Letter | Published:

Molecular Weights and Physical Properties of Deoxyribonucleic Acid

Naturevolume 180page1340 (1957) | Download Citation



IN the measurements of the molecular weight from light scattering and of other physical properties of deoxyribonucleic acid, an extraordinary variety of results has been obtained1, even with samples prepared from a single source, namely, calf thymus. To some extent this might be accounted for as a result of fractionation of the material resulting from its physical heterogeneity, which has been demonstrated by Shooter and Butler2, and by Schachman et al. 3. It may also arise from small amounts of protein impurity, which have been shown4 to affect the physical properties to a marked extent. In order to reduce the sources of discrepancy, it has been thought desirable to determine (1) light scattering, (2) intrinsic viscosity, (3) sedimentation coefficients, on identical solutions of calf thymus deoxyribonucleic acid treated in various ways. It has been found that centrifuging as a means of clarifying the solutions is made much more effective by reducing the concentration from 0.1 to 0.04 per cent. Table 1 shows the effect of centrifuging for 18 hr. at 20,000g at these two concentrations. The difference must be due to the greater viscosity of the stronger solution. The light-scattering molecular weight, especially of the more turbid samples, is markedly reduced by centrifuging in this way at the lower concentration, without any great change of either the intrinsic viscosity or of the sedimentation coefficients. This must mean that the component which gives rise to high turbidities in the unclarified solutions does not contribute appreciably to the viscosity and sedimentation coefficient. That the high turbidities of the unclarified solutions is not due to deoxyribonucleic acid has been demonstrated by the fact that the action of deoxyribonuclease on a clarified solution (J40) with molecular weight 4×106 reduced the light scattering to 20 per cent of its original value ; while on a turbid solution (J38), having an apparent molecular weight of 17×106, the light scattering value was reduced by only 40 per cent, that is, to 10×106.

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  1. 1

    Reichmann, M. E., Rice, S. A., Thomas, C. A., and Doty, P., J. Amer. Chem. Soc., 76, 3047 (1954). Sadron, C., Rep. 3rd Int. Cong. Biochem. (Brussels), 210 (1955). Brown, G. L., McEwen, M. B., and Pratt, M. I., Nature, 176, 161 (1955).

  2. 2

    Shooter, K. V., and Butler, J. A. V., Trans. Farad. Soc., 52, 734 (1956).

  3. 3

    Schumaker, V. N., and Schachman, H. K., Biochim. Biophys. Acta, 23, 628 (1957).

  4. 4

    Butler, J. A. V., Phillips, D. M. P., and Shooter, K. V., Arch. Biochem. (in the press).

  5. 5

    Mandelkern, L., Krigbaum, W. R., Scheraga, H. A., and Flory, P. J., J. Chem. Phys., 20, 1392 (1952).

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  1. Chester Beatty Research Institute, London, S.W.3.

    • J. A. V. BUTLER
    • , D. J. R. LAURENCE
    • , A. B. ROBINS
    •  & K. V. SHOOTER


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