Abstract
Acid and alkaline phosphatase activity, determined by the hydrolysis of p‐nitrophenyl phosphate, was found in preparation 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 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.