title: On the disposition of a phosphorylated protein ("synapsin I") and its associated kinases in synaptosomes from rat brain.
abstract: Endogenous phosphorylation of synapsin I (protein I), a phosphoprotein located on the surface of synaptic vesicles, was studied in vesicles prepared from synaptosomes lysed in the absence (control) or presence of 50 microM-cyclic AMP ("cAMP-treated"). Compared to synaptic plasma membrane (SPM) fractions prepared in parallel, and confirming previous work, the vesicle fractions were highly enriched on a unit protein basis in Ca2+-calmodulin-dependent kinase activity towards synapsin I. In contrast, with control vesicles the magnitude of the total phosphorylation of synapsin I in the presence of cyclic AMP was similar to that observed in SPM, but regulation by cyclic AMP was only partial. In "cAMP-treated" vesicles, however, synapsin I phosphorylation was highly enriched compared to SPM and the activity was virtually independent of cyclic AMP. The results show that while the free catalytic subunit of the cyclic AMP-dependent kinase remains associated with synapsin I during vesicle isolation the holoenzyme remains bound to membrane fragments, probably through its regulatory subunit.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin / Q000502:physiology; D000242:Cyclic AMP / Q000494:pharmacology; D066298:In Vitro Techniques; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D016704:Synapsins; D013574:Synaptosomes / Q000378:metabolism
chemical_list: D002147:Calmodulin; D009419:Nerve Tissue Proteins; D016704:Synapsins; D000242:Cyclic AMP; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases