Abstract A crude extract of yeast was chromatographed on a column of Sepharose containing covalently bound L-tyrosine. The tyrosine-sensitive 3-deoxy-D- arabino -heptulosonate-7-phosphate (DAHP) synthetase was retarded by the column relative to the bulk of the protein and was purified about 100-fold. In contrast, the phenylalanine-sensitive enzyme was not retarded. No retardation was found on an unsubstituted Sepharose column. The purification presumably resulted from the specific interaction between the effector-binding site of the enzyme and the effector attached to Sepharose.