QUINOLINE 2-OXIDOREDUCTASE AND 2-OXO-1,2-DIHYDROQUINOLINE 5,6-DIOXYGENASE FROM COMAMONAS-TESTOSTERONI-63 - THE FIRST 2 ENZYMES IN QUINOLINEAND 3-METHYLQUINOLINE DEGRADATION
S. Schach et al., QUINOLINE 2-OXIDOREDUCTASE AND 2-OXO-1,2-DIHYDROQUINOLINE 5,6-DIOXYGENASE FROM COMAMONAS-TESTOSTERONI-63 - THE FIRST 2 ENZYMES IN QUINOLINEAND 3-METHYLQUINOLINE DEGRADATION, European journal of biochemistry, 232(2), 1995, pp. 536-544
The enzymes catalysing the first two steps of quinoline and 3-methylqu
inoline degradation by Comamonas testosteroni 63 were investigated. Qu
inoline 2-oxidoreductase, which catalyses the hydroxylation of (3-meth
yl-)quinoline to (3-methyl-)2-oxo-1,2-dihydroquinoline, was purified t
o apparent homogeneity. The native enzyme, with a molecular mass of 36
0 kDa, is composed of three non-identical subunits (87, 32, and 22 kDa
), occurring in a ratio of 1.16:1:0.83. Containing FAD, molybdenum, ir
on, and acid-labile sulfur in the stoichiometric ratio of 2:2:8:8, the
enzyme belongs to the molybdo-iron/sulfur flavoproteins. Molybdopteri
n cytosine dinucleotide is the organic part of the pterin molybdenum c
ofactor. Comparison of N-terminal amino acid sequences revealed simila
rities to a number of procaryotic molybdenum-containing hydroxylases.
Especially the N-termini of the beta-subunits of the quinoline 2-oxido
reductases from Comamonas testosteroni 63, Pseudomonas putida 86, and
Rhodococcus spec. B1, and of quinoline-4-carboxylic acid 2-oxidoreduct
ase from Agrobacterium spec. 1B showed striking similarities. Further
degradation of (3-methyl-)2-oxo-1,2-dihydroquinoline proceeds via diox
ygenation st the benzene ring, i.e. at 5,6-position [Schach, S., Schwa
rz, G., Fetzner, S. & Lingens, F. (1993) Biol. Chem. Hoppe-Seyler 374,
175-181]. 2-Oxo-1,2-dihydroquinoline 5,6-dioxygenase was partially pu
rified; NADH and oxygen are required for the reaction, and the enzymic
activity is enhanced 1.5-fold by addition of Fe2+ ions. Unexpectedly,
this aromatic ring dioxygenase did not separate into distinct protein
components, but is apparently a single-component enzyme. The molecula
r mass was estimated to be about 260 kDa. 2-Oxo-1,2-dihydroquinoline 5
,6-dioxygenase is very thermolabile. However, dithioerythritol and low
concentrations of substrate had a moderately stabilizing effect. 2-Ox
o-1,2-dihydroquinoline 5,6-dioxygenase is inhibited by sulfhydryl-bloc
king agents, by metal-chelating agents, and by the flavin analogues qu
inacrine and acriflavin.