生体分子交換反応の研究におけるNMR飽和移動(Saturation transfer)法の利用

概要

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The substance exchanging between two chemically different sites A and B gives two separate NMR signals at νA and νB, if the exchange rate is slower enough than the frequency separation ΔνAB. When the sample is irradiated at the frequency νB, the signal intensity of A occasionally becomes weaker or disappears. This phenomenon is called saturation transfer in NMR and is used to determine the sites and rate of the exchange process. This technique is only applicable when the life time of exchange is between the inverse of ΔνAB and the spin lattice relaxation time T1.<BR>By using this technique we found that there is direct proton exchange between the complementary nucleic acid bases in organic solvents. When the signal of the amino protons of an adenine derivative is irradiated, the imino proton signal of an uracil derivative disappears. By quantitative analysis following the Forsen and Hoffman's treatment, it was found that the exchange occurs ten times in a second at room temperature.<BR>Other applications related to biological systems are reviewed: the electron exchange between cytochromes and the proton exchange between peptides and solvent water. The rates of following reactions were examined: the synthesis of ATP from AMP and inorganic phosphate by ATPase, the disproportionation of two ADP to ATP and AMP by adenylate kinase and the hydroxylation of acetylaldehyde by carbonic anhydrase.
日本生物物理学会の論文