Some parameters affecting respiratory control in Azotobacter vinelandii membranes

AbstractRCI :respiratory control index (state 3/state 4 rate of oxygen uptake)m-C1 CCP: carbonylcyanide m-chlorophenyl hydrazoneHQNO : 2-n-heptyl-4-hydroxyquinoline-N-oxidePIPES: piperazine-N,N′-bis 2-ethane sulphonic aci

The relationship between redox enzyme activity and electrochemical potential—cellular and mechanistic implications from protein film electrochemistry

In protein film electrochemistry a redox protein of interest is studied as an electroactive film adsorbed on an electrode surface. For redox enzymes this configuration allows quantification of the relationship between catalytic activity and electrochemical potential. Considered as a function of enzyme environment, i.e., pH, substrate concentration etc., the activity–potential relationship provides a fingerprint of activity unique to a given enzyme. Here we consider the nature of the activity–potential relationship in terms of both its cellular impact and its origin in the structure and catalytic mechanism of the enzyme. We propose that the activity–potential relationship of a redox enzyme is tuned to facilitate cellular function and highlight opportunities to test this hypothesis through computational, structural, biochemical and cellular studies

Seasonal Variation in the Hepatoproteome of the Dehydrationand Freeze-Tolerant Wood Frog, Rana sylvatica

Winter’s advent invokes physiological adjustments that permit temperate ectotherms to cope with stresses such as food shortage, water deprivation, hypoxia, and hypothermia. We used liquid chromatography (LC) in combination with tandem mass spectrometry (MS/MS) quantitative isobaric (iTRAQ™) peptide mapping to assess variation in the abundance of hepatic proteins in summer- and winter-acclimatized wood frogs (Rana sylvatica), a northerly-distributed species that tolerates extreme dehydration and tissue freezing during hibernation. Thirty-three unique proteins exhibited strong seasonal lability. Livers of winter frogs had relatively high levels of proteins involved in cytoprotection, including heat-shock proteins and an antioxidant, and a reduced abundance of proteins involved in cell proliferation, protein synthesis, and mitochondrial function. They also exhibited altered levels of certain metabolic enzymes that participate in the biochemical reorganization associated with aphagia and reliance on energy reserves, as well as the freezing mobilization and post-thaw recovery of glucose, an important cryoprotective solute in freezing adaptation

Production, characterization and determination of the real catalytic properties of the putative ‘succinate dehydrogenase’ from Wolinella succinogenes

Both the genomes of the epsilonproteobacteria Wolinella succinogenes and Campylobacter jejuni contain operons (sdhABE) that encode for so far uncharacterized enzyme complexes annotated as ‘non-classical’ succinate:quinone reductases (SQRs). However, the role of such an enzyme ostensibly involved in aerobic respiration in an anaerobic organism such as W. succinogenes has hitherto been unknown. We have established the first genetic system for the manipulation and production of a member of the non-classical succinate:quinone oxidoreductase family. Biochemical characterization of the W. succinogenes enzyme reveals that the putative SQR is in fact a novel methylmenaquinol:fumarate reductase (MFR) with no detectable succinate oxidation activity, clearly indicative of its involvement in anaerobic metabolism. We demonstrate that the hydrophilic subunits of the MFR complex are, in contrast to all other previously characterized members of the superfamily, exported into the periplasm via the twin-arginine translocation (tat)-pathway. Furthermore we show that a single amino acid exchange (Ala86→His) in the flavoprotein of that enzyme complex is the only additional requirement for the covalent binding of the otherwise non-covalently bound FAD. Our results provide an explanation for the previously published puzzling observation that the C. jejuni sdhABE operon is upregulated in an oxygen-limited environment as compared with microaerophilic laboratory conditions