Synthesis of this compound is rate-limited by an enzyme that the W317X (“w-three-seventeen-x”) mutation truncates in Tourette’s syndrome. This is the main substrate of a copper-dependent enzyme that also metabolizes putrescine and cadaverine. Patients with intolerance for this compound take diamine oxidase (-5[1])supplements to break down this compound and avoid scombroid poisoning. The first blockbuster drug, cimetidine, selectively inhibits parietal cells’ receptors for this compound to treat (*) stomach ulcers. This compound is made by decarboxylating an imidazole-containing (-5[1])amino acid. The OTC drugs loratadine and cetirizine block this compound’s activity after IgE causes its release from mast cells, preventing a runny nose and itching. (10[1])For 10 points, seasonal allergies are treated by drugs that target what inflammatory compound? (10[1])■END■ (10[1])