In the "petite-negative" yeast Kluyveromyces lactis carbon catabolite repression of some cytoplasmic enzymes has been observed. However, with respect to mitochondrial enzymes, in K. lactis, unlike the case in the "petite-positive" yeast Saccharomyces cerevisiae, growth on fermentable carbon sources does not cause repression of respiratory enzymes. In this paper data are reported on carbon catabolite repression of mitochondrial enzymes in K. lactis, in particular on L- and D-lactate ferricytochrome c oxidoreductase (LCR). The L- and D-LCR (E.C. 1123, E.C. 1124) in yeast catalyze the stereospecific oxidation of D and L isomers of lactate to pyruvate. This pathway is linked to the respiratory chain, cytochrome c being the electron acceptor of the redox reaction. We demonstrate that the level of mitochondrial D- and L-LCR is controlled by the carbon source, being induced by the substrate lactate and catabolite-repressed by glucose. We cloned the structural gene for D-LCR of K. lactis (KlDLD), by complementation of growth on D,L-lactate in the S. cerevisiae strain WWF18-3D, carrying both a CYB2 disruption and the dld mutation. From the sequence analysis an open reading frame was identified that could encodea polypeptide of 579 amino acids, corresponding to a calculated molecular weight of 63,484 Da. Analysis of mRNA expression indicated that glucose repression and induction by lactate are exerted at the transcriptional level.
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