Study of the specificity of amino acid binding protein fromSaccharomyces cerevisiae membranes

Membranes obtained from exponentially growing yeast were extracted with buffered solution of 1% Tween 80 plus 0.1m MgCl₂. The soluble proteins, saparated from detergent and fine membrane particles on Saphadex G-100 colunn, were fond, to have binding affinity for Val, Lau, Ileu, Asp, Lys, His, Arg, Phe and Met. The occurrence of individual binding activities in different preparations was irregular. This and the fast inactivation by aging showed the extrame sensitivity of the molecules of binding proteins towards deleterious agents. Saturation of the binding proteins with aspartic acid and phenylalanine was of an identical biphasic shape indicating the change ofK _diss and suggesting the existence of several binding sites for each amino acid. In our opinion the above listed observations imply low specificity of amino acid binding proteins in yeast.