Fibrillar proteins from squid axons: II. Microtubule protein

From the axoplasm of the Chilean squid Dosidicus gigas the protein tubulin that binds colchicine has been isolated, analyzed and studied physically. The property of binding colchicine was found to be very labile and the isolation of tubulin was effected best from rapidly lyophilized axoplasm. The protein is acidic, and has a molecular weight of 60,000. Conditions for the preservation of intact microtubules in a dispersion of axoplasm were found and a comparison was made with these conditions and those for optimum colchicine binding to attempt to confirm the identity of tubulin with the subunit of the microtubule