Nuclear Magnetic Resonance Study of Hydrogen-Bonded Ring Protons in Watson-Crick Base Pairs

摘要

We have studied the low-field proton magnetic resonance spectrum of the double-helical complex of d(A-A-C-A-A) with d(T-T-G-T-T). Well-resolved resonances for the thymidine N3 and the guanosine N1 protons are seen at 1°C, which broaden by 4°C and disappear above 9°C. The actual Tm of the complex was found to be 28°C by measurement of UV-absorbance change. There are several factors that could limit the observed exchange broadening of the resonance lines; the model that best fits the data is one in which the rate of double-helix dissociation limits the rate of exchange of the H-bonding protons with water.