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Medline ® Abstracts for References 8,9

of 'Hyperimmunoglobulin D syndrome: Pathophysiology'

8
TI
Mevalonate kinase is predominantly localized in peroxisomes and is defective in patients with peroxisome deficiency disorders.
AU
Biardi L, Sreedhar A, Zokaei A, Vartak NB, Bozeat RL, Shackelford JE, Keller GA, Krisans SK
SO
J Biol Chem. 1994;269(2):1197.
 
We reported recently that mevalonate kinase (EC 2.7.1.36; ATP:mevalonate 5-phosphotransferase) that was isolated from rat liver and believed to be a cytosolic protein was localized in rat liver peroxisomes. In addition, we found that the mevalonate kinase monoclonal antibody used in the study also reacted with several other proteins present in the mitochondrial and cytosolic fractions. These findings raised the prospect of the presence of several isoenzymes of mevalonate kinase localized in different compartments of the cell. In the current study we produced four new polyclonal antibodies against different epitopes of mevalonate kinase to investigate the subcellular localization of the protein by several different approaches: (i) by analytical subcellular fractionation and immunoblotting of mevalonate kinase in the isolated subcellular fractions with the monospecific antibodies; (ii) by immunocryoelectron microscopy techniques; and (iii) by expressing the cDNA encoding mevalonate kinase in mammalian cells. The data obtained demonstrate that there is only one mevalonate kinase protein that is predominantly localized in peroxisomes. We also illustrate that the protein is targeted to and imported into peroxisomes. In addition, we show that in cells and tissues obtained from patients with peroxisomal deficiency diseases mevalonate kinase protein and its activity are severely reduced.
AD
Department of Biology, San Diego State University, California 92182.
PMID
9
TI
Differential deficiency of mevalonate kinase and phosphomevalonate kinase in patients with distinct defects in peroxisome biogenesis: evidence for a major role of peroxisomes in cholesterol biosynthesis.
AU
Wanders RJ, Romeijn GJ
SO
Biochem Biophys Res Commun. 1998;247(3):663.
 
Peroxisomes catalyze a number of essential metabolic functions especially related to lipid metabolism. There is increasing evidence suggesting that peroxisomes are also involved in the synthesis of isoprenoids via the mevalonate pathway at least in rat liver. In order to obtain independent evidence for a role of peroxisomes in isoprenoid synthesis in man, we have measured the activity of two key enzymes of the mevalonate pathway in patients suffering from certain defined defects in peroxisome biogenesis. We now report that mevalonate kinase is not only deficient in livers from Zellweger patients in which peroxisome biogenesis is defective, but also in livers from rhizomelic chondrodysplasia punctata (RCDP) Type 1 patients. In the latter group of patients there is a selective defect in peroxisome biogenesis due to a genetic defect in the PTS2-receptor, a mobile receptor-protein guiding peroxisomal proteins with a certain peroxisomal targeting signal (PTS2) to the peroxisome. Phosphomevalonate kinase was found to be strongly deficient in Zellweger patients thus suggesting that this enzyme is also peroxisomal. Taken together, our data indicate that in human liver mevalonate kinase and phosphomevalonate kinase are truly peroxisomal enzymes which strongly suggests that peroxisomes playa major role in cholesterol biosynthesis.
AD
Department of Clinical Chemistry, University of Amsterdam, Academic Medical Centre, The Netherlands. wanders@amc.uva.nl
PMID