L-Cysteinesulfinic acid is an excitatory amino acid and agonist of metabotropic glutamate receptors (mGluRs).1,2 It increases intracellular inositol phosphate levels in CHO cells expressing mGluR1, mGluR5, or mGluR8 (EC50s = 120, 30, and 110 μM, respectively) and inhibits forskolin-induced cAMP production in CHO cells expressing mGluR2 or mGluR6 and hamster kidney cells expressing mGluR4 (EC50s = 100, 100, and 2,000 μM, respectively).2 It selectively binds to mGluR1α (Ki = 3,510 nM) over adrenergic, dopamine, histamine, muscarinic, nicotinic, or serotonin receptors (Kis = >10,000 nM for all). L-Cysteinesulfinic acid (1 mM) decreases mean arterial blood pressure and heart rate in rats when microinjected into the nucleus tractus solitarius (NTS).1 L-Cysteinesulfinic acid can be formed via oxidation of L-cysteine by reactive oxygen species (ROS), and conversion of cysteine to L-cysteinesulfinic acid in cysteine-containing peptide probes has been used to measure oxidative stress.3

|1. Takemoto, Y. Cardiovascular actions of L-cysteine and L-cysteine sulfinic acid in the nucleus tractus solitarius of the rat. Amino Acids 46(7), 1707-1713 (2014).|2. Shi, Q., Savage, J.E., Hufeisen, S.J., et al. L-homocysteine sulfinic acid and other acidic homocysteine derivatives are potent and selective metabotropic glutamate receptor agonists. J. Pharmacol. Exp. Ther. 305(1), 131-142 (2003).|3. Keng, C.-L., Lin, Y.-C., Tseng, W.-L., et al. Design of peptide-based probes for the microscale detection of reactive oxygen species. Anal. Chem. 89(20), 10883-10888 (2017).