Stability of microtubule protein over the pH ranges 6.9–9.5

Abstract

The pH stability range of a microtubule protein preparation [porcine brain tissue] was investigated between 6.9 and 9.5. Microtubule protein was exposed to various pH values in this range and then returned to pH 6.0. The appearance of microtubules as verified by EM and sedimentation analysis under polymerizing conditions was taken as an indication of a conformationally stable protein. Between pH 6.9 and pH 8.0 the loss in the ability to form microtubules was reversible, at pH 8.2 it was partially reversible and above pH 8.2 it was irreversible. Tubulin and the microtubule-associated protein fraction were separately exposed to high pH. Tubulin exposed to high pH can still form microtubules in the presence of untreated microtubule-associated protein. Microtubule-associated protein exposed to high pH could not initiate microtubule assembly with untreated tubulin. Loss in ability of a microtubule protein preparation to assemble at high pH is due to a change in the microtubule-associated protein fraction and conformational stability of tubulin even after exposure to pH 9.5.