Nucleic Acids Research, 1980, Vol. 8, No. 7 1591-1612
© 1980
Articles |
Structure and dynamics of a tryptophanepeptide-polynucleotide complex
Max-Planck-Institut für Biophysikatische Chemie, D-34 Göttingen, Am Fassberg Postfach 968, GFR
Received February 19, 1980.
The binding of LysTrpLys to single stranded poly(A) was studied by measurements of fluorescence, UV-absorbance, electrodichroism and field jump relaxation. The van't Hoff enthalpy determined at constant degree of peptide protonation is –3.5 kcal/mol (
S = 9 e.u.). The electrodichroism of bound tryptophane residues is negative; its absolute value decreases with increasing degree of binding 
. The magnitude of the dichroism at low indicates a preferential orientation of the tryptophane residues in the plane of the adenine bases, suggesting stacking of Trp with adenine bases. The overall degree of orientation decreases, however, to virtually zero at high . Relaxation measurements at low demonstrate the existence of two steps in the binding reaction of LysTrpLys to poly(A): a fast bimolecular step controlled by diffusion is followed by a slow intramolecular conversion with a forward rate of 1.5 · 103 s–1and a backward rate of 2.7 · 103 s–1. The forward rate is close to that expected for an insertion reaction into stacked poly(A), yet the corresponding stability constant ({small tilde}55) is unexpectedly high.