Calmodulin-stimulated phosphorylation of 17 beta-estradiol receptor on tyrosine (original) (raw)

The calf uterine 17P-estradiol receptor is a phosphoprotein. Phosphorylation-dephosphorylation of the receptor is controlled by a cytosol receptor kinase that activates the hormone binding and by a nuclear phosphatase that inactivates this binding. This report concerns the nature of the 1713-estradiol receptor kinase. Highly purified calf uterus 17/3estradiol receptor preinactivated by the nuclear phosphatase was used as substrate of the purified receptor kinase. Ca2" and calmodulin stimulate both the kinase-dependent activation of the hormone binding and 32p incorporation from [v-32p]1 ATP into the receptor. Maximal stimulation of hormone binding activation requires 1 ,AM Ca2' and 0.6 ,uM calmodulin.