The invention relates to compounds that specifically bind a T1R1/T1R3 or T1R2/T1R3 receptor or fragments or sub-units thereof. The present invention also relates to the use of hetero-oligomeric and chimeric taste receptors comprising T1R1/T1R3 and T1R2/T1R3 in assays to identify compounds that respectively respond to umami taste stimuli and sweet taste stimuli. Further, the invention relates to constitutive cell lines that stably or transiently co-express a combination of T1R1 and T1R3; or T1R2 and T1R3 subunit polypeptides; wherein the T1R1, T1R2 or T1R3 subunit polypeptides are chimeric polypeptides and/or comprise T1R subunits of different species and are expressed in these cell lines under constitutive or inducible conditions. The use of these cells lines in cell-based assays to identify umami and sweet taste modulatory compounds is also provided, particularly high throughput screening assays that detect receptor activity by use of fluorometric imaging.