Open AccessDependence of tRNA Structure in Solution upon Ionic Condition of the Solvent
Author(s) -
LABUDA Damian,
HAERTLÉ Tomasz,
AUGUSTYNIAK Jacek
Publication year - 1977
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1977.tb11809.x
Subject(s) - chemistry , titration , fluorescence , transfer rna , binding site , ionic strength , crystallography , binding constant , ligand (biochemistry) , stereochemistry , inorganic chemistry , aqueous solution , biochemistry , receptor , rna , physics , quantum mechanics , gene
Barley phenylalanine tRNA (tRNA phe ) exhibits a 4.7‐fold enhancement of fluorescence intensity in response to the addition of MgCl 2 in 0.01 M Tris‐HCl, pH 7.5, 0.001 M Na 2 EDTA. In the case of 2.0 M NaCl about 60% of this effect was observed. The change of fluorescence intensity was used as a measure of bound ligand concentration. From fluorescence Scatchard plots a different character of Mg 2+ binding to tRNA was revealed, depending upon the initial conformation of tRNA in solution submitted to titration. In NaCl‐free tRNA phe solution strong interacting ( K s = 1.5 × 10 5 M −1 n = 2.4) and weak independent ( K w = 9 x 10 3 M −1 ) Mg 2+ binding were observed. In solution containing 0.1 M NaCl both the strong and the weak Mg 2+ binding demonstrated independent behaviour. K s and K w , in the presence of NaCl, had lower values than in NaCl‐free solution, since Na + was found to be a competitive inhibitor of Mg 2+ binding. Fluorescence titrations of tRNA phe solutions containing Mg 2+ evidenced 2 Na + binding sites/Mg 2+ binding site (at least in the region of weak sites of Mg 2+ ) characterized by inhibitory binding constants K̄ i1 Na = 45 M −1 and K̄ i 1 Na = 8.5 M −1 (mean values) for first and second Na + bindings respectively. Na + exerts a destabilizing effect on tRNA conformation induced by Mg 2+ . A model of Mg 2+ binding and concomitant conformational changes of the tRNA molecule is discussed: one class of Mg 2+ binding sites in unfolded tRNA and two classes of sites, strong and weak, in folded conformation are postulated.