J. Biol. Chem., Vol. 255, Issue 4, 1393-1398, Feb, 1980
Photodehalogenation of 7- and 8-halogen-substituted flavins. Photochemistry of the reduced flavin chromophore
V Massey, M Husain and P Hemmerich
Flavodoxin was reconstituted with 8-chloro- and 7-bromo-FMN and p-
hydroxybenzoate hydroxylase with the analogous FAD derivatives. In all
cases, the spectral properties of the artificial enzymes changed as a
result of photoreduction in the presence of ethylenediaminetetraacetate or
oxalate as sources of reducing equivalents. The same changes were found to
occur on irradiation of the enzymes which had been reduced previously in
the dark under anaerobic conditions with dithionite. Using analogous 7- and
8-chlorolumiflavins, the observed changes were shown to be due to a novel
photoreaction of the reduced flavin chromophore, in which either the 7- or
8-halogen substituent is eliminated and replaced by a proton derived from
the solvent. The same reaction was shown to occur with
7,8-bis-norlumiflavin where 1 deuterium atom was incorporated into the
molecule as a result of photoirradiation of the reduced flavin in
deuterated medium. In the case of p-hydroxybenzoate hydroxylase, both the
8-chloro-FAD and 7- bromo-FAD enzymes, as well as their 8-nor-FAD and
7-nor-FAD photoproducts, possessed catalytic activity comparable to that of
the native enzyme.
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