫下可與Glutathione(GSH)形成Mixed-disulfides(又稱S-glutathionation),因此被選為蛋白質硫氫基是否受到修飾的代表分子。CA III S-glutathionation將以等電點電泳法(Isoelectric focusing,IEF)和西方墨點法(Western blotting)進行分析,並以影像分析(Image analysis)予以定量。結果顯示硫氫基的修飾可受到細胞維生素E的影響,肝細胞給與0.5mM t-BuOOH後,CA III S-glutathionation迅速發生,在高維生素E組,最大硫氫基修飾作用於3分鐘後達到,然而,維生素E正常及缺乏組,此蛋白質修飾則繼續增加並於9分鐘達到最高。經由影像定量分析,結果亦指出缺乏維生素E的細胞的確有較多CA III硫氫基與GSH反應,轉換為修飾態(S-glutathionated forms)。繼最大修飾反應後,逆反應(Deglutathionation)隨之發生,且此反應速率也與細胞內維生素E水準有正相關,維生素E愈高Deglutathionation也愈快。至於細胞內GSH在t-BuOOH處理後也快速氧化為GSSG,所有細胞不論維生素E濃度的高低,其GSH的氧化均於3分鐘後達到最大。隨之,一如維生素E與CA III deglutathionation的關係,GSSG也於3分鐘後逐一還原為GSH,而且此還原反應也與維生素E濃度相關。至於脂質過氧化程度(TBARS)則正確反應出肝細胞維生素E水準。細胞膜Blebbing程度也是維生素E缺乏細胞>正常細胞>高維生素E細胞。以上結果顯示,維生素E除了扮演自由基清除者保護細胞膜脂質免於過氧化外,同時透過抑制蛋白質發生修飾或活化其還原反應,對細胞內蛋白質硫氫基的維持也扮演有重要角色。
This study examines the effects of vitamin E with respect to maintaining the protein reactive sulfhydryl groups under oxidative stress. Hepatocytes were prepared from male Sprague-Dawley rats which had been fed diets with three vitamin E levels, 0, 100, and 15,000ppm, respectively, for 12 weeks. Cells were isolated by collagenase perfusion and treated with 0.5mM of t-butyl hydroperoxide (t-BuOOH) after 24 h in culture. Carbonic anhydrase III (CA III), owns two reactive sulfhydryls could react with GSH under oxidative stress, was chosen as the marker. CA III S-glutathionation was measured by isoelectric focusing/immunoblotting. Results indicated that thiol modification of CA III was induced and the pattern of modification was dependent on the vitamin E status. With t-BuOOH treatment, CA III S-glutathionation was quickly induced and maximum modification was achieved at 3 min of cells isolated from excess vitamin E-fed rats. However, modification was continuously increased and reached maximum at 9 min of vitamin E-normal or-deficient cells. With image analysis, greater proportion of CA III switched to S-glutathionated form of vitamin E deficient hepatocytes would suggest the intense thiol modification in these cells. Following the maximum modification, a reversion occurred, however, the rate of reversion was also related to vitamin E status. Glutathione was also dramatically switched to oxidized state at 3 min in all treatments then gradually reverse to reduced state. Similar to the reversion of CA III modification, the rate of glutathione disulfide reduction was positively correlated to vitamin E status. The production of thiobarbituric acid-reactive substances also corresponded to vitamin E status and was significantly inhibited in hepatocytes from vitamin E supplemented rats. These results would suggest that vitamin E as a radical scavenger not only inhibits lipid peroxidation but also plays a role in maintaining the protein thiols under oxidative stress by inhibiting S-glutathionated CA III formation or accelerating the reversion of modified protein. |
