The phosphorylation of choline acetyltransferase.
Human placental Choline Acetyltransferase (ChAT) has been shown to be phosphorylated in vitro by kinases present in rat brain. Phosphorylation occurs at a single site with the exclusive phosphoamino acid being serine. ChAT phosphorylation was shown to be calcium, and not cyclic nucleotide, dependent and was inhibited by inhibitors of calcium/calmodulin protein kinases including anti-calmodulin anti-sera. ChAT phosphorylation was stimulated by calmodulin (9 fold) and, to a lesser extent, by phosphatidylserine (4 fold). These results indicate the involvement of a calcium/calmodulin and possibly also a calcium/phospholipid kinase. This finding was confirmed by demonstrating ChAT phosphorylation using both purified multifunctional calcium/calmodulin protein kinase (CaMK) and calcium/phospholipid protein kinase C (PKC) from rat brain. A stoichiometric incorporation of 0.9 mol phosphate/mol ChAT was achieved by CaMK. Phosphorylated ChAT could be isolated from freshly prepared rat brain synaptosomes. The results obtained with this model system support the hypothesis that in vivo a fraction of ChAT exists phosphorylated.
Bruce
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Department of Biochemistry, University of Texas, Dallas 75235.
Hersh
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LB
D000596:Amino Acids / Q000032:analysis / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D002795:Choline O-Acetyltransferase / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D010920:Placenta / Q000201:enzymology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000201:enzymology; D013574:Synaptosomes / Q000201:enzymology
D000596:Amino Acids; D002147:Calmodulin; D010446:Peptide Fragments; D010710:Phosphates; D047428:Protein Kinase Inhibitors; D004533:Egtazic Acid; D002795:Choline O-Acetyltransferase; D011494:Protein Kinases; D002118:Calcium