INTERACTIONS BETWEEN CALCIUM-DEPENDENT REGULATOR PROTEIN OF CYCLIC NUCLEOTIDE PHOSPHODIESTERASE AND MICROTUBULE PROTEIN .2. ASSOCIATION OF CALCIUM-DEPENDENT REGULATOR PROTEIN WITH TUBULIN DIMER

Abstract

The porcine brain Ca2+-dependent regulator protein (CDR) of cyclic nucleotide phosphodiesterase (PDE) was reported to be a Ca2+-dependent regulator of microtubule (MT) assembly. The binding of Ca2+-CDR complex to tubulin dimer was investigated to elucidate the Ca2+-dependent inhibitory action of CDR on MT assembly. Purified microtubular proteins (PMP) isolated from porcine brain did not affect the ability of CDR to activate Ca2+-activatable PDE, and did not include any inhibitory protein of Ca2+-activatable PDE. The binding of CDR to the tubulin dimer was observed on Sephadex G-200 gel filtration and ammonium sulfate fractionation in a Ca2+-dependent manner. CDR did not bind to microtubule associated proteins. Ca2+-dependent inhibition of MT assembly by CDR is apparently due to the binding of CDR to tubulin dimer in a Ca2+-dependent manner.