Figure 6
Electron density showing the dual conformations of the cofactor. The local fold of the protein is indicated as a cyan tube and the side chains adjacent to the cofactor are shown in the same colour as the enzyme, while the cofactor itself is coloured green. The map obtained for the 40-day-old protein is shown in (a), with that for the 50-day-old protein shown in (b); both maps are contoured at 0.7 r.m.s.. The C2 ring clearly adopts two positions depending on its oxidation state, which are shown as C2(ox) and C2(red). In the oxidized conformation, the C2 ring possesses a carbonyl O atom substituted at the α-position; accordingly, the proportion of cofactor adopting this conformer increases with time. |