Resonance Raman study on the purple intermediates of the flavoenzyme D-amino acid oxidase

Abstract

Resonance Raman (RR) spectra excited at 632.8 nm within a charge transfer absorption band were obtained for a catalytic intermediate, the purple complex of D-amino acid oxidase with D-proline or D-alanine as a substrate. The resonance enhanced Raman lines around 1605 and 1360 cm −1 in either of the complexes were suggested to be derived from vibrational modes of reduced flavin molecule. Since the highest energy band at 1692 cm −1 in the RR spectrum with D-alanine was shifted to 1675 cm −1 upon [ 15N] substitution of alanine and ammonium, this Raman line in the spectrum with D-alanine or the line at 1658 cm −1 with D-proline is assigned to the CN stretching mode of an imino acid corresponding to each amino acid. These results confirm the concept that the purple intermediate of D-amino acid oxidase consists of reduced flavin and an imino acid.