Benzylmalonyl-Coa Dehydrogenase, An Enzyme Involved in Bacterial Auxin Degradation

A novel acyl-CoA dehydrogenase involved in auxin degradation in Aromatoleum aromaticum was identified as a decarboxylating benzylmalonyl-CoA dehydrogenase (IaaF). It is encoded within the iaa operon coding for enzymes of auxin catabolism. Using enzymatically produced benzylmalonyl-CoA, the reaction was characterized as simultaneous oxidation and decarboxylation of benzylmalonyl-CoA to cinnamoyl-CoA and CO2. Oxygen served as electron acceptor and was reduced to H2O2, whereas electron transfer flavoprotein or artificial dyes serving as electron acceptors for other acyl-CoA dehydrogenases were not accepted. The enzyme is homotetrameric, contains an FAD cofactor and is enantiospecific in benzylmalonyl-CoA turnover. It shows high catalytic efficiency and strong substrate inhibition with benzylmalonyl-CoA, but otherwise accepts only a few medium-chain alkylmalonyl-CoA compounds as alternative substrates with low activities. Its reactivity of oxidizing 2-carboxyacyl-CoA with simultaneous decarboxylation is unprecedented and indicates a modified reaction mechanism for acyl-CoA dehydrogenases, where elimination of the 2-carboxy group replaces proton abstraction from C2.

Effect of Temperature on Guaiacol Peroxidase of Pyrus communis

Peroxidase (EC 1.11.1.7; donor: hydrogen-peroxide oxidoreductase, POD) is one of the key enzymes controlling plant growth, differentiation and development. The enzyme participates in construction, rigidification and eventual lignification of cell walls, biosynthesis of ethylene from 1-aminocyclopropane-1-carboxylic acid and H2O2, regulation of auxin level through auxin catabolism, protection of tissue from damage and infection by pathogenic microorganisms, the oxidation of indoleacetic acid. For peroxidase activity in wild pears extract one pH optimum was observed at 6.5 that probably belong to atleast one isoenzyme. Activity of peroxidase in presence of guaiacol and H2O2 was optimum after incubation at 40 °C. Maximum activity of peroxidase is 300% .Activity increased to 240%, 300%, 70% and 10% after 60 minute incubation at 30, 40, 45 and 60 °C for peroxidase. Incubation at high temperature (70 °C) was accompanied with decrease of activity to 10% peroxidase activity.

Auxin catabolism and inhibitors in normal and crown gall tissues of Impatiens balsamina

Indoleacetic acid-like substances and hydronaphthoquinoneglucoside concentrations are higher in crown gall and other tissues of infected Impatiens balsamina than in corresponding tissues of non-infected plants.No difference can be found in indoleacetic acid (IAA) synthesizing capacity (from tryptophan) between tissues of normal and tumorous plants.Peroxidase and IAA oxidase in purified extracts of crown gall tissue are higher than in other tissues but only during the first stages of its development. Subsequently, their activity decreases while it continues to increase in leaves and stem.The results suggest participation of IAA oxidase inhibitors, particularly 1,2,4-trihydroxynaphthalene-4-glucoside, in establishing the higher IAA content of crown gall tissues.