Purification and Characterization of an α-Methylacyl-CoA Racemase from Human Liver

Authors

  • Werner Schmitz,

    1. Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität, Würzburg, Germany
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  • Christine Albers,

    1. Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität, Würzburg, Germany
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  • Ralph Fingerhut,

    1. Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität, Würzburg, Germany
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  • Ernst Conzelmann

    Corresponding author
    1. Theodor-Boveri-Institut für Biowissenschaften (Biozentrum) der Universität, Würzburg, Germany
      Correspondence to E. Conzelmann, Theodor-Boveri-Institut für Biowissenschaften, Am Hubland, D-97074 Wiirzburg, Germany
      Fax:+49 931 888 4113.
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Correspondence to E. Conzelmann, Theodor-Boveri-Institut für Biowissenschaften, Am Hubland, D-97074 Wiirzburg, Germany
Fax:+49 931 888 4113.

Abstract

A specific racemase for α-methylacyl-CoAs, which had previously been studied in rat liver [W. Schmitz, R. Fingerhut, E. Conzelmann (1994) Eur. J. Biochem. 222, 313–323], has now been demonstrated also in human tissues. The human enzyme cross-reacts with a polyclonal antiserum against the rat liver racemase. The racemase was purified from human liver some 3600-fold. It is a monomer of 47 kDa with an isolectric point of pH 6.1 and is optimally active between pH 7–8. It acts only on coenzyme A thioesters, not on free fatty acids, and accepts as substrates a wide range of α-methylacyl-CoAs, including pristanoyl-CoA and trihydroxycoprostanoyl-CoA (an intermediate in bile acid synthesis), but neither 3-methyl-branched nor linear-chain acyl-CoAs. A clear difference in subcellular localization of the enzyme was found between humans and rats: the rat enzyme co-distributed exclusively with mitochondrial marker enzymes whereas in human cells, only 10–30% of the activity was found in mitochondria, the bulk activity was located in peroxisomes. Cells from patients with general deficiency of peroxisome assembly (Zellweger syndrome) showed strongly reduced racemase activity, with only the mitochondrial share being present while the peroxisomal form was absent.

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