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  • Title: On the disposition of a phosphorylated protein ("synapsin I") and its associated kinases in synaptosomes from rat brain.
    Author: Rodnight R, Gower HJ, Robertson RG.
    Journal: Neurochem Res; 1984 Jun; 9(6):771-83. PubMed ID: 6092985.
    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.
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