Interaction of sulfur-containing radioprotectors with DNA: a spectrophotometric study

The interaction between sodium-compensated DNA and several aminothiol radioprotectors [cysteamine; methyl-2-cysteamine; cysteamine phosphorothioate; N-(2-mercaptoethyl) 1,2-diaminoethane; N-(2-mercaptoethyl)-1,3-diaminopropane; N-(3-aminopropyl)-2-aminoethyl phosphorothioic acid] has been studied by spectrophotometry. In all cases, elevation of the melting point (Tm) of the DNA-radioprotector complex was observed. The interaction of these ionized aminothiols with phosphate groups of DNA is essentially an electrostatic one, like that for metallic cations, and can be expressed by the Schildkraut-Lifson equation Tm = a log Cradio + b, where a and b are adjustable parameters and Cradio is the concentration of the radioprotectors.