Oxidative metabolism of phthalic acid by soil pseudomonads

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Abstract
Protocatechuic acid was detected and identified early in the logarithmic phase of growth in phthalate cultures of Pseudomonas sp. Washed whole cells were sequentially induced to phthalate, 4:5-dihydroxyphthalate and protbcatechuate. Cell-free extracts catalyzed the conversion of 4:5-dihydroxyphthalate, protocatechuate and cis-cis-[beta]-carboxymuconate into 3-oxoadipate. The amounts of gaseous exchange supported data from experiments with whole cells, that the compounds participated in a reaction sequence in that order. Extracts incubated with 4:5-dihydroxyphthalate under anaerobic conditions produced equimolar amounts of CO2 and protocatechuate. After a 5-fold purification of 4:5-dihydroxyphthalic acid decarboxylase, the enzyme showed inhibition by sulphydryl-group reagents and ethylenediaminetetra-acetic acid; the latter effect was partially reversed by Mn and Mg ions. The oxidation of protocatechuate by these extracts proceeded through cis-cis-[beta]-carboxymuconate and 3-oxoadipate, which were isolated. No requirement for ferrous ions could be detected with this protocatechuic acidoxidase.