Mandelic acid-4-hydroxylase, a new inducible enzyme from Pseudomonas convexa

Microbial metabolism of mandelate: a microcosm of diversity

This review highlights the diversity of prokaryotic and eukaryotic microorganisms that can metabolise mandelate and it describes how a wide range of compounds related to mandelate is formed in many environments. The chief aspects that are summarised include the various pathways whereby mandelate and its structural analogues are converted into catechol or protocatechuate, the properties of the enzymes that are involved in the pathways, and the regulation and genetics of the pathways. The review incorporates the idea that the study of peripheral metabolic pathways is particularly useful for illuminating evolutionary speculations and it concludes with a list of questions that need to be answered.

Purification and properties of L-4-hydroxymandelate oxidase from Pseudomonas convexa

An inducible membrane-bound L-4-hydroxymandelate oxidase (decarboxylating) from Pseudomonas convexa has been solubilized and partially purified. It catalyzes the conversion of L-4-hydroxymandelic acid to 4-hydroxybenzaldehyde in a single step with the stoichiometric consumption of O2 and liberation of CO2. The enzyme is optimally active at pH 6.6 and at 55 degrees C. It requires FAD and Mn2+ for its activity. The membrane-bound enzyme is more stable than the solubilized and purified enzyme. After solubilization it gradually loses its activity when kept at 5 degrees C which can be fully reactivated by freezing and thawing. The Km values for DL-4-hydroxymandelate and FAD are 0.44 mM and 0.038 mM respectively. The enzyme is highly specific for DL-4-hydroxymandelic acid. DL-3,4-Dihydroxymandelic acid competitively inhibited the enzyme reaction. From the Dixon plot the Ki for DL-3,4-dihydroxymandelic acid was calculated to be 1.8 X 10(-4) M. The enzyme is completely inactivated by thiol compounds and not affected by thiol inhibitors. The enzyme is also inhibited by denaturing agents, heavy metal ions and by chelating agents.

Involvement of 4-hydroxymandelic acid in the degradation of mandelic acid by Pseudomonas convexa

A microorganism capable of degrading DL-mandelic acid was isolated from sewage sediment of enrichment culture and was identified as Pseudomonas convexa. It was found to metabolize mandelic acid by a new pathway involving 4-hydroxymandelic acid, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, and 3,4-dihydroxybenzoic acid as aromatic intermediates. All the enzymes of the pathway were demonstrated in cell-free extracts. L-Mandelate-4-hydroxylase, a soluble enzyme, requires tetrahydropteridine, nicotinamide adenine dinucleotide phosphate, reduced form, and Fe2+ for its activity. The next enzyme, L-4-hydroxymandelate oxidase (decarboxylating), a particulate enzyme, requires flavine adenine dinucleotide and Mn2+ for its activity. A nicotinamide adenine dinucleotide-dependent, as well as a nicotinamide adenine dinucleotide phosphate-dependent, benzaldehyde dehydrogenase has been resolved and partially purified.