The saturable binding of [3H]strychnine to synaptic membrane fractions of rat spinal cord appears to involve an interaction with synaptic receptor sites for the neurotransmitter actions of glycine. Binding exhibits a dissociation constant for strychnine of 2.6 to 4 nM and an EC50 for glycine inhibition of strychnine binding of 25 μM. Association kinetics is bimolecular, with a rate constant of 1.0 x 107 M-1 sec-1, while dissociation of the strychnine receptor complex is first order, with a rate constant of 1.54 x 10-2 sec-1. The dissociation constant (k2/k1) of 1.54 nM is similar to that obtained from equilibrium data. Monovalent cations increase specific and decrease nonspecific strychnine binding, while divalent cations are without effect. Surfactants such as deoxycholate and Triton X100 decrease receptor binding in concentrations which solubilize membrane protein. Displacement curves of [3H]strychnine by glycine indicate cooperative interactions with a Hill coefficient of 1.7, whereas the Hill coefficient for displacement of [3H]strychnine by unlabeled strychnine is 1.0. Diazonium tetrazole and acetic anhydride preferentially inhibit displacement of [3H]strychnine binding by glycine and reduce the Hill coefficient of glycine displacement curves. Guanidine, N ethylmaleimide, and increases in pH also lower the Hill coefficient for glycine displacement. Diazonium tetrazole slows the dissociation of [3H]strychnine elicited by excess glycine without altering dissociation produced by excess unlabeled strychnine. Glycine and strychnine appear to bind to distinct sites which interact in a cooperative fashion.
|Original language||English (US)|
|Number of pages||20|
|State||Published - Jan 1 1974|
ASJC Scopus subject areas
- Molecular Medicine