Catalyzes the decarboxylation of carboxynorspermidine and carboxyspermidine. 2,3-diaminopropionic acid, 2,4-diaminobutyric acid, L-ornithine or L-lysine cannot serve as substrates. carboxynorspermidine + H(+) = CO2 + norspermidine carboxyspermidine + H(+) = CO2 + spermidine Dithiothreitol greatly stimulates activity, maximum stimulation being at 5-20 mM dithiothreitol concentration. Fe(3+), Fe(2+) and Mn(2+) severely inhibit activity (88%, 82% and 50%, respectively), whereas Zn(2+) has a slightly inhibitory effect (23%) and Mg(2+), Ca(2+), Cu(2+) and Cu(+) have no effect. Optimum pH is 8.25. Stable at pH 7.5 and 4 degrees Celsius in the presence of DTT, EDTA and NaN(3) for at least one month. 57% and 72% of the maximum activity observed at pH 7.5 and 9.0, respectively. Optimum temperature is 37 degrees Celsius. 75% and 51% of the maximum activity remains at 30 and 45 degrees Celsius, respectively, but the activity decreases rapidly at temperatures above 55 or below 20 degrees Celsius. Homodimer. Belongs to the Orn/Lys/Arg decarboxylase class-II family. NspC subfamily.