Phthalate metabolism in Pseudomonas fluorescens PHK: purification and properties of 4,5-dihydroxyphthalate decarboxylase.

Pseudomonas fluorescens PHK uses 4,5-dihydroxyphthalate as the sole carbon source for o-phthalate catabolism. This intermediate is the substrate for a decarboxylase of the pathway yielding protocatechuate. The decarboxylase was purified to homogeneity by an affinity chromatography procedure in which the reaction product, protocatechuate, was used as a ligand. We describe some properties of the enzyme, including its apparent molecular weight of 420,000 as determined by gel filtration and of 66,000 after sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis, consistent with a hexameric functional protein. The apparent Km for the substrate 4,5-dihydroxyphthalate was 10.4 microM. The characteristics of this enzyme are compared with those described for the isofunctional enzyme from P. testosteroni.