http://www.biochemj.org Biochemical Journal RSS feed -- BJ Energy Immediate Publications 0264-6021 1470-8728 Biochemical Journal http://www.biochemj.org/images/BJ_Name.gif http://www.biochemj.org http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20120248 2+ is thought to be central to the channel’s ability to regulate reactive oxygen species (ROS) production. However, channel-mediated entry of Mg²⁺ and Zn²⁺ have also been implicated in cell death. Here we show that depletion of TRPM7 by RNA interference in fibroblasts increases cell resistance to apoptotic stimuli by decreasing ROS levels in a Mg²⁺-dependent manner. Depletion of TRPM7 lowered cellular Mg²⁺, decreased the concentration of ROS and lessened p38 MAP kinase and JNK activation as well as decreased caspase-3 activation and PARP cleavage in response to apoptotic stimuli. Re-expression of TRPM7 or of a kinase-inactive mutant of TRPM7 in TRPM7-knockdown cells increased cellular Mg²⁺ and ROS levels, as did expression of the Mg²⁺ transporter SLC41A2. In addition, expression of SLC41A2 increased TRPM7-knockdown cells’ sensitivity to apoptotic stimuli as well as boosted ROS generation in response to cell stress. Together these data uncover an essential role for Mg²⁺ in TRPM7’s control of cell survival and in the regulation of cellular ROS levels.]]> H Chen, L Su, O González-Pagán, J D. Overton, L W. Runnels 2012-05-15T15:52:01Z doi:10.1042/BJ20120248 Portland Press Limited 2012-05-15 BJ Cell http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20112142 succination of proteins, increases in adipocytes grown in high glucose medium and in adipose tissues of type 2 diabetic mice. However, the metabolic mechanisms leading to increased fumarate and succination of protein in the adipocyte are unknown. Treatment of 3T3 cells with high glucose (30 mM vs. 5 mM) caused a significant increase in cellular ATP/ADP, NADH/NAD⁺, and the mitochondrial membrane potential. There was also a significant increase in cellular fumarate concentration and succination of proteins, which may be attributed to the increase in NADH/NAD⁺ and subsequent inhibition of Krebs cycle NAD⁺-dependent dehydrogenases. Chemical uncouplers, which dissipated the mitochondrial membrane potential and reduced the NADH/NAD­⁺ ratio, also decreased fumarate concentration and protein succination. High glucose plus metformin, an inhibitor of Complex I in the electron transport chain, caused an increase in fumarate and succination of protein. Thus, excess fuel supply (glucotoxicity) appears to create a pseudohypoxic environment (high NADH/NAD⁺ without hypoxia), which drives the increase in succination of protein. We propose that increased succination of proteins is an early marker of glucotoxicity and mitochondrial stress in adipose tissue in diabetes.]]> N Frizzell, S A Thomas, J A Carson, J W Baynes 2012-04-24T10:00:12Z doi:10.1042/BJ20112142 Portland Press Limited 2012-04-24 BJ Metabolism http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20111978 Symplocarpus renifolius and Arum maculatum are known to produce significant heat during the course of their floral development but using different regulatory mechanisms i.e., homoeothermic versus transient thermogenesis. To further clarify the molecular basis of species-specific thermogenesis in plants, we have here analyzed the native structures and expression patterns of the mitochondrial respiratory components in S. renifolius and A. maculatum. Our comparative analysis using blue native polyacrylamide gel electrophoresis combined with nano LC-MS/MS has revealed that the constituents of the respiratory complexes in both plants were basically similar, but that several mitochondrial components appeared to be differently expressed in their thermogenic organs. Namely, complex II in S. renifolius was detected as a 340 kDa product, suggesting an oligomeric or supramolecular structure in vivo. Moreover, the expression of an external NAD(P)H dehydrogenase was found to be higher in A. maculatum than in S. renifolius whereas an internal NAD(P)H dehydrogenase was expressed to a similar level in both species. Alternative oxidase was detected as smear-like signals that were elongated on the first dimension with a peak at around 200 kDa in both species. The significance and implication of these data are discussed in terms of thermoregulation in plants.]]> Y Kakizaki, A L. Moore, K Ito 2012-04-19T09:46:25Z doi:10.1042/BJ20111978 Portland Press Limited 2012-04-19 BJ Plant http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20111984 Neisseria species N. meningitidis and N. gonorrhoeae are able to respire in the absence of oxygen, using nitrite as an alternative electron acceptor. Nitrite reductase (encoded by aniA) is tightly regulated by four transcriptional regulators: FNR, NarP, FUR and NsrR. The four regulators control expression of aniA in N. meningitidis by binding to specific and distinct regions of the promoter. We show here that FUR and NarP are both required for induction of expression of aniA in N. meningitidis, and that they bind adjacent to one another in a non-cooperative manner. Activation via FUR/NarP is dependent on their topological arrangement relative to the RNA polymerase binding site. Analysis of the sequence of the aniA promoters from multiple N. meningitidis and N. gonorrhoeae strains indicates that there are species-specific single nucleotide polymorphisms, in regions predicted to be important for regulator binding. These sequence differences alter both the in vitro DNA binding and the promoter activation in intact cells by key activators FNR (oxygen sensor) and NarP (which is activated by nitrite in N. meningitidis). The weak relative binding of FNR to the N. gonorrhoeae aniA promoter (compared to N. meningitidis) is compensated for by a higher affinity of the gonococcal aniA promoter for NarP. Despite containing nearly identical genes for catalysing and regulating denitrification, variations in the promoter for the aniA gene appear to have been selected to enable the two pathogens to tune differentially their responses to environmental variables during the aerobic-anaerobic switch.]]> J Edwards, D Quinn, K Rowbottom, J L Whittingham, M J. Thomson, J W. B. Moir 2012-04-18T11:25:28Z doi:10.1042/BJ20111984 Portland Press Limited 2012-04-18 BJ Gene http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20120294 A R Diers, K A Broniowska, C Chang, N Hogg 2012-03-30T09:49:50Z doi:10.1042/BJ20120294 Portland Press Limited 2012-03-30 BJ Energy http://www.biochemj.org/bj/imps/refer.htm?MSID=BJ20120197 Shewanella oneidensis MR-1 identifies three low-spin His/His coordinated c-hemes and a single high-spin c-heme with His/H₂O coordination lying adjacent to the quinol binding site. At pH 7, binding of the menaquinol analogue, 2-heptyl-4-hydroxyquinoline-N-oxide, does not alter the mid-point potentials of the high-spin (ca. -240 mV) and low-spin (ca. -110, -190 and -265 mV) hemes that appear biased to transfer electrons from the high- to low-spin centres following quinol oxidation. CymA is reduced with menadiol (E_m -80 mV) in the presence of NADH (E_m -320 mV) and an NADH:menadione oxidoreductase, but not by menadiol alone. In cytoplasmic membranes reduction of CymA may then require the thermodynamic driving force from NADH, formate or H₂ oxidation as the redox poise of the menaquinol pool in isolation is insufficient. Spectroscopic studies suggest that CymA requires a non-heme cofactor for quinol oxidation and that the reduced enzyme forms a 1:1 complex with its redox partner Fcc₃. The implications for CymA supporting the respiratory flexibility of shewanellae are discussed.]]> S J Marritt, T G Lowe, J Bye, D G G McMillan, L Shi, J Fredrickson, J Zachara, D J Richardson, M R Cheesman, L J C Jeuken, J N Butt 2012-03-29T14:13:17Z doi:10.1042/BJ20120197 Portland Press Limited 2012-03-29 BJ Energy