Studies on the interaction of homologues of spermine with deoxyribonucleic acid and with bacterial protoplasts

Four homologues of the naturally occurring polyamine spermine, of the type H2N*[CH2]3*NH* [CH2].*NH*[CH2]s *NH2 where n= 2, 3, 5 and 6, have been synthesized. Their ability to stabilize E8cherichia coli protoplasts against osmotic lysis was compared with that of spermine. All homologues were approximately as effective as spermine. The effect of low concentrations of the homologues on the Tm of calf thymus DNA and of Aerobacter aerogenes DNA in 0 03M-sodium chloride- 1mM-potassium dimethylglutarate buffer, pH 6-2, was tested. The increase in Tm for a given concentration of amine was found to be n= 5 > n= 4 and n= 6 > n= 3> n= 2. When calf thymus DNA in 0'15M-sodium chloride-l5mM-sodium citrate was used spermine gave the highest increase in Tm. It is concluded that the stabilization of E. coli protoplasts by tetra-amines is a non-specific effect inde- pendent of chain length, whereas the elevation of Tm of DNA is a more specific effect which depends on chain length. * Abbreviations: 3-2-3-tetra-amine, NN'-bis-(3'-aminopropyl)-1,2-diaminoethane; 3-3-3-tetra-amine, NN'-bis-(3'-aminopropyl)-1,3-diaminopropane; 3-5-3-tetra-amine, NN'-bis-(3'-aminopropyl)-1,5-diaminopentane; 3-6-3-tetraamine, NN'-bis-(3'-aminopropyl)-1,6-diaminohexane; 2-2-2-tetra-amine, NN'-bis-(2'-aminoethyl)-1,2-diaminoethane; 2-2-triamine, N-2'-aminoethyl-1,2-diaminoethane; Tm (melting temperature), the temperature at which 50% of the total increase in E260 has occurred.