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Structural and electrostatic effects on binding of trivalent cations to double‐stranded and single‐stranded poly[d (AT)]
Author(s) -
Plum G. Eric,
Bloomfield Victor A.
Publication year - 1990
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360290105
Subject(s) - spermidine , chemistry , cobalt , crystallography , dna , polynucleotide , counterion , molecule , stereochemistry , inorganic chemistry , ion , biochemistry , organic chemistry , enzyme
We have measured the thermal melting profile for poly[d(AT)] · poly[d(TA)] as a function of concentration of three trivalent cations: spermidine, me 8 spermidine, and hexammine cobalt(III). Using McGhee's (1976) theory of DNA melting in the presence of ligands, we have estimated association constants K h , K c and binding site sizes n h , n c for binding to double‐helical (h) and single‐stranded (c) polynucleotide. The results are as follows:TextCation K h ( M −1 ) n h (bp) K c ( M −1 ) n c (bases)Spermidine 9 × 10 5 2.2 1.3 × 10 4 4.5 Me 8 spermidine 2 × 10 5 1.4 7 × 10 3 3 Hexammine cobalt(III) 1.1 × 10 5 1.5 6 × 10 2 6The binding parameters for spermidine and hexammine cobalt(III) to double helical molecules agree fairly well with direct equilibrium dialysis measurements, and are in reasonable accord with predictions of counterion condensation theory. However, despite their identical charges, the three ligands bind to single‐stranded DNA with quite different affinities. Estimates of the charge spacing of single‐stranded DNA suggest that poly[d(AT)] is less elongated in the presence of spermidine and hexammine cobalt (III) than it is when complexed with me 8 spermidine.