31P-NMRスペクトロスコピーによる分子情報の活用

Nuclear magnetic resonance（NMR）phenomenon discovered by Bloch and Purcell in 1945 is now used in a clinical diagnostic tool as MRI through the imaging technique suggested in 1973 by Lauterbur. Here, we explain 31P-NMR spectroscopy and the method of observing an enzyme reaction velocity in vivo. When phosphorus compounds are placed in a magnetic field, the phosphorus nucleus absorbs and discharges the energy of radio wave at a specific frequency in proportion to the magnetic field intensity. The effective magnetic field on nucleus is reduced by the surrounding electrons, and the shielding effect of the electrons on nucleus causes to reduce the resonance frequency of the nucleus. The shielding effect is expressed as a chemical shift. We can identify molecular structures based on the chemical shifts of resonance lines, and this technique is called an NMR spectroscopy. The phosphorus compounds such as ATP, phosphocreatine and inorganic phosphate can be detected simultaneously and quantified, based on 31P-NMR spectroscopy of living muscle. We can also measure the reaction velocity of creatine kinase, by using the phenomena of saturation and magnetization transfer on 31P-NMR spectroscopy. The nucleus can be placed in a condition of magnetic saturation by the repeated irradiation of the radio wave at the resonance frequency. When the γ phosphate group of ATP is selectively saturated on living muscle, the resonance line of phosphocreatine becomes small, indicating the magnetization transfer from saturated phosphorus atom of γ phosphate group of ATP to phosphorus atom of phosphocreatine. The phosphate exchange reaction is catalyzed by creatine kinase. The flux of the reaction from phosphocreatine to ATP can be calculated with the measurement of the recovery rate from saturation （spin-lattice relaxation time, T1）of phosphocreatine. The applications on perfused heart isolated from bullfrog and also on human heart and chest skeletal muscle in situ were reported. The decreases in both phosphocreatine concentration and the flux of creatine kinase reaction were found in the patients of congestive heart failure.