title: Phosphorylation induces a decrease in the biological activity of the protein inhibitor (GABA-modulin) of gamma-aminobutyric acid binding sites.
abstract: gamma-Aminobutyric acid (GABA)-modulin is a brain protein of Mr 16,500 that down-regulates the high-affinity binding site for GABA which is located in crude synaptic membranes. This protein can be phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase and by a partially purified preparation of calmodulin-sensitive Ca2+-dependent protein kinase. The GABA-modulin sites that are phosphorylated by the two enzymes are different, as revealed by HPLC analysis of tryptic digests. The capacity of GABA-modulin to decrease the number of sites that bind [3H]muscimol was completely abolished by phosphorylation of this protein with the cAMP-dependent protein kinase but not with the Ca2+-dependent enzyme. GABA-modulin present in crude synaptic membranes prepared from rat cortex also was shown to be phosphorylated by endogenous protein kinases activated by cAMP, Ca2+ and calmodulin, and Ca2+ and phosphatidylserine. These results suggest a potentially important role for protein kinase and GABA-modulin in the regulation of the number of GABA recognition sites.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D027361:Organic Anion Transporters; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011963:Receptors, GABA-A; D013570:Synaptic Membranes / Q000378:metabolism
chemical_list: D002147:Calmodulin; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D027361:Organic Anion Transporters; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D011494:Protein Kinases; D002118:Calcium