M. Enescu et al., EXCITED-STATE DYNAMICS OF FULLY REDUCED FLAVINS AND FLAVOENZYMES STUDIED AT SUBPICOSECOND TIME RESOLUTION, Photochemistry and photobiology, 68(2), 1998, pp. 150-156
The photophysics of the fully reduced states of a number of flavins (f
lavin mononucleotide, flavin adenine dinucleotide and 3-N-methyllumifl
avin) and flavoenzymes (glucose oxidase from Aspergillus niger and the
flavodehydrogenase component isolated from flavocytochrome b(2)) was
studied using subpicosecond laser excitation at lambda = 312 mm. The p
rompt transient absorption spectra (measured from 400 to 850 nm) were
all closely similar in the ease of the free flavins in aqueous solutio
n. The decay of the transient absorbance obeyed biexponential kinetics
with a fast component of lifetime ranging from 4 to 130 ps and a slow
er phase with a lifetime above 1 ns. The spectral structure changed ap
preciably during the rapid decay phase. In contrast, in the case of th
e enzymes only a very slight decay was apparent over the probed time i
nterval (1 us) and the shape of the spectrum remained unchanged. It is
proposed that the two transient spectra appearing in the free flavins
correspond to two conformations differing by their degree of nonplana
rity, whereas in the flavoenzymes only one conformation is possible.