On the amine oxidases of Klebsiella aerogenes strain W70

Klebsiella aerogenes W70 was reported previously to produce a membrane-associated tyramine oxidase (TynA) that did not act on 2-phenylethylamine. Subsequently, a gene cloned from K. aerogenes W70 produced a soluble amine oxidase (MaoA) that acted readily on 2-phenylethylamine and tyramine. This enzyme appeared to be equivalent to a 2-phenylethylamine oxidase of Escherichia coli K-12 (MaoA) but was assumed to be the originally described K. aerogenes W70 tyramine oxidase (TynA). However, as described here, whole cells and cell-free extracts of K. aerogenes W70 showed only the tyramine oxidase (TynA) that is inactive against 2-phenylethylamine and not the maoA gene product. It seems that the organism has two amine oxidase genes, tynA and maoA, but only tynA is expressed. Hence, data relating to the expression of the K. aerogenes W70 tynA gene cannot be assumed to apply to the maoA gene of E. coli K-12 because they encode different enzymes.