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Articles by T Soga
Total Records ( 3 ) for T Soga
  T Kato , S Niizuma , Y Inuzuka , T Kawashima , J Okuda , Y Tamaki , Y Iwanaga , M Narazaki , T Matsuda , T Soga , T Kita , T Kimura and T. Shioi
  Background—

Congestive heart failure (CHF) is associated with a change in cardiac energy metabolism. However, the mechanism by which this change is induced and causes the progression of CHF is unclear.

Methods and Results—

We analyzed the cardiac energy metabolism of Dahl salt-sensitive rats fed a high-salt diet, which showed a distinct transition from compensated left ventricular hypertrophy to CHF. Glucose uptake increased at the left ventricular hypertrophy stage, and glucose uptake further increased and fatty acid uptake decreased at the CHF stage. The gene expression related to glycolysis, fatty acid oxidation, and mitochondrial function was preserved at the left ventricular hypertrophy stage but decreased at the CHF stage and was associated with decreases in levels of transcriptional regulators. In a comprehensive metabolome analysis, the pentose phosphate pathway that regulates the cellular redox state was found to be activated at the CHF stage. Dichloroacetate (DCA), a compound known to enhance glucose oxidation, increased energy reserves and glucose uptake. DCA improved cardiac function and the survival of the animals. DCA activated the pentose phosphate pathway in the rat heart. DCA activated the pentose phosphate pathway, decreased oxidative stress, and prevented cell death of cultured cardiomyocytes.

Conclusions—

Left ventricular hypertrophy or CHF is associated with a distinct change in the metabolic profile of the heart. DCA attenuated the transition associated with increased energy reserves, activation of the pentose phosphate pathway, and reduced oxidative stress.

  T Ooga , Y Ohashi , S Kuramitsu , Y Koyama , M Tomita , T Soga and R. Masui
 

A major bacterial alarmone, guanosine 3',5'-bispyrophosphate (ppGpp), controls cellular growth under conditions of nutritional starvation. For most bacteria, intracellular ppGpp levels are tightly controlled by the synthesis/degradation cycle of RelA and SpoT activities. This study shows a novel ppGpp regulatory protein governing the cellular growth of Thermus thermophilus, Ndx8, a member of the Nudix pyrophosphatase family that degrades ppGpp to yield guanosine 3',5'-bisphosphate. The ndx8-null mutant strain exhibited early stage growth arrest accompanied by the stationary phase-specific morphologies and global transcriptional modulation under nutritionally defined conditions. Several possible substrate compounds of Ndx8, which specifically accumulated in the ndx8 mutant cells, were identified by employing a capillary electrophoresis time-of-flight mass spectrometry-based metabolomics approach. Among them, the hydrolytic activity of Ndx8 for ppGpp was significant not only in vitro but also in vivo. Finally, the elimination of ppGpp synthetic activity suppressed the observed phenotype of the ndx8 mutation, suggesting that the function of Ndx8 as a growth regulator is involved in ppGpp accumulation, which is thought to act as a trigger of the growth phase transition. These results suggest a novel mechanism of ppGpp-mediated growth control by the functional relay between Ndx8 and SpoT activity as ppGpp scavengers.

  N Saito , M Robert , H Kochi , G Matsuo , Y Kakazu , T Soga and M. Tomita
 

The search for novel enzymes and enzymatic activities is important to map out all metabolic activities and reveal cellular metabolic processes in a more exhaustive manner. Here we present biochemical and physiological evidence for the function of the uncharacterized protein YihU in Escherichia coli using metabolite profiling by capillary electrophoresis time-of-flight mass spectrometry. To detect enzymatic activity and simultaneously identify possible substrates and products of the putative enzyme, we profiled a complex mixture of metabolites in the presence or absence of YihU. In this manner, succinic semialdehyde was identified as a substrate for YihU. The purified YihU protein catalyzed in vitro the NADH-dependent reduction of succinic semialdehyde to -hydroxybutyrate. Moreover, a yihU deletion mutant displayed reduced tolerance to the cytotoxic effects of exogenous addition of succinic semialdehyde. Profiling of intracellular metabolites following treatment of E. coli with succinic semialdehyde supports the existence of a YihU-catalyzed reduction of succinic semialdehyde to -hydroxybutyrate in addition to its known oxidation to succinate and through the tricarboxylic acid cycle. These findings suggest that YihU is a novel -hydroxybutyrate dehydrogenase involved in the metabolism of succinic semialdehyde, and other potentially toxic intermediates that may accumulate under stress conditions in E. coli.

 
 
 
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