6-Hydroxynicotinic acid as an intermediate in the oxidation of nicotinic acid by Pseudomonas fluorescens

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Abstract
Washed suspensions of P. fluorescens grown on media containing nicotinic acid oxidize nicotinic acid, 5-fluoronicotinic acid and 2-fluoronicotinic acid at approximately the same rate; 5-chloronicotinic acid is oxidized at a slower rate while neither 5-bromonicotinic acid nor 6-fluoronicotinic acid are oxidized. No intermediates in the oxidation were detected when nicotinic acid or the 5-fluoro and 2-fluoro analogs were substrates. An intermediate was detected during the oxidation of 5-chloronicotinic acid; chromatographic and spectroscopic evidence suggest that the pyridine ring was still intact and that substitution of the [alpha]-carbon atom has occurred. Washed suspensions of cells grown with asparagine oxidize nicotinic acid after a lag period of 90-120 minutes. During the later stages of the lag period, 6-hydroxynicotinic acid was isolated and identified by mixed melting point, chromatographic and spectrographic properties. Cells grown on nicotinic acid oxidize 6-hydroxynicotinic acid without a lag period; 2-hydroxynicotinic acid and alpha-hydroxy pyridine are not oxidized. It is suggested that formation of 6-hydroxynicotinic acid is the first step in the oxidative attack. Cells grown on asparagine adapt to oxidize 6-hydroxynicotinic acid or 5-fluoronicotinic acid. They do not adapt to the other halogen analogs nor to 2-hydroxynicotinic acid, 2:6-dihydroxynicotinic acid or alpha-hydroxy pyridine. Extracts prepared from cells broken in a bacterial press converted nicotinic acid into 6-hydroxynicotinic acid; 6-hydroxynicotinic acid was not oxidized.