Oxidative metabolism of phthalic acid by soil pseudomonads

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.