Comparison of a 52‐kDa Phosphoprotein from Synaptic Plasma Membranes Related to Long‐Term Potentiation and the Major Coated Vesicle Phosphoprotein

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Abstract
In the in vitro hippocampal slice preparation a short tetanus induces long‐term potentiation (LTP) and an increase in the post hoc phosphorylation of a 52‐kDa protein in synaptosomal plasma membranes (SPM) prepared from these slices. This 52‐kDa SPM phosphoprotein closely resembles the predominant phosphoprotein in coated vesicles, pp50, with respect to the insensitivity of its phosphorylation to Ca2+/calmodulin and cyclic AMP. This resemblance prompted us to compare in rat brain the 52‐kDa SPM protein with pp50 in isolated coated vesicles. Both proteins appear to be very similar on basis of the following criteria: (1) relative molecular weight on sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, (2) peptide mapping, (3) phospho‐amino acid content, and (4) isoelectric point. Since coated vesicles are thought to be involved in receptor‐mediated endocytosis and membrane recycling, our data suggest that LTP‐correlated changes in 52‐kDa phosphorylation may reflect increased coated vesicle activity.