FURTHER PROPERTIES OF SPERMIDINE DEHYDROGENASE FROM CITROBACTER-FREUNDII IFO 12681

Spermidine dehydrogenase was crystallized for the first time from the cell-free extract of Citrobacter freundii IFO 12681. The enzyme contained one mole of heme b as the prosthetic group and the heme was autooxidizable. Absorption maxima in the visible region were at 561, 530, 428, and 335 nm with the reduced enzyme, while only one peak at 416 nm predominated with the oxidized enzyme. No flavin prosthetic group was detected with the enzyme and PQQ was detected in acid hydrolysate of the enzyme. PQQ appeared to be bound covalently to the enzyme. Thus, the spermidine dehydrogenase of C. freundii has been characterized to be a quinohemoprotein. This is the first instance of amine dehydrogenase in which both heme b and PQQ are involved in enzyme activity.