The heterogeneity of amine oxidase with Rhodoccus opacus
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Four native amine oxidases have been identified from Rhodococcus opacus to reveal phenotypic plasticity and catalytic activity with respect to structurally diverse natural and synthetic amines. Altering the amine growth substrate enabled tailored and targeted oxidase upregulation, facilitating catalytic differentiation and isolation. Each enzyme was purified over 80 fold by chromatography, allowing subsequent characterisation. Two oxidases possessed a copper dependent redox co-factor with broad specificity towards monoamines. Michaelis constants (KM) ranged from 0.1 to 0.9 mM for common C1–C5 aliphatic monoamines and <0.2 mM for a range of aromatic amines. The remaining two oxidases by contrast were highly specific for aliphatic diamines, with a Michaelis constants (KM) = 60 μM for putrescine by a third copper oxidase and a (KM) = 190 μM by a flavin dependent oxidase. MALDI-TOF and genomic analysis has indicated metabolic gene clusters, multiple gene activation, and complex biodegradation pathways. With a consideration of the diamine acting oxidase, a putrescine degradation pathway is confirmed that utilises oxidases in tandem with a 4-aminobutyraldehyde dehydrogenase. The taxonomic distribution of this pathway is further examined utilising phylogenetic analysis. Oxidase regulation and integration into the nitrogen cycle is then considered, with implications in bioremediation and biocatalysis discussed.