Euglena gracilis Rhodoquinone:Ubiquinone Ratio and Mitochondrial Proteome Differ under Aerobic and Anaerobic Conditions

Abstract

Euglena gracilis cells grown under aerobic and anaerobic conditions were compared for their whole cell rhodoquinone and ubiquinone content and for major protein spots contained in isolated mitochondria as assayed by two-dimensional gel electrophoresis and mass spectrometry sequencing. Anaerobically grown cells had higher rhodoquinone levels than aerobically grown cells in agreement with earlier findings indicating the need for fumarate reductase activity in anaerobic wax ester fermentation in Euglena. Microsequencing revealed components of complex III and complex IV of the respiratory chain and the E1␤ subunit of pyruvate dehydrogenase to be present in mitochondria of aerobically grown cells but lacking in mitochondria from anaerobically grown cells. No proteins were identified as specific to mitochondria from anaerobically grown cells. cDNAs for the E1␣, E2, and E3 subunits of mitochondrial pyruvate dehydrogenase were cloned and shown to be differentially expressed under aerobic and anaerobic conditions. Their expression patterns differed from that of mitochondrial pyruvate:NADP ؉ oxidoreductase, the N-terminal domain of which is pyruvate:ferredoxin oxidoreductase, an enzyme otherwise typical of hydrogenosomes, hydrogen-producing forms of mitochondria found among anaerobic protists. The Euglena mitochondrion is thus a long sought intermediate that unites biochemical properties of aerobic and anaerobic mitochondria and hydrogenosomes because it contains both pyruvate:ferredoxin oxidoreductase and rhodoquinone typical of hydrogenosomes and anaerobic mitochondria as well as pyruvate dehydrogenase and ubiquinone typical of aerobic mitochondria. Our data show that under aerobic conditions Euglena mitochondria are prepared for anaerobic function and furthermore suggest that the ancestor of mitochondria was a facultative anaerobe, segments of whose physiology have been preserved in the Euglena lineage.

Mitochondrial trans-2-Enoyl-CoA Reductase of Wax Ester Fermentation from Euglena gracilis Defines a New Family of Enzymes Involved in Lipid Synthesis

“…5, Table I). TER is expressed both under aerobic and anaerobic conditions, in line with findings from other anaerobic mitochondria, which seem to have adopted a strategy of being prepared for anaerobiosis without the need for specific enzyme induction (9,61).…”

“…Medium and Culture Conditions-Fermenter culture of E. gracilis strain Z (SAG 1224 -5/25 collection of algae Göttingen) and isolation of mitochondria was performed as described (9).…”

“…The wax ester fatty acids are synthesized from acetyl-CoA stemming from pyruvate via an unusual oxygensensitive enzyme, pyruvate:NADP ϩ oxidoreductase (6,7), the core catalytic component of which is pyruvate:ferredoxin oxidoreductase, a typical enzyme of hydrogenosomes (8). Pyruvate:NADP ϩ oxidoreductase exists in the mitochondrion alongside a classical mitochondrial pyruvate dehydrogenase complex with mRNA expression patterns converse to that of pyruvate: NADP ϩ oxidoreductase in response to hypoxia (9). Five different systems of fatty acid synthesis have been reported for E. gracilis (3).…”

“…The mitochondrial system synthesizes products of chain length 8 -18 with a majority of C14 (15,16). Synthesis of odd numbered fatty acids starts from propionylCoA, which is synthesized via the methylmalonyl-CoA pathway (17)(18)(19) and requires the participation of rhodoquinones (9).…”

Concerted Up-regulation of Aldehyde/Alcohol Dehydrogenase (ADHE) and Starch in Chlamydomonas reinhardtii Increases Survival under Dark Anoxia

“…Anaerobic respiration has also been reported, i.e. sulfur respiration in cyanobacterial species such as Oscillatoria limnetica and Microcoleus chthonoplastes (1,2), and fumarate respiration in Euglena gracilis (3,4).…”