Mechanism of toxicity of putrescine in Anacystis nidulans.

Putrescine is lethal to the cyanobacterium Anacystis nidulans at extracellular pH values at which significant concentrations of the nonprotonated diamine rapidly diffuse into the cell and accumulate as the charged form. Although over 98% of the accumulated putrescine is not metabolized, a small fraction is rendered trichloroacetic acid-insoluble, and about 90% of this is bound as putrescinie to proteins and cell structures. Various synthetic functions were studied in the presence of a bacteriostatic (40 microM) and a bacteriocidal (150 microM) concentration of putrescine at pH 9.5. Under lethal conditions, protein synthesis was completely inhibited after 45 min and CO2 fixation after 100 min, whereas nucleic acid synthesis was less affected. Spermidine was lost from the cell and its synthesis was arrested. These functions were much less inhibited at 40 microM putrescine. Ribosomes from putrescine-killed cells were found to be irreversibly dissociated into 30S and 50S subunits. Some putrescine (1-4 molecules) cosedimented with each subunit.