Summary: A novel enzyme which catalyses the decarboxylation of carboxynorspermidine [HN(CH)NHCHCH-CH(NH)COOH] to yield norspermidine [HN(CH)NH], one of the unusual polyamines, was purified to apparent homogeneity (3100-fold) from cells of The enzyme has an apparent of 86000, with a pI of 4·25, and is a dimer composed of identical subunits with an apparent of 43500. The for carboxynorspermidine was 175 μM and for pyridoxal 5′-phosphate, 4·8 μM. The purified preparation had a specific activity of 24·1 μmol norspermidine produced min (mg protein). Carboxyspermidine, a structural homologue, was able fully to replace carboxynorspermidine as a substrate, to produce spermidine, but neither 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, ornithine nor lysine showed detectable substrate activity. The optimum pH was 8·25. Dithiothreitol greatly stimulated the enzyme activity, maximum stimulation being observed at more than 5 mM-dithiothreitol.


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