PHYSIOLOGICAL ROLES OF SELENIUM WITH SPECIAL REFERENCE TO GUINEA PIGS

为了阐明硒作为一种抗氧化剂的生理作用，研究了硒蛋白在豚鼠体内的表达和功能。豚鼠有两个明显的特征，即，谷胱甘肽过氧化物酶（GPx）是其他哺乳动物体内主要的硒蛋白，其活性极低，不能合成维生素C。我们发现，除GPx外，其他硒蛋白如磷脂氢过氧化物谷胱甘肽过氧化物酶和硫氧还蛋白还原酶（TrxR）在豚鼠体内大量表达。这表明在豚鼠中并非所有硒蛋白的表达都受到抑制。TrxR的最高活性被发现在肾上腺中，其具有最高浓度的维生素C。我们证实了TrxR在硫氧还蛋白的存在下减少脱氢抗坏血酸（DHA）的能力。在豚鼠组织中的TrxR的活性几乎没有下降时，受到缺硒饮食。同样，DHA还原几乎不受硒缺乏豚鼠。这些结果与大鼠中TrxR和DHA减少的活性的显著降低形成对比。因此，豚鼠中含硒的TrxR可能在维持还原型维生素C方面发挥重要作用。

To elucidate physiological roles of selenium (Se) as an antioxidant, the expression and functions of selenoproteins in guinea pigs were examined. The guinea pigs have two distinct characteristics ; i.e., extremely low activity of glutathione peroxidase (GPx), which is the major selenoprotein in other mammals, and an inability of synthesizing vitamin C.We found that othter selenoproteins than GPx such as phospholipid hydroperoxide glutathione peroxidase and thioredoxin reductase (TrxR) are expressed substantially in guinea pigs. This suggests that the expression of not all selenoproteins is suppressed in guinea pigs. The highest activity of TrxR was found in adrenal glands, which had the highest concentration of vitamtin C.We confirmed the ability of TrxR for reducing dehydroascorbic acid (DHA) in the presence of thioredoxin. The activity of TrxR in guinea pig tissues hardly decreased when subjected to a Se-deficient diet. Similarly, DHA-reducing was hardly affected by Se deficiency in guinea pigs. These results were in contrast with a marked reduction of both activities of TrxR and DHA-reduction in rats. Thus, Se-containing TrxR in guinea pigs may play an important role in maintaining a reduced form of vitamin C.