Photoinduced electron transfer in glucose oxidase: a picosecond time-resolved ultraviolet resonance Raman study

Picosecond time-resolved ultraviolet resonance Raman (UVRR) spectroscopy has been applied to photoinduced electron transfer (ET) of glucose oxidase (GOD). In this study, we succeeded in directly observing changes in the aromatic amino acid residues in the photoinduced ET of GOD for the first time. UVRR spectra excited at 226 nm showed bands from Trp and Tyr residues. An intensity decrease of the Trp UVRR bands and the appearance of the UVRR bands attributable to Trp(center dot+) were observed in the time-resolved spectra. In the time-resolved UVRR spectra excited at 240 nm, the intensity decrease of the flavin adenine dinucleotide (FAD) bands was also observed on the same time scale. These results showed that the Trp residue(s) serves as an electron donor to excited-state FAD in the photoinduced ET of GOD. The comparison of the temporal changes of the Trp and FAD band intensities suggested that the ET from the Trp residue(s) to the FAD occurs with a time constant of similar to 1.5 ps. Copyright (C) 2008 John Wiley & Sons, Ltd.