Porphyrin induced Z to B conversion of poly(dG-dC)2 in ethanol.
The water soluble porphyrins H2TMpyP-2, H2TMpyP-4, and CuTMpyP-4 are found to bind to Z-form poly(dG-dC)2 in 60% ethanol (v/v) and to facilitate the conversion of the polymer to the B form. Metalloporphyrins with axial ligands (MnTMpyP-4, ZnTMpyP-4) interact to some degree with the Z form, but do not lead to extensive conversion to the B form. The conversion of the Z form into the B form was determined by CD titration experiments, which were used to quantitate the fraction of poly(dG-dC)2 present in each conformation. Under all conditions each bound porphyrin molecule converts multiple base pairs from Z to B. The kinetics of porphyrin reactions with Z-poly(dG-dC)2 in 60% ethanol were measured using two different detection techniques. Stopped flow spectrophotometry was used to observe the time-dependent spectral changes associated with the porphyrins during the reaction. Time-dependent changes in the poly(dG-dC)2 conformation were observed directly using CD. The porphyrin absorbance changes under the conditions of these experiments have a much shorter half time (t1/2 approximately 0.1 to 2 sec) than the CD changes (t1/2 approximately 10 sec). Thus it could be determined that a complex with spectral characteristics similar to those of the porphyrin intercalated into B-form poly(dG-dC)2 is produced while the polymer is predominantly in the Z form.
McKinnie
R E
RE
Department of Chemistry, Swarthmore College, PA 19081.
Choi
J D
JD
Bell
J W
JW
Gibbs
E J
EJ
Pasternack
R F
RF
D002942:Circular Dichroism; D000431:Ethanol; D007700:Kinetics; D011089:Polydeoxyribonucleotides / Q000138:chemical synthesis*; D011108:Polymers; D011166:Porphyrins; D011487:Protein Conformation; D013816:Thermodynamics
D011089:Polydeoxyribonucleotides; D011108:Polymers; D011166:Porphyrins; C019530:poly(dC-dG); D000431:Ethanol