Characterization of heterogeneous solutions using laser light scattering: study of the tubulin system

Laser light scattering has been applied to a systematic study of a heterogeneous solution of tubulin at low temperature--conditions under which tubulin assembly into microtubules does not take place. Methods of analyzing laser light scattering results obtained from solutions containing multiple components are discussed. Data analysis techniques are described and their application to the determination of diffusion constants from experimental data is extensively illustrated. Multiple components were found under the conditions that the tubulin was studied. We have identified one component having D20,w = 4.41 X 10(-7) cm2/s (sigma = 0.54 X 10(-7) cm2/s) which has the expected value for tubulin dimer. In addition, we have found two components which are significantly larger than tubulin. One large component has D 20,w approximately 0.55 X 10(-7) cm2/s and is present in all samples at 4 degrees C even after centrifugation to remove components greater than 10 S. Another large component having 3.2 X 10(-7) cm2/s greater than or equal to D20,w greater than or equal to 1.5 X 10(-7) cm2/s has been found to sediment with 10 S less than or equal to s less than 20 S.