Oxidative metabolism of naphthalene by soil pseudomonads. The ring-fission mechanism

Abstract

Naphthalene is oxidatively metabolized by soil pseudomonads through D-trans-l,2-dihydro-l,2-dihydroxynaphthalene to 1,2-dihydroxynaphthalene, which then undergoes ring-cleavage. The immediate product of ring-fission is cis-o-hydroxybenzalpyruvate, isolated as the crystalline perchlorate. The Fe2+ ion-dependent oxygenase therefore disrupts the bond between the angular C and C-1 of the naphthalene nucleus. Some properties of cis-o-hydroxybenzalpyruvate are described. Under alkaline conditions it exists as the open-chain cis-yellow anion, the real intermediate in the metabolic pathway. At neutral or slightly acid pH, cyclization to the hemiacetal form occurs; in strong acid it exists as the yellow pyrilium cation. trans-o-Hydroxy-benzalpyruvate is obtained by isomerization of the enzymically prepared cis-form, and by chemical synthesis. Both are converted without gaseous exchange into salicylaldehyde and a fragment tentatively identified as pyruvate, by an enzyme system of an aldolase type isolated from the bacteria. A nicotinamide-adenine-dinucleotide (NAD)-specific dehydrogenase present in the cell-free extract oxidizes the salicylaldehyde to salicylate. The latter is then oxidatively decarboxylated to catechol, which is completely dissimilated through a-hydroxymuconic semialdehyde. All the naphthalene-utilizing microorganisms so far examined use this pathway.