Proton and phosphorus-31 magnetic relaxation studies on the interaction of polyriboadenylic acid with Mn2+

✍ Scribed by Atsuko Yamada; Kazuyuki Akasaka; Hiroyuki Hatano

• Publisher: Wiley (John Wiley & Sons)
• Year: 1976
• Tongue: English
• Weight: 844 KB
• Volume: 15
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1976.360150708

✦ Synopsis

Proton and phosphorus-31 nuclear spin-lattice relaxation times 2' 1 and spin-spin relaxation times T2 have been measured on the single-stranded polyriboadenylic acid [poly(A)]-Mn2+ system in a neutral D2O solution in the temperature range 10"-90"C a t 100 and 40.5 MHz, respectively, with the Fourier transform nmr method. Minimum values of T I have been found for all these nuclei, which have enabled the exact estimation of apparent distances from Mn2+ to H2, Hs, HI,, and the phosphorus nucleus to be 4.7,4.1, 5.2, and 3.0 A, respectively. The electron spin of Mn2+ penetrates into the phosphorus nucleus, giving 31P hyperfine coupling of more than lo6 Hz. Evidence of penetration of the electron spin into H g and H2 is also obtained, suggesting direct coordination of nitrogen atoms of the adenine ring to the Mn2+ ion. Combined with the result from proton relaxation enhancement of water, it is concluded that every Mn2+ ion added is bound directly to two phosphate groups with a Mn2+-phosphorus distance of 3.3 A, while a part of the Mn2+ ions are simultaneously bound to the adenine ring.

It is estimated that 39 f 13% and 13 f 5% of Mn2+ are coordinated by N7 and N3 (or NI), respectively. The motional freedom of poly(A) in the environment of the Mn2+ binding site has been found to be quenched to the extent that the rotational motion becomes several times slower than that of the corresponding Mn2+-free poly(A). The activation energies for the molecular motion are, however, practically unchanged from those for Mn2+-free poly(A),