Putrescine and spermidine are ubiquitous in living organisms. Spermine, third of the three most commonly occurring natural polyamines, is probably present in all eukaryotes but is rare (or nonexistent) in prokaryotes. Polyamine residues are constituents of many compounds found in plants and insects. Putrescine, spermidine, or spermine-containing alkaloids are found in many plants, nonproteinaceous spider and wasp toxins contain polyamine residues, and glutathionyl-spermidine conjugates have been found in some pathogenic microorganisms. In most cells polyamines are the products of a highly...