Abstract
1. The effects of specific protein modifying reagents on the dose (Glu)-response (ΔG) relationship of the glutamate-hyperpolarizing (Glu-H) receptors in molluscan neurons (Onchidium verruculatum) were analyzed. 2. The effects could be classified into three types. (1) Type I, parallel shift of the dose-response curve towards higher concentration by modification of COO- groups by N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ). The double reciprocal plots of the dose-response curves before and after the treatment indicated competitive inhibition type modification. (2) Type II, a decrease in the slope of the dose-response curve through modification of -SH by N ethylmaleimide and -NH3 groups by trinitrobenzenesulfonic acid. The double reciprocal plots indicated non-competitive inhibition type modification. (3) The combined effects of Type I and Type II, after modification of arginyl residues with diacetyl trimer. The modification was most effective when applied during an activated state of receptors and channels by Glu. 3. EEDQ had an irreversible after-effect on Glu-H type Onchidium neurons to activate an additional Na+ permeability increase in Glu induced hyperpolarizing response. 4. Pretreatment of N acetylimidazole (NAI), Glu-H (including weak D) receptors in Helix aspersa produced no significant difference in Glu response. However, simultaneous application of NAT and Glu induced an additional Na+ permeability increase, probably by modification of tyrosyl residues. This indicates the greatest effectiveness of the NAI modification during the activated state of the receptors and the channels by Glu. 5. It is suggested that the Glu-H receptor protein possesses both negatively and positively charged residues, containing COO- and arginyl+ in the receptive site, and that several amino acid resides (-SH, -NH, arginyl, and tyrosyl) act in the Glu-activated receptors and channels as their subsites. 6. The role of the subsites in the receptors and channels is discussed.
