Abstract
Publisher Summary This chapter describes procedures for the isolation of the subunits of phosphatase and reconstitution of the holoenzyme. Calmodulin-dependent protein phosphatase, also referred to as modulator-binding protein, CaM-BP 80 , and calcineurin, is a heterodimer consisting of subunit A (M r 60,000) and subunit B (M r 19,000). Subunit A holds the catalytic and calmodulin-binding sites whereas subunit B, which has no phosphatase activity and 35% sequence homology with calmodulin, binds four Ca 2+ ions with high affinity. The enzyme has broad substrate specificity, removing phosphate groups from both protein (phosphorylated on serine, threonine, or tyrosine residues) and nonprotein (such as p-nitrophenylphosphate) substrates. Phosphatase activity is reported to be stimulated by Ca 2+ , Co 2+ , Mg 2+ , Mn 2+ , Ni 2+ , and Zn 2+ . Because of its localization at postsynaptic densities, and the microtubules of postsynaptic dendrites and its synthesis during synaptogenesis, the enzyme plays an important role in certain synaptic functions. Calmodulin-dependent protein phosphatase is purified to apparent homogeneity from bovine brain.
Published Version
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