Debaryomyces pathway composes by complexes I-IV, the electron

Debaryomyces
hansenii,
a marine, osmotolerant and oleaginous yeast, has a
branched mitochondrial respiratory chain (Breuer U et al., 2006). Besides the
canonical pathway composes by complexes I-IV, the electron flux can be driven
through alternative routes that include an
alternative oxidase resistant to cyanide (AOX), an external NADH
dehydrogenase (NDH2e) and a glycerol-phosphate dehydrogenase
(MitGPDH)(Cabrera-Orefice A. et al.,
2014)
In yeasts, the physiological function of alternative oxidoreductases
is not entirely known but probably avoids electron flux saturation on the
mitochondrial cytochrome pathway (Guerrero-Castillo et al., 2011)
establishing a Radical Oxygen Species-preventing mechanism (El-Khoury R. et
al., 2013). Protection from ROS could be explained due to this redox enzymes
maintain a high oxygen consumption without a proton pumping activity,
uncoupling the oxidative phosphorylation despite a raised transmembrane
potential (Joseph-Horne et al., 2001).
In contrast to NDH2e and MitGPDH
constitutive expression (Cabrera-Orefice et al., 2014), AOX appears at the
stationary growth phase (Veiga et al., 2003). Nevertheless, data from our
group suggest that the expression of AOX may also depend on the carbon source
added to the culture medium.
Therefore, we analysed cyanide-resistant
respiration (CRR) in intact yeast cells cultivated on different carbon
sources.
Here, we studied both cytochrome-
and alternative-pathway related oxygen consumption
differences in whole yeast cells grown on different carbon sources. In lactate or succinate supplied media, AOX was fully active in all growth
phases. By contrast, in glucose- or galactose-containing media, AOX activity
was detected until the late exponential phase. Since both lactate and
succinate are considered as substrates which promote respiration, their
donated electrons may saturate cytochrome route, and AOX serves as an
alternative route. However, in glycerol-containing media, AOX activity was poorly detected during all the growth. This result was
unanticipated because glycerol is amply used in respiratory culture media and
a lactate/succinate-grown cells behaviour will be expected. Besides,
glucose-grown cells exhibited the most significant biomass yield.
Nevertheless, biomass yield in glycerol-grown cells was higher than in the
other three carbon sources. This indicates that a considerable amount of
glycerol was used in biosynthetic pathways. In this condition, D. hansenii probably did not express
AOX to keep the Oxidative Phosphorylation system in a highly coupled mode and
support ATP needs for glycerol-promoted lipid biosynthesis. This finding
result attractive as D. hansenii
would be useful for biotechnological targets such as biodiesel production.

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