[Cooperative binding of calcium ions by photoreceptor membranes]

Equilibrium calcium binding by photoreceptor membranes of cattle retina in 5 mM tris-HCl buffer, pH = 7.4 at 5 degrees C in concentration interval from 2 X 10(-7) M to 2 X 10(-3) M has been studied. Binding of Ca2+ was found to depend on the manner of photoreceptor membranes preparation. Cooperative effect of Ca2+ binding in concentration interval from 2 X 10(-7) M to 10(-5) M was observed.