ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Both Raman spectra and X-ray diffraction patterns have been obtained from oriented fibers of sodium deoxyribonucleic acid (Na-DNA) as a function of salt content and relative humidity. We have confirmed the previously reported X-ray results that, for oriented fibers, the A-form always exists between 75 and 92% relative humidity and that the conformation will change to the B-form at 92% relative humidity only if an excess (3-5%) of added salt is present. Oriented fibers containing low amounts of added salt remain in the A-type conformation at 92% relative humidity and higher. An exact correlation has been found between the familiar A- and B-type X-ray diffraction patterns of DNA fibers and the Raman spectra previously reported without X-ray verification from this laboratory for the A- and B-forms. In particular, a band at 807 cm-1 was always present when a fiber showed the A-type diffraction pattern, and this band shifts to 790 cm-1 in the B-form. Using the Raman spectrum to determine the specific conformation of DNA in samples less amenable to X-ray analysis, we have studied the A ⇄ Btransformation in unoriented fibrous masses of DNA and in concentrated, oriented gels. We find that in unoriented fibrous masses, the A ⇄ B transition always occurs at 92% relative humidity even at very low salt concentration (0-4%). However, in oriented DNA gels at low salt, the A-form can persist as a metastable state to concentration as low as 20% DNA. The origin of the bands at 807 and 790 cm-1 and the possible biological implications of these findings are discussed.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1975.360140613
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