AS‐30D hepatoma cells, a highly oxidative and fast‐growing tumor line, showed glucose‐induced and fructose‐induced inhibition of oxidative phosphorylation (the Crabtree effect) of 54% and 34%, respectively. To advance the understanding of the underlying mechanism of this process, the effect of 5 mm glucose or 10 mm fructose on the intracellular concentration of several metabolites was determined. The addition of glucose or fructose lowered intracellular P_i (40%), and ATP (53%) concentrations, and decreased cytosolic pH (from 7.2 to 6.8). Glucose and fructose increased the content of AMP (30%), glucose 6‐phosphate, fructose 6‐phosphate and fructose 1,6‐bisphosphate (15, 13 and 50 times, respectively). The cytosolic concentrations of Ca²⁺ and Mg²⁺ were not modified. The addition of galactose or glycerol did not modify the concentrations of the metabolites. Mitochondria isolated from AS‐30D cells, incubated in media with low P_i (0.6 mm) at pH 6.8, exhibited a 40% inhibition of oxidative phosphorylation. The data suggest that the Crabtree effect is the result of several small metabolic changes promoted by addition of exogenous glucose or fructose.

The sodium -pumping NADH: ubiquinone oxidoreductase (Na⁺-NQR) is the main ion pump and the primary entry site for electrons into the respiratory chain of many different types of pathogenic bacteria. This enzymatic complex creates a transmembrane gradient of sodium that is used by the cell to sustain ionic homeostasis, nutrient transport, ATP synthesis, flagellum rotation and other essential processes. Comparative genomics data demonstrate that the nqr operon, which encodes all Na⁺-NQR subunits, is found in a large variety of bacterial lineages with different habitats and metabolic strategies. Here we studied the distribution, origin and evolution of this enzymatic complex. The molecular phylogenetic analyses and the organizations of the nqr operon indicate that Na⁺-NQR evolved within the Chlorobi/Bacteroidetes group, after the duplication and subsequent neofunctionalization of the operon that encodes the homolog RNF complex. Subsequently, the nqr operon dispersed through multiple horizontal transfer events to other bacterial lineages such as Chlamydiae, Planctomyces and α, β, γ and δ -proteobacteria. Considering the biochemical properties of the Na⁺-NQR complex and its physiological role in different bacteria, we propose a detailed scenario to explain the molecular mechanisms that gave rise to its novel redox- dependent sodium -pumping activity. Our model postulates that the evolution of the Na⁺-NQR complex involved a functional divergence from its RNF homolog, following the duplication of the rnf operon, the loss of the rnfB gene and the recruitment of the reductase subunit of an aromatic monooxygenase.

Mitochondrial complexes I, III(2), and IV from human cytotrophoblast and syncytiotrophoblast associate to form supercomplexes or respirasomes, with the following stoichiometries: I(1):(III(2))(1) and I(1):(III(2))(1-2):IV(1-4). The content of respirasomes was similar in both cell types after isolating mitochondria. However, syncytiotrophoblast mitochondria possess low levels of dimeric complex V and do not have orthodox cristae morphology. In contrast, cytotrophoblast mitochondria show normal cristae morphology and a higher content of ATP synthase dimer. Consistent with the dimerizing role of the ATPase inhibitory protein (IF(1)) (García, J. J., Morales-Ríos, E., Cortés-Hernandez, P., and Rodríguez-Zavala, J. S. (2006) Biochemistry 45, 12695-12703), higher relative amounts of IF(1) were observed in cytotrophoblast when compared with syncytiotrophoblast mitochondria. Therefore, there is a correlation between dimerization of complex V, IF(1) expression, and the morphology of mitochondrial cristae in human placental mitochondria. The possible relationship between cristae architecture and the physiological function of the syncytiotrophoblast mitochondria is discussed.