Glutathione-dependent ascorbate recycling activity of rat serum albumin

An efficient regeneration of vitamin C (ascorbate) from its oxidized byprod uct, dehydroascorbate (DHAA), is necessary to maintain sufficient tissue le vels of the reduced form of the vitamin. Additionally, the recycling may be more significant in mammals, such as guinea pigs and humans, who have lost the ability to synthesize ascorbate de novo, than it is in most other mamm als who have retained the ability to synthesize the vitamin from glucose. B oth a chemical and an enzymatic reduction of DHAA to ascorbate have been pr oposed. Several reports have appeared in which proteins, including thioltra nsferase, protein disulfide isomerase, and 3-alpha-hydroxysteroid dehydroge nase, characterized for other activities have been identified as having DHA A reductase activity in vitro. Whether these previously characterized prote ins catalyze the reduction of DHAA in vivo is unclear. In the present study , a 66 kD protein was purified strictly on the basis of its DHAA-reductase activity and was identified as rat serum albumin. The protein was further c haracterized and results support the suggestion that serum albumin acts as an antioxidant and exerts a significant glutathione-dependent DHAA-reductas e activity that may be important in the physiologic recycling of ascorbic a cid. (C) 1999 Elsevier Science Inc.