GLUTATHIONE-DEPENDENT HYDROGEN DONOR SYSTEM FOR CALF THYMUS RIBONUCLEOSIDE-DIPHOSPHATE REDUCTASE

Purified calf thymus ribonucleoside-diphosphate reductase (2'-deoxyribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1), showed an absolute requirement for a dithiol as hydrogen donor, whereas the natural monothiol glutathione (GSH) was inactive per se. However, a protein partially purified from thymus coupled the oxidation of GSH to the formation of deoxyribonucleotides by ribonucleotide reductase. In analogy with the ribonucleotide reductase system of Escherichia coli this protein was called glutaredoxin [Holmgren, A. (1976) Proc. Natl. Acad. Sci. USA 73, 2275-2279]. Thymus glutaredoxin had the following properties: (i) its molecular weight determined by gel chromatography was about 12,000; (ii) it was active iwth ribonucleotide reductase in the presence of GSH, NADPH, and glutathione reductase but had no activity with NADPH and thioredoxin reductase; and (iii) it was immunologically different from thioredoxin because it did not bind to antithioredoxin immunoadsorbents. Experiments on the crossreactivity of thymus and E. coli ribonucleotide reductases and the corresponding thioredoxin and glutaredoxin systems showed essentially no specificity for the homologous thioredoxin but a high species specificity for the homologous glutaredoxin.