OBSERVATION OF 2 DIFFERENT CHROMOPHORES IN THE RESTING STATE OF MONOAMINE-OXIDASE-B BY FLUORESCENCE SPECTROSCOPY

Catalytically active monoamine oxidase (MAO) is believed to exist as a dimer with each subunit containing a covalently attached flavin cofac tor. Fluorescence spectroscopy performed on the resting state enzyme r esulted in two separate fluorescence emissions at 480 nm and 530 nm wi th excitation maxima at lambda(ex) = 412 nm and lambda(ex) = 450 nm, r espectively. Inactivation of MAO with pargyline resulted in concomitan t loss of the absorbance at 450 nm without change in the 412 nm absorp tion; there also was a decrease in the emission intensity at 530 nm, w hile the emission at 480 nm remained unchanged. The 480 nm emission de creased and the 530 nm emission intensity increased, when the enzyme w as heat denatured in the presence of NaDodSO(4). From these results, i t is clear that there are two different chromophores present in the re sting state enzyme; the 530 nm chromophore is consistent with an oxidi zed flavin, while the 480 nm chromophore could be a flavin semiquinone . (C) 1994 Academic Press, Inc.