Reaffirmation that metabolism of polyamines by bovine plasma amine oxidase occurs strictly at the primary amino termini.

Oxidation of the biologically important polyamines spermine and spermidine by plasma amine oxidase (PAO) was specified many years ago to occur at the terminal primary rather than internal secondary amine positions. However, the finding of sequential enzymatic conversion of spermine to spermidine and then to putrescine (1, 4-butanediamine) is superficially suggestive of metabolism at the secondary amine positions, and a recent publication (Houen, G., Bock, K., and Jensen, A. L. (1994) Acta Chem. Scand. 48, 52-60) claimed that the original interpretation of preferential "terminal" deamination does not stand up to scrutiny with modern methods of analysis. We herein demonstrate that the findings cited in support of secondary amine deamination can arise artifactually from spontaneous elimination/addition reactions following initial metabolism at the terminal positions of 3-(aminopropyl)amines. We further find no evidence for the ability of PAO to metabolize the secondary amine position in homospermidine, which is devoid of such complicating side reactions. Our results support the original claimed specificity of PAO for the primary amino termini of polyamines, all of which are consistent with the general finding that the quinone-dependent copper amine oxidases specifically metabolize primary amines.