Membrane phosphoproteins of rat hippocampus: sensitivity to tetanic stimulation and enkephalin.
Hippocampal slices are electrically stimulated in the perforant path with a pulse-train, which can lead to long-term potentiation (LTP). Of the thus stimulated slices, subcellular fractions are prepared and used in an endogenous protein phosphorylation assay. A phosphoprotein band which was reported earlier to be sensitive to electric stimulation as well as to methionine-enkephalin is now further analyzed: it consists of two phosphoproteins only slightly differing in molecular weight: 50,000 Mr (50 K) and 52,000 Mr (52 K), but having distinct biochemical properties and subcellular localization. Their IEP is dissimilar (3.5-4.3 and 5.3, respectively), they display different sensitivity towards calcium when tested in the phosphorylation assay, but are both cAMP-independently phosphorylated. Only one of them responds to tetanic stimulation with an increased phosphorylation post hoc. This protein, the 52 K component, is localized in synaptic membranes. Moreover, this protein also responds to incubation of slices with methionine-enkephalin. The phosphorylation of the 50 K component is not influenced by electric stimulation, nor by incubations with neuropeptides; its phosphorylation takes place in material sedimenting with the mitochondrial cell fractions and is strongly calcium- and calmodulin-dependent.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D006624:Hippocampus / Q000032:analysis / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000302:isolation & purification*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
D002147:Calmodulin; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D004744:Enkephalin, Methionine; D000242:Cyclic AMP; D002118:Calcium