What confers specificity on glycine for its receptor site?

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Abstract
1 The structural requirements for activation of the glycine receptor were studied in isolated ventromedial hypothalamic neurones of rats by use of a ‘concentration-clamp’ technique under single-electrode voltage-clamp conditions. 2 α-Amino acids (l-α-alanine, and d-α-alanine, and l-serine), and glycine-methylester, glycine-ethylester and β-amino acids (β-alanine and taurine) produced a transient inward Cl− current, which was similar to that induced by glycine. 3 The responses to individual α- and β-amino acids were selectively antagonized by strychnine, but were not affected by bicuculline, picrotoxin or the taurine antagonist, TAG (6-aminomethyl-3-methyl-4H,1,2,4-benzothiadiazine-1,1-dioxide hydrochloride), suggesting that α- and β-amino acids activate the same glycine receptor. 4 β-Amino acids were slightly more potent than the α-amino acids in causing cross-desensitization of the glycine response. 5 From the results of the structure-activity analysis of the optical isomers of α-alanine, serine and cysteine, a tentative structure of the glycine receptor is proposed.