Summary: Dimethylamine dehydrogenase was purified 15.6-fold from X grown anaerobically on dimethylamine as sole carbon source by ammonium sulphate fractionation and chromatography on DEAE-cellulose. The preparation was free from trimethylamine dehydrogenase. The molecular weight of the enzyme was 176 000 and subunit analysis by sodium dodecyl sulphate–polyacrylamide gel electrophoresis indicated that it consists of two, probably identical, subunits with molecular weights of 91 000. The absorption spectrum showed a maximum at 441 nm. Reduction of the enzyme with dimethylamine produced a new absorption maximum at 356 nm, while the absorption at 441 nm decreased. The pH optimum for the oxidation of dimethylamine was 8.1. In this reaction, stoicheiometric amounts of methylamine and formaldehyde were formed as products. The enzyme showed absolute specificity towards secondary amines; dimethylamine, methylethylamine, diethyl-amine, methylpropylamine, ethylpropylamine and methylethanolamine were oxidized while primary and tertiary amines and quaternary ammonium salts were not. Apart from phenazine methosulphate, only phenazine ethosulphate, Wurster's blue and methylene blue served as artificial electron acceptors. The apparent of the enzyme for dimethylamine at pH 7.7 was 15.6. 1.6 μ Trimethylamine was a potent competitive inhibitor of dimethylamine oxidation with an apparent of 7.1 μ This inhibition of dimethylamine dehydrogenase by trimethylamine probably explains the observed accumulation of dimethylamine during anaerobic growth of X on trimethylamine.


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