Abstract
WE found1 that the molecular weight of deoxyribonucleic acid from herring sperm heads, measured by light-scattering in dilute aqueous solution, was reduced from 6 × 106 to 3 × 106 on adding a concentrated urea solution to make the final urea concentration 4 M. This halving of the molecular weight was accompanied by a 20 per cent increase in the radius of gyration of the coil. This behaviour is consistent with the twin spiral model of Crick and Watson2 if it is assumed that the urea splits the hydrogen bonds holding the two molecules together. After removal of the urea by dialysis the ‘split’ molecule coils up into a much more compact shape1; if the dialysis is conducted from solutions containing less than 0.003 per cent deoxyribonucleic acid, the molecular weight remains unchanged at 3 × 106; in more concentrated solutions aggregation occurs and molecular weights ranging up to 2 × 107 have been measured.
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References
Alexander, P., and Stacey, K. A., Trans. Farad. Soc., 50, 303 (1954); Biochem. J., 60, 194 (1955).
Crick, F. H. C., and Watson, J. D., Nature, 171, 737 (1953); Proc. Roy. Soc., A, 223, 80 (1954).
Doty, P., and Rice, S. A., Biochim. Biophys. Acta, 16, 446 (1955).
Butler, J. A. V., Conway, B. E., and James, D. W. F., Trans. Farad. Soc., 50, 612 (1954).
Jungner, G., Science, 113, 378 (1951).
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ALEXANDER, P., STACEY, K. Dissociation of Deoxyribonucleic Acid by Urea. Nature 176, 162–163 (1955). https://doi.org/10.1038/176162a0
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DOI: https://doi.org/10.1038/176162a0
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