Lyases;
Carbon-carbon lyases;
Other carbon-carbon lyases
Sysname
(6-4) photoproduct pyrimidine-lyase
Reaction(IUBMB)
(6-4) photoproduct (in DNA) = 2 pyrimidine residues (in DNA)
Substrate
(6-4) photoproduct (in DNA)
Product
pyrimidine residues (in DNA)
Comment
A flavoprotein (FAD). The overall repair reaction consists of two distinct steps, one of which is light-independent and the other one light-dependent. In the initial light-independent step, a 6-iminium ion is thought to be generated via proton transfer induced by two histidines highly conserved among the (6-4) photolyases. This intermediate spontaneously rearranges to form an oxetane intermediate by intramolecular nucleophilic attack. In the subsequent light-driven reaction, one electron is believed to be transferred from the fully reduced FAD cofactor (FADH-) to the oxetane intermediate thus forming a neutral FADH radical and an anionic oxetane radical, which spontaneously fractures. The excess electron is then back-transferred to the flavin radical restoring the fully reduced flavin cofactor and a pair of pyrimidine bases [2].
