Physicochemical Characterization of Taurine Binding with Synaptic Membranes in the Chicken Brain

Abstract

Specific [³⁵S] taurine binding was studied using synaptic membranes prepared from chicken brain. Electron microscopy showed the membranes to be free of intracellular structures, but they nevertheless formed sealed membrane pouches. They bound taurine specifically with a binding constant of 67 μM, which apparently shows some dissociation of bound taurine inside the membrane pouches. Binding required Na⁺, K⁺, Ca²⁺ and Mg²⁺ions and had a pH optimum of pH 7 and a temperature optimum of 310°K. The activation energy of binding was 12.15 kJ/mol, calculated from the temperature course, and its free energy 21 kJ/mol, calculated from the equilibrium constant between the bound and free taurine. The number of specific binding sites was very low, only 37 pmol/g protein, while that of total binding sites was 1.1 nmol/g.