ISOLATION OF HYDROPHOBIC PROTEINS BINDING NEUROTRANSMITTER AMINO ACIDS: γ‐AMINOBUTYRIC ACID RECEPTOR OF THE SHRIMP MUSCLE

The total lipid extract of shrimp muscle ( Artemisia longinaris ) was precipitated with ether. The supernatant containing 95 per cent of the phospholipids and 50 per cent of the protein showed binding for L‐[ 14 C]glutamatc in the first peak of protein. The sediment, redissolved in chloroform‐methanol was chromatographed on a Sephadex LH‐20 column. A single peak was eluted in the chloroform (20‐40 ml) having no lipid phosphorous and high affinity binding for [ 14 C]GABA. The saturation was achieved at 1 mole per 80.000 g protein and the curve revealed a single type of binding site. The purification achieved was of about 4000‐fold. There was no binding of L‐[ 14 C]glulamate to the ether precipitate. The specificity of the binding of [ 14 C]GABA was further supported by competition experiments with bicuculline. picro‐toxin and muscimol. It is suggested that the hydrophobic protein isolated by us represents the GABA receptor. The findings presented in the two papers of the series suggest that the excitatory and inhibitory receptor from crustacean muscle can be separated as two different proteins.