What activates gustatory receptors for umami taste?

• A. The amino acid L-glutamate.
• B. The carbohydrate glucose.
• C. The amino acid L-arginine.
• D. The fatty acid palmitate.

Answer: (A)

Umami is the savory taste produced by certain amino acids, with free L-glutamate being the primary activator. When glutamate is present, it binds to gustatory receptors on taste cells—most notably the T1R1/T1R3 receptor complex—triggering a signaling cascade that depolarizes the cell and releases neurotransmitters to activate the gustatory nerve fibers. Monosodium glutamate is a well-known umami stimulus because it provides glutamate readily. The other options are linked to other tastes: glucose evokes sweet taste via different receptors, arginine doesn’t strongly activate umami receptors, and palmitate relates to fat taste rather than umami.