Co-operative non-enzymatic base recognition III. Kinetics of the helix—coil transition of the oligoribouridylic · oligoriboadenylic acid system and of oligoriboadenylic acid alone at acidic pH

摘要: Abstract The kinetics of the transition from a double helix to random coil have been investigated for oligoadenylic · oligouridylic acid at neutral pH and acidic pH. oligoadenylic—oligouridylic system has studied by temperature-jump stopped-flow method. Two different types helix—coil transitions observed: (1) transition, characterized single relaxation time (except in case long chains), (2) triple with process which is slower factor about 100. These processes were followed characteristic changes u.v. spectrum A U ratios. Conditions found where could be observed without interference triple-stranded helices. measured chain lengths 8, 9, 10, 11, 14 18. rate constants formation are 106 M−1 sec−1 associated negative apparent activation enthalpies −9 kcal./mole. rates dissociation given temperature become smaller increasing length. At constant length increase temperature. corresponding larger longer chains (N = AED 30 kcal./mole; N 18, 93 kcal./mole). greater an additional observed. This due unzippering equilibrium ends too fast analysis Some measurements tetradeca- octadeca-nucleotides also demonstrate that proceeds as second-order reaction recombination enthalpy can process. second order sec−1, value being almost independent decreases increases energy −6 performed three degrees transition. degree same all lengths. Increasing temperatures lead dissociation; oligonucleotide. detailed these results elucidation elementary steps. It concluded helical nucleus rate-determining step recombination. From values it shown base pairs form stable nucleus. According this result, least two nucleation parameters needed: one first pair another pair. adjacent proceed 107 sec−1. demonstration consisting interesting respect evolution triplet genetic code. codon-anticodon interaction via triplets provides combination accurate recognition (stable pairing) high dynamic flexibility.