Putative taste receptor. TAS1R1/TAS1R3 responds to the umami taste stimulus (the taste of monosodium glutamate) and also to most of the 20 standard L-amino acids, but not to their D-enantiomers or other compounds. Sequence differences within and between species can significantly influence the selectivity and specificity of taste responses. Forms heterodimers with TAS1R3. Expressed strongly only in fungiform papillae. Belongs to the G-protein coupled receptor 3 family. TAS1R subfamily.