Sphingosine-1-phosphate lyase catalyzes the last step in sphingolipid breakdown, the cleavage of phosphorylated sphingoid bases such as sphingenine-1-phosphate. The latter lipid is not only a catabolite, but can influence as an inter- and/or intracellular second messenger many cellular processes. To allow for the diagnosis of human disorders that might be linked to a deficient lyase, the human sphingosine-1-phosphate lyase cDNA was cloned. The obtained cDNA encoded a protein of 568 amino acids with a calculated molecular mass of 63 492 Da. Hydropathy plots revealed the presence of one membrane span near the amino-terminal which is however not required for enzyme activity since recombinant poly-His-tagged lyase, lacking this membrane span, was functionally active. Site-directed mutagenesis disclosed the importance of the cysteine residues 218 and 317 for the cleavage reaction. Northern analysis showed the presence of rare large-sized mRNAs of 6.7, 5.8 and 4 kb and the highest expression in liver. By fluorescent in situ hybridization, the gene was mapped to chromosome 10q22.