Alternative routes of aromatic catabolism in Pseudomonas acidovorans and Pseudomonas putida: gallic acid as a substrate and inhibitor of dioxygenases

Abstract

When 3,4 dihydroxyphenylacetic acid (homoprotocatechuic acid) was added to P. acidovorans growing at the expense of succinate, enzymes required for degrading homoprotocatechuate to pyruvate and succinate semialdehyde were strongly induced. These enzymes were effectively absent from cell extracts of the organism grown with 4 hydroxyphenylacetic acid, and this substrate was metabolized by the catabolic enzymes of the homogentisate pathway. Two separate fission dioxygenases for 3,4,5 trihydroxybenzoic acid (gallic acid) were present in cell extracts of P. putida when grown with syringic acid, and gallate was degraded by reactions associated with meta fission. One of the two gallate dioxygenases also attacked 3 O methylgallic acid; the other, which did not, was induced when cells were exposed to gallate. This organism possessed ortho fission enzymes, including protocatechuate 3,4 dioxygenase (EC 1.13.11.3) and cis,cis carboxymuconate lactonizing enzyme (EC 5.5.1.2), after induction with 3,4 dihydroxybenzoic acid (protocatechuic acid). Gallate was a substrate for protocatechuate 3,4 dioxygenase, with a V(max) about 3% of that of protocatechuate and with an apparent K(m) slightly lower. Gallate was a powerful competitive inhibitor of protocatechuate oxidation.