Microtubule Assembly in the Presence of Adenosine Triphosphate

Abstract

Microtubule (MT) assembly was investigated in the presence of ATP and Ca ions using both crude extract (CE) and purified microtubular proteins (PMP) prepared from porcine brains. ATP inhibited MT assembly from CE prepared with the reassembly buffer containing 1mM GTP. Half-maximal inhibition occurred at an ATP concentration of 0.4-0.5mM. Calcium ions, on the contrary, cancelled the ATP-induced inhibition, 1-2 μm calcium ions supporting maximal MT assembly. The ATP-induced inhibition in PMP was not so prominent as in CE, but occurred significantly in the presence of RNA. In PMP dissolved in the reassembly buffer containing ATP and yeast tRNA, the content of the ring fraction decreased significantly as compared with PMP containing only RNA. Furthermore, microtubule-associated proteins were found to be capable of binding ATP. The significance of the ATP-induced inhibition of MT assembly and the release of the inhibition by Ca²⁺ was discussed.