EC Number   |
Reaction |
Reference |
|---|
   1.14.99.50 | hercynine + gamma-L-glutamyl-L-cysteine + O2 = gamma-L-glutamyl-S-(hercyn-2-yl)-L-cysteine S-oxide + H2O |
- |
- |
| 1.14.99.50 | hercynine + gamma-L-glutamyl-L-cysteine + O2 = gamma-L-glutamyl-S-(hercyn-2-yl)-L-cysteine S-oxide + H2O |
catalytic mechanism in which C-S bond formation is initiated by an iron(III)-complexed thiyl radical attacking the imidazole ring of N-alpha-trimethyl histidine, proposed mechanism for EgtB-catalyzed C-S bond formation and sulfoxidation, overview |
733092 |
| 1.14.99.50 | hercynine + gamma-L-glutamyl-L-cysteine + O2 = gamma-L-glutamyl-S-(hercyn-2-yl)-L-cysteine S-oxide + H2O |
EgtB contains a conserved tyrosine residue that reacts via proton-coupled electron transfer with the iron(III)-superoxo species and creates an iron(III)-hydroperoxo intermediate, thereby preventing the possible thiolate dioxygenation side reaction. The nucleophilic C-S bond-formation step happens subsequently concomitant to relay of the proton of the iron(II)-hydroperoxo back to Tyr377. This is the rate-determining step in the reaction cycle and is followed by hydrogen-atom transfer from the CE1-H group of trimethyl histidine substrate to iron(II)-superoxo. In the final step, a quick and almost barrierless sulfoxidation leads to the sulfoxide product complexes. Quantum mechanics/molecular mechanics study of the mechanism of sulfoxide synthase enzymes as compared to cysteine dioxygenase enzymes and present pathways for both reaction channels in EgtB, reaction mechanism, overview. The active site contains the unusual Tyr157-Cys93 cross-link with a covalent bond between the two amino acid residues. It is believed this cross-link has a steric effect on the overall reaction mechanism. The fast CDO-type side reaction is prevented through a proton-coupled electron transfer from Tyr377 to iron(III)-superoxo, which enables the slower C-S bond formation to take place and blocks the sulfur dioxygenation side reaction |
-, 742755 |
| 1.14.99.50 | hercynine + gamma-L-glutamyl-L-cysteine + O2 = gamma-L-glutamyl-S-(hercyn-2-yl)-L-cysteine S-oxide + H2O |
two different mechanisms are analyzed, depending on whether the sulfoxidation or the S-C bond formation takes place first. The calculations suggest that the S-O bond formation occurs first between the thiolate and the ferric superoxide, followed by homolytic O-O bond cleavage. Subsequently, proton transfer from a second-shell residue Tyr377 to the newly generated iron-oxo moiety takes place, which is followed by proton transfer from the N-alpha-trimethyl histidine imidazole to Tyr377, facilitated by two crystallographically observed water molecules. Next, the S-C bond is formed between gamma-glutamyl cysteine and N-alpha-trimethyl histidine, followed by proton transfer from the imidazole CH moiety to Tyr377, which is calculated to be the rate-limiting step for the whole reaction, with a barrier of 17.9 kcal/mol in the quintet state. Optimized structures for the second, third, and fourth steps. Detailed overview |
-, 745070 |
