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INTERACTION OF DIHYDROOROTATE DEHYDROGENASE WITH LIGHT *
Author(s) -
Miller Richard W.,
Kerr Carolyn T.
Publication year - 1967
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1967.tb09654.x
Subject(s) - flavin group , flavoprotein , chemistry , photochemistry , absorbance , semiquinone , cofactor , dehydrogenase , light intensity , enzyme , biochemistry , quinone , chromatography , physics , optics
— Several flavoproteins are known to undergo photoactivated reduction by EDTA. However, the effects of visible light on the non‐heme iron containing flavoproteins have not been characterized previously. Dihydroorotate dehydrogenase was studied as an example of this class of enzymes. Interaction with visible light was found to be complex. Under low intensity photoirradiation of long duration the anaerobic enzyme was partially reduced to a form having increased absorbance at 630 nm. Similar absorbance changes have been correlated with semiquinone species. However, the irradiated enzyme exhibited irreversible changes in catalytic function. Activity with NADH was greatly reduced and a portion of the flavin coenzyme content was labilized. Fluorescence intensity of the enzyme was markedly increased by exposure to light, confirming partial degradation of a catalytic site. Isothermal irradiation with light of high intensity in the range 330–600 nm caused the enzyme to be reduced rapidly. Spectroscopic changes were observed which persisted after reoxidation of flavins. Intense new absorbance maxima between 310 and 330 nm together with a large decrase in absorbance at 450 nm were noted. Under controlled conditions approximately half of the total flavin and practically all of the bound FAD were labilized. NADH oxidase activity and NADH linked reduction of orotate were selectively lost. The correlation between FAD labilization and loss of activity strengthens the hypothesis that FAD represents the site of activity with NADH. Activity with NADH was partially restored by incubation of the irradiated enzyme with FAD or FMN.