FIG. 1.
Proposed pathway for degradation of PNP by Arthrobacter sp. strain JS443. Hypothetical intermediates are indicated by brackets. The pathway encoded by the npd gene cluster proceeds through 1,4-benzoquinone and hydroxy-1,4-benzoquinone, as shown in this study. In strain JS443, an unknown oxygenase diverts an unknown proportion of PNP to 4-nitrocatehcol (20), which reenters the npd pathway after being oxidized by NpdA2. Accumulation of hydroquinone (presumably through reduction of 1,4-benzoquinone) was observed by Jain et al. (20) and in the current study, but its fate is unknown. Hydroquinone is not metabolized by either NpdA2 or NpdB. FADH2, reduced flavin adenine dinucleotide.