L-[3H]lysine binding to rat retinal membrane: I. Quantitative determination and characterization of the binding sites

A saturable reversible binding to membranes from rat retina has been found for L-[3H]lysine. Specific binding is time, temperature and protein concentration-dependent, and shows stereospecificity. The best computer fits of the experimental data are obtained with a receptor model based on two independent binding sites, of which only one site with a Kd value of 229.4 +/- 14.23 nM and a Bmax of 2.04 +/- 0.11 pmol/mg protein could be characterized satisfactorily. Several compounds included putative neurotransmitters have moderate or no affinity for L-lysine binding sites. A different pattern of distribution of L-[3H]lysine binding sites is observed among various regions of the brain, with the highest density in the occipital cortex, and the lowest density in ponsmedulla. The existence of binding sites in rat retinal membranes for L-lysine, as well as in the areas involved in the visual pathway, suggests a role for this amino acid in the physiological mechanism of the visual function.