L-Pipecolic acid accumulates in the generalized peroxisomal disorders such as Zellweger syndrome and neonatal-onset adrenoleukodystropy, as well as in several other groups of patients with progressive neurologic diseases. While a defect in L-pipecolic acid oxidation is recognized in the majority of children with generalized peroxisomal disorders, the cause of this defect is unknown. Because of the apparent neurologic role of L-pipecolic acid and its metabolites, this elevation of L-pipecolic acid may be related to the profound mental retardation found in these diseases. The catabolic enzyme for L-pipecolic acid oxidation has recently been purified to near homogeneity and a polyclonal antibody to the enzyme has been produced. This project will focus on further studies with this purified enzyme. Major foci will include a study of the distribution and relative activity of the enzyme in brain tissues, further study of the covalent flavin- containing portion of the protein, cloning of the enzyme and determination of its genetic characteristics, and identification of and studies of patients with defects in the enzyme. This work will yield information on the normal L-pipecolic acid oxidation pathway and will also help elucidate the etiology of the L-pipecolic acid oxidation defects in peroxisomal diseases, as well as in those rarer patients with other forms of hyperpipecolic acidemia. Further studies with the protein will allow us to identify whether the enzyme contains the typical carboxyl terminal amino acid sequences involved in the targeting of enzymes to the peroxisomes. With both the antibody and the partial amino acid sequence information, it should be possible to produce cDNA clones for the enzyme. These clones will be tools for future studies to characterize hyperpipecolic acidemia at the genetic level and to find a genomic clone, so that common characteristics such as upstream segments that regulate and synchronize peroxisomal enzyme production may be distinguished. In addition, the identification of patients with a point defect of L-pipecolic acid oxidation would be particularly enlightening because any metabolic and neurologic changes found in such patients can only be attributed to this defect.
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