The A76 or A73 nucleotide at the 3'end of tRNAPhe was modified with the fluorescent reagent of proflavine (PF). The distance between the fluorophore of the 3'end and the Y base was measured by singlet-singlet energy transfer under the conditions of 10 mM and 0.01 mM Mg2+. The distance obtained at 10 mM Mg2+ is very close to that obtained by the X-ray diffraction method, while the distance at 0.01 mM Mg2+ is significantly smaller. The difference in the distance is explained as a result of destabilization of the tertiary structure with reduction of the Mg2+ concentration. The calculated distance between A73 and A76 shows the stacked conformation of the CCA strand. Fluorescent quenching experiments showed that the degree of stabilization of 3'end A76 by stacking is lower than that of A73. The removal of the CCA segment causes a difference not only in the thermal melting curves but also in the fluorescent wavelength of the Y base at 0.01 mM Mg2+. The results suggest that the 3'end CCA strand has a helical structure and contributes to the stabilization of the whole structure of tRNAPhe.

The pathogenesis of bronchial asthma is not yet fully understood. Recently much attention has been given to the hypothesis that intracellular free calcium ([Ca2+]i) metabolism is abnormal in various diseases. In this study weinvestigated whether [Ca2+]i exists abnormally in subjects with bronchial asthma. The [Ca2+]i in 32 treated or untreated subjects with bronchial asthma were compared with 63 normal subjects. Resting levels of [Ca2+]i were estimated by loading the fluorescent indicator Fura-2 in washed platelets. The [Ca2+]i level in the control subjects was 129.7+18.0 nM(mean±SD). However, in that of the bronchial asthma patients was 152.7+44.1 nM, significantly higher than that of the control subjects (p<0.05). It is well recognized that an increase of [Ca2+]i in vascular smoothmuscle involves contraction. The findings suggest that the same phenomenon is quite possible in the tracheal smooth muscle and that it plays an important role in the pathogenesis of bronchial asthma. (Internal Medicine 34: 722-727, 1995)

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