MICROBIAL-METABOLISM OF QUINOLINE AND RELATED-COMPOUNDS .18. PURIFICATION AND SOME PROPERTIES OF THE MOLYBDENUM-CONTAINING AND IRON-CONTAINING QUINALDIC ACID 4-OXIDOREDUCTASE FROM SERRATIA-MARCESCENS 2CC-1

Serratia marcescens 2CC-1 utilizes quinaldic acid (quinoline 2-carboxy lic acid) as sole source of carbon, nitrogen and energy. Growth of str ain 2CC-1 on quinaldic acid as well as on nicotinic acid and hypoxanth ine was inhibited completely by the molybdate antagonist tungstate, wh ereas growth on kynurenic acid and 6-hydroxynicotinic acid was not aff ected by tungstate. The synthesis of the molybdenum-containing hydroxy lases quinaldic acid 4-oxidoreductase and nicotinic acid 6-oxidoreduct ase was found to be inducible. In addition, Serratia marcescens 2CC-1 produced a constitutively expressed xanthine oxidoreductase. Quinaldic acid 4-oxidoreductase was purified 1075-fold with a recovery of 5%. F or catalytic activity, artificial electron acceptors were necessary. T he 95-100-kDa enzyme was a heterodimer with subunit molecular masses o f 75-80 kDa and 18-19 kDa. Quinaldic acid 4-oxidoreductase contained 2 .3-3.7 g atom of iron and 0.5-0.6 g atom of molybdenum per mol of enzy me. The absorption spectrum exhibited maxima at 280 nm, 334 nm, 480 nm and a shoulder at 550 nm, with A280/A334 = 4.8, A280/A450 = 10.0, A28 0/A480 = 9.4, and A450/A550 = 1.6, suggesting the absence of a flavin cofactor. Acridine, quinacrine, ethylenediaminetetraacetate, 2,2'-dipy ridyl, 1,10-phenanthroline and iodoacetate did not affect enzyme activ ity. p-Hydroxymercuribenzoate, m-arsenite, cyanide and methanol were e ffective inhibitors of quinaldic acid 4-oxidoreductase. Cyanide-inhibi ted enzyme was reactivated by treatment with S2-, indicating the prese nce of a pterin molybdenum cofactor with a monooxo-monosulfido-type mo lybdenum center. Quinaldic acid 4-oxidoreductase showed a very high su bstrate specificity, quinaldic acid being the only substrate found to be transformed significantly.