EC 2.5.1.154     
Accepted name: corrinoid adenosyltransferase EutT
Reaction: 2 ATP + 2 cob(II)alamin + a reduced flavoprotein = 2 diphosphate + 2 phosphate + 2 adenosylcob(III)alamin + an oxidized flavoprotein (overall reaction)
(1a) 2 cob(II)alamin + 2 [corrinoid adenosyltransferase] = 2 [corrinoid adenosyltransferase]-cob(II)alamin
(1b) a reduced flavoprotein + 2 [corrinoid adenosyltransferase]-cob(II)alamin = an oxidized flavoprotein + 2 [corrinoid adenosyltransferase]-cob(I)alamin (spontaneous)
(1c) 2 ATP + 2 [corrinoid adenosyltransferase]-cob(I)alamin = 2 diphosphate + 2 phosphate + 2 adenosylcob(III)alamin + 2 [corrinoid adenosyltransferase]
Other name(s): eutT (gene name)
Systematic name: ATP:cob(II)alamin Coβ-adenosyltransferase (diphosphate-forming)
Comments: The corrinoid adenosylation pathway comprises three steps: (i) reduction of Co(III) within the corrinoid to Co(II) by a one-electron transfer. This can occur non-enzymically in the presence of dihydroflavin nucleotides or reduced flavoproteins [1]. (ii) Co(II) is bound by corrinoid adenosyltransferase, resulting in displacement of the lower axial ligand by an aromatic residue. The reduction potential of the 4-coordinate Co(II) intermediate is raised by ~250 mV compared with the free compound, bringing it to within physiological range. This is followed by a second single-electron transfer from either free dihydroflavins or the reduced flavin cofactor of flavoproteins, resulting in reduction to Co(I) [4]. (iii) the Co(I) conducts a nucleophilic attack on the adenosyl moiety of ATP, resulting in transfer of the deoxyadenosyl group and oxidation of the cobalt atom to Co(III) state. Three types of corrinoid adenosyltransferases, not related by sequence, have been described. In the anaerobic bacterium Salmonella enterica they are encoded by the cobA gene (a housekeeping enzyme involved in both the de novo biosynthesis and the salvage of adenosylcobalamin), the pduO gene (involved in (S)-propane-1,2-diol utilization), and the eutT gene (involved in ethanolamine utilization). The first two types, which produce triphosphate, are classified as EC 2.5.1.17, corrinoid adenosyltransferase, while the EutT type hydrolyses triphosphate to diphosphate and phosphate during catalysis and is thus classified separately.
References:
1.  Fonseca, M.V. and Escalante-Semerena, J.C. Reduction of Cob(III)alamin to Cob(II)alamin in Salmonella enterica serovar typhimurium LT2. J. Bacteriol. 182 (2000) 4304–4309. [PMID: 10894741]
2.  Sheppard, D.E., Penrod, J.T., Bobik, T., Kofoid, E. and Roth, J.R. Evidence that a B12-adenosyl transferase is encoded within the ethanolamine operon of Salmonella enterica. J. Bacteriol. 186 (2004) 7635–7644. [PMID: 15516577]
3.  Buan, N.R. and Escalante-Semerena, J.C. Purification and initial biochemical characterization of ATP:cob(I)alamin adenosyltransferase (EutT) enzyme of Salmonella enterica. J. Biol. Chem. 281 (2006) 16971–16977. [PMID: 16636051]
4.  Mera, P.E. and Escalante-Semerena, J.C. Dihydroflavin-driven adenosylation of 4-coordinate Co(II) corrinoids: are cobalamin reductases enzymes or electron transfer proteins. J. Biol. Chem. 285 (2010) 2911–2917. [PMID: 19933577]
5.  Moore, T.C., Mera, P.E. and Escalante-Semerena, J.C. the Eutt enzyme of Salmonella enterica is a unique ATP:cob(I)alamin adenosyltransferase metalloprotein that requires ferrous ions for maximal activity. J. Bacteriol. 196 (2014) 903–910. [PMID: 24336938]
[EC 2.5.1.154 created 2021]