Calcium-sensitivity of the microtubule reassembly system. Difference between crude brain extract and purified microtubular proteins.

Microtubule reassembly in crude extracts of porcine brain was inhibited by 10(-5) M Ca2+, wherease 10(-3) M Ca2+ was required for inhibition of the reassembly from purified microtubular proteins. This accounts for the apparent discrepancies between the results reported by other investigators. Furthermore, the Ca-sensitivity of the purified microtubular proteins was nearly completely recovered on addition of a fraction obtained from crude brain extract.