Evidence obtained from experiments with rats and mice is presented suggesting that the naturally occurring amino acids putreanine and N8-(2-carboxyethyl)spermidine, and most probably also related compounds deriving from the polyamines spermidine and spermine by oxidative metabolism, are formed within two anatomical compartments. In the first step polyamines are converted into aldehydes by serum spermine oxidase in the circulation. A certain portion of these aldehydes can be taken up by liver and other organs and transformed by aldehyde dehydrogenase into the corresponding amino acids. Putreanine is not only derived from spermidine, but can also be formed from N8-(2-carboxyethyl)spermidine by oxidative deamination, catalysed by serum spermine oxidase, and subsequent spontaneous elimination of acrolein.
