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FAD-containing monoamine oxidase (MAO; EC 1.4.3.4) oxidises monoamines to their corresponding aldehydes, H₂O₂, and NH₃. It has been purified to homogeneity in mammals, but to our knowledge, there have been no reports of the enzyme in plants. MAO activity was detected in Avena sativa seedlings during germination using benzylamine as substrate. The enzyme was purified to homogeneity (as assessed by native PAGE) by Sephadex G-25, DEAE Sephacel, hydroxyapatite, Mono Q, and TSK-GEL column chromatographies. The molecular mass estimated by gel filtration using the TSK-GEL column was 220 kDa. SDS-PAGE yielded four distinct protein bands of 78, 58, 55, and 32 kDa molecular masses. The pI value of the enzyme was 6.3. The enzyme showed high substrate specificity for an endogenous amine, phenethylamine, which was oxidised to phenylacetaldehde, but not for ethylamine, propylamine, butylamine, pentylamine, dopamine, serotonin, tryptamine, or tyramine. The Km values for benzylamine and phenethylamine were 2.7 9 10⁻⁴ and 7.1 9 10⁻⁴ M, respectively. Enzyme activity was not inhibited by pargyline, clorgyline, semicarbazide, or Na-diethyldithiocarbamate. Benzaldehyde, the product of benzylamine oxidation, exhibited strong competitive inhibition of enzyme activity with a Ki of 3 µM. FAD was identified by ODS-column chromatography as an enzyme cofactor. The enzyme contained 2 mol of FAD per 220,000 g of enzyme.
Heavy metal (HM) pollution in aquatic environments is of worldwide concern because of the toxicities of HMs in animals and humans. Constructed wetlands (CWs) have successfully been used as cost-effective natural systems to remove various contaminants. However, the effects of CW on the survival of animals have not been studied in any depth. We established a CW to remove HMs from water in Baiyin City, in the upper Yellow River (YR) region, which has a highly developed mining industry. The HM removal efficiency of CW as well as its effect on the development of the toad Bufo raddei were studied. The HM removal efficiencies by the CW were in the order Cd>Pb>Zn>Cu, and the decrease of the HM concentrations in the water also caused the decrease of the HM concentrations in B. raddei toads living in the CW. The toads in the CW had larger body sizes and less oxidative stress than toads living in the YR, and no malformations were found in the toads living in the CW. These results indicate that CW systems such as that used in this study could protect amphibians from developmental problems caused by HM pollution. We recommend that CW systems are used to treat polluted water and protect amphibians.
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