Reaction: 2'-deoxyribonucleoside 5'-triphosphate + thioredoxin disulfide + H2O = ribonucleoside 5'-triphosphate + thioredoxin
Other name(s): ribonucleotide reductase (ambiguous); 2'-deoxyribonucleoside-triphosphate:oxidized-thioredoxin 2'-oxidoreductase
Systematic name: 2'-deoxyribonucleoside-5'-triphosphate:thioredoxin-disulfide 2'-oxidoreductase
Comments: The enzyme, characterized from the bacterium Lactobacillus leichmannii, is similar to class II ribonucleoside-diphosphate reductase (cf. EC 1.17.4.1). However, it is specific for the triphosphate versions of its substrates. The enzyme contains an adenosylcobalamin cofactor that is involved in generation of a transient thiyl (sulfanyl) radical on a cysteine residue. This radical attacks the substrate, forming a ribonucleotide 3'-radical, followed by water loss to form a ketyl (α-oxoalkyl) radical. The ketyl radical is reduced to 3'-keto-deoxynucleotide concomitant with formation of a disulfide anion radical between two cysteine residues. A proton-coupled electron-transfer from the disulfide radical to the substrate generates a 3'-deoxynucleotide radical, and the final product is formed when the hydrogen atom that was initially removed from the 3'-position of the nucleotide by the thiyl radical is returned to the same position. The disulfide bridge is reduced by the action of thioredoxin. cf. EC 1.1.98.6, ribonucleoside-triphosphate reductase (formate).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9068-66-0
References:
1. Blakley, R.L. Cobamides and ribonucleotide reduction. I. Cobamide stimulation of ribonucleotide reduction in extracts of Lactobacillus leichmannii. J. Biol. Chem. 240 (1965) 2173-2180. [PMID: 14299643]
2. Goulian, M. and Beck, W.S. Purification and properties of cobamide-dependent ribonucleotide reductase from Lactobacillus leichmannii. J. Biol. Chem. 241 (1966) 4233-4242. [PMID: 5924645]
3. Stubbe, J., Ackles, D., Segal, R. and Blakley, R.L. On the mechanism of ribonucleoside triphosphate reductase from Lactobacillus leichmannii. Evidence for 3' C--H bond cleavage. J. Biol. Chem. 256 (1981) 4843-4846. [PMID: 7014560]
4. Ashley, G.W., Harris, G. and Stubbe, J. The mechanism of Lactobacillus leichmannii ribonucleotide reductase. Evidence for 3' carbon-hydrogen bond cleavage and a unique role for coenzyme B12. J. Biol. Chem. 261 (1986) 3958-3964. [PMID: 3512563]
5. Lawrence, C.C. and Stubbe, J. The function of adenosylcobalamin in the mechanism of ribonucleoside triphosphate reductase from Lactobacillus leichmannii. Curr. Opin. Chem. Biol. 2 (1998) 650-655. [PMID: 9818192]
6. Licht, S.S., Booker, S. and Stubbe, J. Studies on the catalysis of carbon-cobalt bond homolysis by ribonucleoside triphosphate reductase: evidence for concerted carbon-cobalt bond homolysis and thiyl radical formation. Biochemistry 38 (1999) 1221-1233. [PMID: 9930982]