Studies of crystalline trimethylamine dehydrogenase in three oxidation states and in the presence of substrate and inhibitor.

Crystals of trimethylamine dehydrogenase have been examined by difference Fourier methods at 6.0-A resolution after partial reduction by substrate and by dithionite in the presence of inhibitor. Similar studies of the inhibited oxidized enzyme and of the enzyme reduced fully by dithionite alone were also carried out. In all cases ligand binding at the active site occurred. In addition, there were small structural changes, possibly side chain movements, in the inhibited oxidized enzyme and somewhat larger changes in the partially reduced crystals. The largest changes occurred with the fully reduced enzyme. However, in no cases were subunit or domain movements observed nor were changes observed in the position of the FMN or [4Fe-4S] cofactors. Parallel studies of crystalline trimethylamine dehydrogenase were carried out by EPR spectroscopy. The results show that the electronic states of the crystalline enzyme under the conditions of the difference Fourier studies are comparable to those which occur in solution under similar conditions.