A sulfur-containing amino acid of Felis catus and some other members of the Felidae, excreted in the urine of cats and is particularly concentrated in intact male cats; has cysteine and methionine precursors; is 2-amino-7-hydroxy-5,5-dimethyl-4-thiaheptanoic acid; in blood is a bound glutathiuone conjugate peptide; gamma glutamy felinyl glycine; likely serves as a precursor to a territorial pheromone marker.