THE 58 KDA MOUSE SELENOPROTEIN IS A BCNU-SENSITIVE THIOREDOXIN REDUCTASE

The flavoprotein thioredoxin reductase [EC 1.6.4.5] NADPH+H+ + thiored oxin-S-2 --> NADP(+) + thioredoxin-(SH)(2)) was isolated from mouse Eh rlich ascites tumour (EAT) cells, Like the counterpart from human plac enta but unlike the known thioredoxin reductases from non-vertebrate o rganisms, the mouse enzyme has found to contain 1 equivalent of seleni um per subunit of 58 kDa, The K-M values were 4.5 mu M for NADPH, 480 mu M for DTNB and 36 mu M for Escherichia coli thioredoxin, the turnov er number with DTNB being approximate to 40 s(-1). As mouse is a stand ard animal model in cancer and malaria research, thioredoxin reductase and glutathione reductase [EC 1.6.4.2] from EAT cells, were compared with each other, While both enzymes in their 2-electron reduced form a re targets of the cytostatic drug carmustine (BCNU), no immunologic cr oss-reactivity between the two mouse disulfide reductases was observed . (C) 1997 Federation of European Biochemical Societies.