Microbial metabolism of quinoline and related compounds. XV. Quinoline-4-carboxylic acid oxidoreductase from Agrobacterium spec.1B: a molybdenum-containing enzyme.

The quinoline-4-carboxylic acid oxidoreductase from Agrobacterium spec.1B was purified 84-fold to apparent homogeneity with 15% recovery, using ammonium sulphate precipitation, heat precipitation, hydrophobic interaction, anion exchange- and gel chromatography. The molecular mass of the native enzyme was estimated to be 320 kDa by gel filtration. SDS-polyacrylamide gel electrophoresis of the enzyme revealed three protein bands corresponding to 85, 35 and 21 kDa. Per molecule the enzyme contains 8 atoms of iron, 8 atoms of acid-labile sulphur, 2 atoms of molybdenum, 2 molecules of FAD and as molybdenum cofactor, molybdopterin cytosine dinucleotide. Besides quinoline-4-carboxylic acid the enzyme also catalysed the conversion of quinoline, 4-chloroquinoline and 4-methylquinoline to the corresponding 2-oxo-1,2-dihydroderivatives. Cyanide, methanol, 4-chloromercuribenzoate and acriflavin were effective inhibitors.