The functional significance of calmodulin binding to human erythrocyte spectrin has been investigated under native conditions. Both native calmodulin and calmodulin derivatized with the photoactivable cross-linker methyl 4-azidobenzimidate (azidocalmodulin) have been used. When azidocalmodulin is photolyzed in the presence of erythrocyte ghosts, ghost extracts, or purified protein, it cross-lin...

Previous work has shown that 1,25-dihydroxy-vitamin D3 rapidly increases calmodulin levels of skeletal muscle membranes without altering the muscle cell calmodulin content. Therefore, the effects of the sterol on the binding of calmodulin to specific muscle membrane proteins were investigated. Soleus muscles from vitamin D-deficient chicks were treated in vitro for short intervals (5-15 min) wi...

The levels of calmodulin and calmodulin-binding proteins have been determined in cultured skin fibroblasts from patients with cystic fibrosis (CF) and age- and sex-matched controls. Calmodulin ranged from 0.20 to 0.76 microgram/mg protein; there was no difference between calmodulin concentration in fibroblasts from CF patients and controls. Calmodulin-binding proteins of 230, 212, 204, 164, 139...

A calmodulin-dependent protein phosphatase has been identified in human platelets by its cross-reactivity with an antibody developed against a bovine brain calmodulin-dependent protein phosphatase and by its calmodulin-stimulated dephosphorylation of 32P-labeled substrates. The platelet enzyme was partially purified to separate it from calmodulin and calmodulin-independent phosphatases. The par...

A protein that resembles vertebrate calmodulins and troponin C has been isolated from Chlamydomonas flagella by using a calmodulin purification protocol that included calcium-dependent affinity-based adsorption chromatography on phenothiazine-Sepharose conjugates. The flagellar protein resembled calmodulin in elution from reverse-phase columns, had a peptide map similar to that of calmodulin, a...

In rat striatum, the activation of adenylate cyclase by the endogenous Ca2+-binding protein, calmodulin, is additive with that of GTP but is not additive with that of the nonhydrolyzable GTP analog, guanosine-5'-(beta, gamma-imido)triphosphate (GppNHp). One possible mechanism for this difference could be an effect of calmodulin on GTPase activity which has been demonstrated to "turn-off" adenyl...

Ca2+-regulated guanylate cyclase in ciliary membranes from Paramecium contained tightly bound calmodulin. Antisera against calmodulin from Tetrahymena and soybean inhibited enzyme activity. EGTA did not easily release calmodulin; however, La3+ inhibited guanylate cyclase by dissociation of calmodulin. While La could not replace Ca in the activation of guanylate cyclase, it substituted for Ca2+ ...

The concentration requirements of calmodulin in altering basal, GTP-, and dopamine-stimulated adenylate cyclase activities in an EGTA-washed particulate fraction from bovine striatum were examined. In the bovine striatal particulate fraction, calmodulin activated basal adenylate cyclase activity 3.5-fold, with an EC50 of 110 nM. Calmodulin also potentiated the activation of adenylate cyclase by...

Calmodulin stimulated the rate of Mg2+-induced polymerization of human platelet actin. The stimulatory effect was due to an increase in the nucleation phase of the reaction; there was no effect on the steady-state viscosity. The calmodulin antagonist trifluoperazine blocked the stimulatory effect of calmodulin. Addition of EGTA to the reaction mixture also stimulated the rate of actin polymeriz...

Small conductance Ca(2+)-activated potassium channels (SK channels) are coassembled complexes of pore-forming SK alpha subunits and calmodulin. We proposed a model for channel activation in which Ca2+ binding to calmodulin induces conformational rearrangements in calmodulin and the alpha subunits that result in channel gating. We now report fluorescence measurements that indicate conformational...