Ligand Recognition of Taste Receptors

We tested the prediction that enantiomeric pairs of compounds of which one partner elicits sweetness and the other partner bitterness should not be recognized by structurally unrelated taste receptors with independent evolutionary origins. They rather have been proposed to be recognized by structurally related pairs of receptors. To this end we focused on the Dand L-forms of tryptophan and phenylalanine. We used in vitro assays to examine receptor responsiveness to the test substances and genetically engineered mice to test implications of taste quality coding. Our data are inconsistent with the prediction. They indicate that D- and L-forms of tryptophan and phenylalanine are recognized by the unrelated sweet and bitter taste receptors, respectively.