Electron spin resonance in ATP and RNA.

Cu(++), Mn(++), and Fe(+++) account for the electron spin resonances observed in certain samples of ATP and RNA. The copper ion seems more loosely bound to these substances than either iron or manganese. A striking similarity is observed between the manganese spectra in manganese RNA, ATP, and ADP suggesting that the binding sites are similar in the three compounds. The similarity of the e.s.r. spectra of iron ATP and of iron and manganese RNA, except for hyperfine spectrum (hfs) in the latter, suggests that the two ions bind similarly in the two compounds. A detailed interpretation of the spectra is lacking however and these conclusions can only be tentative. When manganese TPP and ATP are heated or pH changed the e.s.r. alters indicating a change in the environment of the ion. The sharp 6 line manganese spectrum in both TPP and ATP at pH 1 suggests an almost "free" ion at this pH in the sense of an almost isotropic average environment.