Comparative studies on picosecond-resolved fluorescence of d-amino acid oxidases from human with one from porcine kidney. Photoinduced electron transfer from aromatic amino acids to the excited flavin

Abstract

Fluorescence dynamics of human d-amino acid oxidase (hDAAO) and its five inhibitors have been studied in the picoseconds time domain, and compared with one in d-amino acid oxidase from porcine kidney (pkDAAO) reported. The fluorescence lifetimes were identified as 47 ps in the dimer, 235 ps in the monomer, which are compared with those of pkDAAO (45 ps-185 ps). The fluorescence lifetimes of the hDAAO did not change upon the inhibitor bindings despite of modifications in the absorption spectra. This indicates that the lifetimes of the complexes are too short to detect with the picosecond lifetime instrument. Numbers of the aromatic amino acids are similar between the both DAAOs. The fluorescence lifetimes of hDAAO were analysed with an ET theory using the crystal structure. The difference in the lifetimes of the dimer and monomer was well described in terms of difference in the electron affinity of the excited isoalloxazine (Iso*) between the two forms of the protein, though it is not known whether the structure of the monomer is different from the dimer. Three fastest ET donors were Tyr314, Trp52 and Tyr224 in the dimer, while Tyr314, Tyr224 and Tyr55 in the monomer, which are compared to those in pkDAAO, Tyr314, Tyr224 and Tyr228 in the dimer, and Tyr224, Tyr314 and Tyr228 in the monomer. The ET rate from Trp55 in hDAAO dimer was much faster compared to the rate in pkDAAO dimer. A rise component with negative pre-exponential factor was not observed in hDAAO, which are found in pkDAAO.