Premium
B to Z transition in poly(dG‐dC) modified with benzo( a )pyrene diol epoxides studied with polarized light spectroscopy
Author(s) -
Eriksson Magdalena,
Nordén Bengt,
Jernström Bengt,
Gräslund Astrid
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.360290815
Subject(s) - chemistry , polynucleotide , adduct , benzo(a)pyrene , circular dichroism , pyrene , stereochemistry , diol , spectroscopy , crystallography , linear dichroism , polymer chemistry , organic chemistry , biochemistry , physics , quantum mechanics
The NaCl‐induced transition from B to Z conformation in poly (dG‐dC), covalently modified with benzo( a )pyrene diol epoxides (BPDE), has been studied by use of flow linear dichroism (LD), CD, and fluorescence spectroscopy. In contrast to unmodified poly (dG‐dC), the BPDE‐modified polynucleotide displays a B to Z conversion that is incomplete in 2.7 M NaCl. This and a number of other observations are found consistent with a locally retained BPDE perturbed B‐like conformation in the vicinity of the BPDE adduct. In 2.7 M NaCl the polynucleotide orientation in flow is strongly reduced, which could indicate flexibility at the junctions between domains of BPDE perturbed B‐like conformation and Z conformation. A virtually stable high‐salt B form is found in 2.25 M NaCl at 0°C; its CD spectrum resembles that of the transient so‐called B * form, which is observed at an early stage of the B to Z transition. Characteristic B to Z transition times were evaluated by taking this B * ‐form CD spectrum as the initial state spectrum. The kinetics of the B to Z transition, monitored by the CD signal at 287 nm, shows an increased transition rate with (+)‐ anti ‐BPDE modification whereas the (−)‐ anti ‐ and (±)‐ syn ‐BPDE adducts have retarding effects. The difference is discussed against the background of the different binding geometries of the BPDE isomer adducts.