Characterization of acid and alkaline phosphatase activity in preparations of tubulin and microtubule-associated proteins.

Acid and alkaline phosphatase activity, determined by the hydrolysis of p-nitrophenyl phosphate, was found in preparations of microtubules purified from bovine brain by temperature-dependent assembly-disassembly and ion-exchange chromatography. Phosphocellulose-purified tubulin contained an associated acid phosphatase activity, stimulated by Mg2+ and by Zn2+. Alkaline phosphatase activity with a pH optimum of 10.4 was measured in a fraction of microtubule-associated proteins (MAPs). Kinetics and the effects of sodium fluoride, sodium tartrate, sulfhydryl-blocking agents, EDTA and Zn2+ are reported.