Browsing by Author "Akhmanova, Anna"

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    Cytosolic Enzymes with a Mitochondrial Ancestry from the Anaerobic Chytrid Piromyces Sp. E2. Mol Microbiol 30:1017-1027
    (1998) Akhmanova, Anna; Voncken, Frank; Harhangi, Harry R.; Hosea, Ken M.; Vogels, Godfried D.; Hackstein, Johannes H. P.
    The anaerobic chytrid Piromyces sp. E2 lacks mitochondria, but contains hydrogen-producing organelles, the hydrogenosomes. We are interested in how the adaptation to anaerobiosis influenced enzyme compartmentalization in this organism. Random sequencing of a cDNA library from Piromyces sp. E2 resulted in the isolation of cDNAs encoding malate dehydrogenase, aconitase and acetohydroxyacid reductoisomerase. Phylogenetic analysis of the deduced amino acid sequences revealed that they are closely related to their mitochondrial homologues from aerobic eukaryotes. However, the deduced sequences lack N-terminal extensions, which function as mitochondrial leader sequences in the corresponding mitochondrial enzymes from aerobic eukaryotes. Subcellular fractionation and enzyme assays confirmed that the corresponding enzymes are located in the cytosol. As anaerobic chytrids evolved from aerobic, mitochondria-bearing ancestors, we suggest that, in the course of the adaptation from an aerobic to an anaerobic lifestyle, mitochondrial enzymes were retargeted to the cytosol with the concomitant loss of their N-terminal leader sequences.
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    A Hydrogenosome with Pyruvate Formate-Lyase: Anaerobic Chytrid Fungi Use an Alternative Route for Pyruvate Catabolism. Mol Microbiol 32:1103-1114
    (Wiley, 1999) Akhmanova, Anna; Voncken, Frank; Hosea, Ken M.; Harhangi, H.; Keltjens, J. T.; Op Den Camp, H. J.; Vogels, G. D.; Hackstein, Johannes H. P.
    The chytrid fungi Piromyces sp. E2 and Neocallimastix sp. L2 are obligatory amitochondriate anaerobes that possesshydrogenosomes.Hydrogenosomes arehighly specialized organelles engaged in anaerobic carbon metabolism; they generate molecular hydrogen and ATP. Here, we show for the ®rst time that chytrid hydrogenosomes use pyruvate formate-lyase (PFL) and not pyruvate:ferredoxin oxidoreductase (PFO) for pyruvate catabolism, unlike all other hydrogenosomes studied to date. Chytrid PFLs are encoded by a multigene family and are abundantly expressed in Piromyces sp. E2 and Neocallimastix sp. L2. Western blotting after cellular fractionation, proteinase K protection assays and determinations of enzyme activities reveal that PFL is present in the hydrogenosomes of Piromyces sp. E2. The main route of the hydrogenosomal carbon metabolism involves PFL; the formation of equimolar amounts of formate and acetate by isolated hydrogenosomes excludes a signi®cant contribution by PFO. Our data support the assumption that chytrid hydrogenosomes are unique and argue for a polyphyletic origin of these organelles.