L-pipecolic acid oxidase, a human enzyme essential for the degradation of L-pipecolic acid, is most similar to the monomeric sarcosine oxidases

L-Pipecolic acid oxidase activity is deficient in patients with peroxisome biogenesis disorders (PBDs). Because its role, if any, in these disorders i s unknown, we cloned the associated human gene and expressed its protein pr oduct. The cDNA was cloned with the use of a reverse genetics approach base d on the amino acid sequence obtained from purified L-pipecolic acid oxidas e from monkey. The complete cDNA, obtained by conventional library screenin g and 5' rapid amplification of cDNA ends, encompassed an open reading fram e of 1170 bases, translating to a 390-residue protein. The translated prote in terminated with the sequence AHL, a peroxisomal targeting signal 1. Indi rect immunofluorescence studies showed that the protein product was express ed in human fibroblasts in a punctate pattern that co-localized with the pe roxisomal enzyme catalase. A BLAST search with the amino acid sequence show ed 31% identity and 53% similarity with Bacillus sp. NS-129 monomeric sarco sine oxidase, as well as similarity to all sarcosine oxidases and dehydroge nases, No similarity was found to the peroxisomal D-amino acid oxidases. Th e recombinant enzyme oxidized both L-pipecolic acid and sarcosine. However, PBD patients who lack the enzyme activity accumulate only L-pipecolic acid , suggesting that in humans in vivo, this enzyme is involved mainly in the degradation of L-pipecolic acid.