Equilibrium components of tubulin preparations

Laser light scattering techniques are used to examine the existence of a tubulin-ring or tubulin-aggregate equilibrium. Three principal components in addition to tubulin dimer have been observed. One large component having D20,w = 0.65 +/- 0.25 X 10(-7) cm2/s is in equilibrium with tubulin (dimer) at 4 degrees C. A second large component having D20,w = 0.74 +/- 0.05 X 10(-7) cm2/s is metastable at 4 degrees C and is formed when tubulin solutions are warmed to 36 degrees C and cooled back to 4 degrees C. The properties of the component reported in the previous paper (Gethner, J.S., Flynn, G.W., Berne, B.J., and Gaskin, F. (1977), Biochemistry 16 (preceding paper in this issue)) to sediment at 10 S to 20 S are shown to be consistent with a small, metastable aggregate of tubulin.