Rotational diffusion of Escherichia coli ribosomes. I. - Free 70 S, 50 S and 30 S particles.

The rotational brownian diffusion of Escherichia coli ribosomes has been studied by following the transient dichroism generated by optical excitation of a covalent probe into its triplet state. The induced absorption anisotropy decays exponentially with characteristic correlation times: 2.5 microseconds, 1.6 microseconds and 1.1 microseconds for the 70S ribosome and the 50S and 30S subparticles respectively. The corresponding Stokes radii are in the same order, 133 A, 115 A and 103 A. The hydrodynamic properties are discussed in terms of an ellipsoidal shape of the ribosome particles.