Diffusion coefficients of the 45S and 50S states of the large ribosomal subunit of E. coli by quasielastic light scattering

The translational diffusion coefficients of the 45S and 50S states of the large ribosomal subunit of E. coli were determined from the spectral distributions of quasielastically scattered light with a 5 mW He-Ne laser as the source. The spectral analysis was performed by directly Fourier transforming the photocurrent and fitting to double-Lorentzian profile via a non-linear regression routine. A small amount (about 1%) of strongly scattering contaminants required the double-Lorentzian profile in order to extract the diffusion coefficients of the principal components. The results are: D 20 °, w(45S) = (1.79 ± 0.12) × 10 -7 cm 2 /sec, and D 20 °, w(50S) = (1.91 ± 0.06) × 10 -7 cm 2 /sec, the latter being in accord with those reported in the literature. The transition from the 50S state to the 45S state is not attended by a change in its molecular weight if the partial specific volumes are assumed to be the same.