Gurmarin is a 35-residue polypeptide from the Asclepiad vine Gymnema sylvestre (Gurmar). It has been utilised as a pharmacological tool in the study of sweet-taste transduction because of its ability to selectively inhibit the neural response to sweet tastants in rats.
As a sweet-taste-suppressing protein, gurmarin is only active on rodent sweet taste receptors but not on that of humans. ref: Appl Microbiol Biotechnol. 2012 Nov;96(3):619-30