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Studies on conformational changes in the DNA structure induced by protonation: Reversible and irreversible acid titrations and sedimentation measurements
Author(s) -
Zimmer Ch.,
Triebel H.
Publication year - 1969
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.1969.360080503
Subject(s) - protonation , chemistry , titration , denaturation (fissile materials) , dna , sedimentation coefficient , acid–base titration , crystallography , helix (gastropod) , titration curve , transition (genetics) , inorganic chemistry , biochemistry , organic chemistry , nuclear chemistry , biology , snail , gene , ion , ecology , enzyme
Reversible and irreversible conformational changes in the acid‐induced denaturation of DNA were studied by spectrophotometric titration, sedimentation, and melting measurements. A GC‐rich DNA (72 mole‐%) shows complete or partial reversibility of the titration profiles within the pH region of transition from helix to coil, while AT‐rich DNA (29 mole‐%) is irreversible in its titration behavior at each acid pH below the onset of the transition. The results for GC‐rich DNA further indicate distinct differences in the titration behavior, which can be attributed to differences in the frequency of GC clusters along the DNA molecule. Plots of the sedimentation coefficient and the parameter a s app against pH lead to the conclusion that conformational changes occur before the onset of the acid‐induced helix–coil transition. These alterations are more pronounced upon protonation of larger GC‐rich domains than of smaller ones, as concluded from very marked differences observed in the sedimentation–pH behavior of two GC‐rich DNA's. An acid denaturation scheme for a GC‐rich DNA segment is suggested. Reversibility of the acid denaturation is explained by the existence of stable, protonated, single GC base pairs in nonprotonated stacked single‐stranded domains formed in the acid‐induced transition region.