A Novel Degradation Mechanism for Pyridine Derivatives in Alcaligenes faecalis JQ135

Unlike the benzene ring, the uneven distribution of the electron density of the pyridine ring influences the positional reactivity and interaction with enzymes; e.g., theortho andpara oxidations are more difficult than themeta oxidations. Hydroxylation is an important oxidation process for the pyridine derivative metabolism. In previous reports, theortho hydroxylations of pyridine derivatives were catalyzed by multicomponent molybdenum-containing monooxygenases, while themeta hydroxylations were catalyzed by monocomponent FAD-dependent monooxygenases. This study identified the new monocomponent FAD-dependent monooxygenase HpaM that catalyzed theortho decarboxylative hydroxylation of 5HPA. In addition, we found that themaiA gene coding for maleic acidcis-trans isomerase was pivotal for the metabolism of 5HPA, nicotinic acid, and picolinic acid inA. faecalis JQ135. This study provides novel insights into the microbial metabolism of pyridine derivatives.