Aminoacylase 1 is a cytosolic, homodimeric, zinc binding enzyme that catalyzes the hydrolysis of acylated L amino acids to L amino acids and acyl group, and has been postulated to function in the catabolism and salvage of acylated amino acids. ACY1 has been assigned to chromosome 3p21.1, a region reduced to homozygosity in small cell lung cancer (SCLC), and its expression has been reported to be reduced or undetectable in SCLC cell lines and tumors. The amino acid sequence of human aminoacylase 1 is highly homologous to the porcine counterpart, and ACY1 is the first member of a new family of zinc binding enzymes.