Sedimentation velocity analyses of the effect of hydrostatic pressure on the 30 S microtubule protein oligomer.

Increasing hydrostatic pressure in the analytical ultracentrifuge by increasing rotor velocity and overlayering protein samples with oil caused a depolymerization of the 30 S oligomer of microtubule protein. This results indicates that the reaction of 6 S microtubule protein to form the oligomer was accompanied by a positive volume change. The effect of hydrostatic pressure on the 6 S to 30 S transition was employed to demonstrate the presence of a rapidly reversible equilibrium between these components by showing polymerization or depolymerization of the oligomer during the course of ultracentrifugation. The magnitude of the partial specific volume change accompanying this reaction was estimated from mass fraction measurements of microtubule protein solutions at a variety of hydrostatic pressures to be about 9 X 10(-4) ml g-1.