Isolation, characterization, and purification to homogeneity of a rat brain protein (GABA-modulin).
gamma-Aminobutyric acid (GABA)-modulin is a brain neuropeptide that appears to modulate specific high-affinity (20 nM) GABA recognition sites in brain. When added to crude synaptic membranes this peptide inhibits binding of [3H]GABA to the high-affinity site and prevents facilitation of [3H]diazepam binding elicited by GABA. GABA-modulin has been purified to homogeneity by ammonium sulfate precipitation, gel chromatography, and reverse-phase HPLC. Homogeneity was confirmed by a variety of means, including chromatography under four different HPLC conditions, two different polyacrylamide gel electrophoreses, and end group analysis. Purified GABA-modulin contains approximately 126 amino acids and has a molecular weight of 16,500. The GABA-modulin molecule contains an abundance of hydrophilic basic residues, and neither cysteine nor GABA is present. End group analyses of GABA-modulin showed that histidine is the free COOH terminus and the NH2 terminus is blocked. GABA-modulin specifically blocked both [3H]GABA binding to synaptic membranes (IC50, 0.5 microM) and GABA-stimulated [3H]diazepam binding; the binding of [3H]GABA to low-affinity sites was not affected.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001923:Brain Chemistry; D002352:Carrier Proteins / Q000302:isolation & purification*; D002540:Cerebral Cortex / Q000378:metabolism; D050485:GABA Plasma Membrane Transport Proteins; D008297:Male; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000302:isolation & purification* / Q000378:metabolism; D027361:Organic Anion Transporters; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D027361:Organic Anion Transporters; D005680:gamma-Aminobutyric Acid