Biological properties of a calcium-modulator protein from Phycomyces blakesleeanus

1. A modulator protein having properties similar to calmodulin-like proteins could be detected in Phycomyces the first day of growth. 2. The modulator protein from Phycomyces was partially purified to a specific activity of 9,000 Units/mg protein. 3. The modulator protein was similar to calmodulin with respect to: (a) the ability to stimulate a calcium-plus-calmodulin-dependent cAMP phosphodiesterase from bovine brain; (b) the inhibitory effect of trifluoperazine in this process; (c) the stimulation of the [Ca2+ + Mg2+)-ATPase from human erythrocyte membranes. 4. Maximum effect of modulator protein in the above mentioned reactions was achieved at micromolar calcium concentrations.