The Journal of biological chemistry
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Comparative Study
Localization of the cAMP-dependent protein kinase to the postsynaptic densities by A-kinase anchoring proteins. Characterization of AKAP 79.
Postsynaptic densities (PSD) are a network of proteins located on the internal surface of excitatory synapses just inside the postsynaptic membrane. Enzymes associated with the PSD are optimally positioned to respond to signals transduced across the postsynaptic membrane resulting from excitatory synaptic transmission or neurotransmitter release. We present evidence suggesting that type II cAMP-dependent protein kinase (PKA) is anchored to the PSD through interaction of its regulatory subunit (RII) with an A-Kinase Anchor Protein (AKAPs). ⋯ Co-localization of the type II PKA in purified PSD fractions was confirmed immunologically by detection of RII and enzymologically by measuring cAMP-stimulated phosphorylation of the heptapeptide substrate Kemptide. Approximately 30% of the PSD kinase activity was specifically inhibited by PKI 5-24 peptide, a highly specific inhibitor of PKA. We propose that AKAP 79 and AKAP 150 function to anchor the type II PKA to the PSD, presumably for a role in the regulation of postsynaptic events.
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Myosin light chain phosphatase associated with smooth muscle myosin (MAPP) was isolated from chicken gizzard. The MAPP was tightly associated with myosin and was not dissociated from myosin under the physiological ionic conditions. The phosphatase was dissociated from myosin in the presence of high MgCl2, i.e. 80 mM MgCl2. ⋯ The properties of the myosin-associated phosphatase were distinct from the phosphatases reported previously, although some properties were similar to smooth muscle phosphatase-IV. Therefore, it is concluded that MAPP I is a novel smooth muscle protein phosphatase. Since it strongly associated with smooth muscle myosin, it is likely that MAPP I is responsible for the dephosphorylation of smooth muscle myosin in situ.