title: 3-Hydroxy-3-methylglutaryl coenzyme A lyase: targeting and processing in peroxisomes and mitochondria.
abstract: 3-Hydroxy-3-methylglutaryl coenzyme A lyase (HL, E.C. 4.1.3.4) has a unique dual localization in both mitochondria and peroxisomes. Mitochondrial HL ( approximately 31.0 kDa) catalyzes the last step of ketogenesis; the function of peroxisomal HL ( approximately 33.5 kDa) is unknown. On density gradient fractionation, normal human lymphoblasts contain both peroxisomal and mitochondrial HL whereas in lymphoblasts from a patient with Zellweger syndrome, in which functional peroxisomes are absent, only the mitochondrial HL isoform was present. To study the kinetics of the dual targeting of HL, we performed pulse-chase experiments in normal and Zellweger cells. Pulse-chase studies revealed a biphasic curve for processing of the HL precursor. The first phase, with a calculated half-life of approximately 3 h in both normal and Zellweger fibroblasts and lymphoblasts and in HepG2 cells, presumably reflects mitochondrial import and processing of the precursor; the second (t1/2, 12-19 h) is present only in normal cells and presumably represents the half-life of peroxisomal HL. The half-life of mature mitochondrial HL was 14 to 19 h in both normal and Zellweger cells. Studies of the HMG-CoA lyase precursor in isolated rat mitochondria showed a rate of processing approximately 2.6-fold lower than that of the ornithine transcarbamylase precursor.
authors.affiliation: Service de Génétique Médicale, Hôpital Sainte-Justine, Université de Montréal, Montréal, Québec, Canada H3T 1C5.
authors.forename: L I
authors.initials: LI
authors.lastname: Ashmarina
authors.forename: A V
authors.initials: AV
authors.lastname: Pshezhetsky
authors.forename: S S
authors.initials: SS
authors.lastname: Branda
authors.forename: G
authors.initials: G
authors.lastname: Isaya
authors.forename: G A
authors.initials: GA
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D002374:Catalase / Q000378:metabolism; D002460:Cell Line; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000201:enzymology; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D006207:Half-Life; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008214:Lymphocytes / Q000201:enzymology; D008830:Microbodies / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D007652:Oxo-Acid-Lyases / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015211:Zellweger Syndrome / Q000201:enzymology
chemical_list: D004792:Enzyme Precursors; D011994:Recombinant Proteins; D002374:Catalase; D005969:Glutamate Dehydrogenase; D007652:Oxo-Acid-Lyases; C021410:3-hydroxy-3-methylglutaryl-coenzyme A lyase