A novel enzyme which catalyses the decarboxylation of carboxynorspermidine [H2N(CH2)3NHCH2CH2CH(NH2)COOH] to yield norspermidine [H2N(CH2)3NH(CH2)3NH2], one of the unusual polyamines, was purified to apparent homogeneity (3100-fold) from cells of Vibrio alginolyticus. The enzyme has an apparent M(r) of 86000, with a pI of 4.25, and is a dimer composed of identical subunits with an apparent M(r) of 43500. The K(m) 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-1 (mg protein)-1. 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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