title: Dependence of tRNA structure in solution upon ionic condition of the solvent. Fluorescence studies of monovalent cation binding to tRNAPhe from barley embryos.
abstract: Dependence of barley phenylalanine tRNA (tRNAPhe) fluorescence intensity at 430 nm upon LiCl, NaCl, KCl, CsCl or NH4Cl concentration was measured in 0.01 M Tris-HCl, pH 7.5, 0.001 M Na2EDTA solutions. Increase of monovalent cation concentration in the solvent from 0 to 2 M induced about 3-fold fluorescence intensity enhancement. The fractional fluorescence change was used as a measure of bound ligand concentration. Fluorescence Scatchard plots revealed three classes of monovalent cation binding sites on the tRNA molecule: interacting (strong) and independent (weak and very weak) sites. Calculated from Scatchard plots binding constants (K), for strong and weak binding of monovalent cations (in the case of Na+ binding: Ks = 26 M-1 and Kw = 4.3 M-1 respectively) exhibit linear dependence upon ionic radius (r). Two limiting values obtained from the plot of K versus r: K(max) at r = 0 r(max) at K = 0, characterize additionally strong and weak monovalent cation binding sites (Ks(max) = 42 M-1 Kw(max) = 8.5 M-1, rs(max) = 0.23 nm and rw(max) = 0.22 nm). A model of the relationship between weak Mg2+ binding sites and monovalent cation binding sites as well as of monovalent cations binding to tRNA is proposed.
mesh_terms: D002414:Cations, Monovalent; D055598:Chemical Phenomena; D002621:Chemistry; D001467:Hordeum; D007700:Kinetics; D008274:Magnesium; D009690:Nucleic Acid Conformation; D010649:Phenylalanine; D012343:RNA, Transfer; D012997:Solvents; D013050:Spectrometry, Fluorescence
chemical_list: D002414:Cations, Monovalent; D012997:Solvents; D010649:Phenylalanine; D012343:RNA, Transfer; D008274:Magnesium