The metabolic role of yeast carnitine acetyl transferases.
Sven Kroppenstedt (1), Jaco Franken (1), Isak S. Pretorius (2), Jan H. Swiegers (2), Florian F. Bauer (1)
(1) Inst. Wine Biotechnology, Stellenbosch University, Victoriastreet, Stellenbosch, 7602, South Africa;
(2) Australian Wine Research Institute, Waite Road , Urrbrae Glen Osmond , Adelaide, SA 5064 , Australia
In eukaryotic cells, L-carnitine plays an essential role in the shuttling of activated acyl residues between cellular compartments. In the yeast Saccharomyces cerevisiae, the shuttle is required under certain growth conditions to transfer activated acetyl residues from the peroxisomes and the cytoplasm to the mitochondria for energy generation. Three carnitine acetyl transferases (CATs), Yat1p, Yat2p and Cat2p, are essential elements of the shuttle and catalyze the transfer of activated acetyl residues between coenzyme A and carnitine. However, the exact metabolic role of each of the three enzymes remains unclear. Here we show that despite extensive amino acid sequence homology between these proteins, each enzyme fulfills clearly distinct metabolic functions, since deletion of any one of the genes cannot be phenotypically cross-complemented by overexpression of any of the two remaining CATs. Nevertheless, the phenotypes of mutants with single, double, or triple deletions of these genes are identical in all conditions tested. The sub-cellular localization of each enzyme, established through the use of GFP-tagged proteins, confirms that Cat2p is localized to both the peroxisomes and the mitochondria and that Yat1p is associated with the mitochondria. The data suggest that Yat2p is localized in the cytoplasm. The data also show that the three genes show similar, but not identical transcription profiles, and that enzymatic activities vary with growth conditions.
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