Enzymes and pathways of polyamine breakdown in microorganisms

The information currently available on the breakdown of spermidine and putrescine by microorganisms is reviewed. Two major metabolic routes have been described, one for the free bases via δ 1-pyrroline (4-aminobutyraldehyde), the other via N-acetyl derivatives. In both pathways oxidases or aminotransferases are the key enzymes in removing the nitrogen atoms. The two routes converge at 4-aminobutyrate, which is then metabolized via succinate. The degradation of putrescine in Escherichia coli has been well characterized at both genetic and biochemical levels, but for other bacteria much less information is available. The C 3 moiety of spermidine is broken down via β-alanine, but the metabolism of this compound and its precursors is poorly understood. In yeasts, a catabolic route for spermidine and putrescine via N-acetyl derivatives has been described in Candida boidinii, and the evidence for its occurrence in other species is reviewed. Except for the terminal step of this pathway, the same group of enzymes can metabolize both the C 3 and C 4 moieties of spermidine. It is likely that other routes of polyamine catabolism also exist in both bacteria and yeasts.