| Abstract
| - Ionization of the internucleotidic 2‘-hydroxyl group in RNA facilitates transesterification reactionsin Group I and II introns (splicing), hammerhead and hairpin ribozymes, self-cleavage in lariat-RNA, and leadzymes and tRNA processing by RNase P RNA, as well as in some RNA cleavagereactions promoted by ribonucleases. Earlier, the pKa of 2‘-OH in mono- and diribonucleoside (3‘→5‘)monophosphates had been measured under various nonuniform conditions, which make theircomparison difficult. This work overcomes this limitation by measuring the pKa values forinternucleotidic 2‘-OH of eight different diribonucleoside (3‘→5‘) monophosphates under a set ofuniform noninvasive conditions by 1H NMR. Thus the pKa is 12.31 (±0.02) for ApG and 12.41 (±0.04)for ApA, 12.73 (±0.04) for GpG and 12.71 (±0.08) for GpA, 12.77 (±0.03) for CpG and 12.88 (±0.02)for CpA, and 12.76 (±0.03) for UpG and 12.70 (±0.03) for UpA. By comparing the pKas of therespective 2‘-OH of monomeric nucleoside 3‘-ethyl phosphates with that of internucleotidic 2‘-OHin corresponding diribonucleoside (3‘→5‘) monophosphates, it has been confirmed that the aglyconshave no significant effect on the pKa values of their 2‘-OH under our measurement condition, exceptfor the internucleotidic 2‘-OH of 9-adeninyl nucleotide at the 5‘-end (ApA and ApG), which is moreacidic by 0.3−0.4 pKa units.
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