The flavin environment in old yellow enzyme. An evaluation of insights from spectroscopic and artificial flavin studies.

Spectroscopic and chemical modification studies of modified flavins bound to old yellow enzyme have led to predictions about the flavin environment of this enzyme. These studies analyzed solvent accessibility and hydrogen bonding patterns of particular flavin atoms, in addition to suggesting amino acid residues that are in close proximity to those atoms. Here, these studies are evaluated in the light of the crystal structure of old yellow enzyme to reveal that the spectroscopic and modified flavin results are generally consistent with the crystal structure. This highlights the fact that these are useful methods for studying flavin binding site structure. Although several of the inferred properties of the flavin environment are not consistent with the crystal structure, these discrepancies occurred in cases where an incorrect choice was made from among multiple plausible explanations for an experimental result. We conclude that modified flavin studies are powerful probes of flavin environment; however, it is risky to specify details of interactions, especially because of uncertainties due to induced charge delocalization in the flavin.