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Articles by K. Kita
Total Records ( 3 ) for K. Kita
  K. Kita , S. Okada , H. Sekino , K. Imou , S. Yokoyama and T. Amano
  Botryococcus braunii, a green colonial microalga, is an unusually rich renewable source of hydrocarbons. In this study, wet microalgae harvest was thermally pretreated to enhance hydrocarbon recovery using a solvent extraction process. Samples containing a mixture of B. braunii and water were kept below 100  °C for 10 min. The observed hydrocarbon recovery was 97.8% at 90 °C. The extraction results suggest that the energy-intensive concentration and drying processes of the harvest could be eliminated. The proposed thermal pretreatment would revolutionize the conventional downstream processes.
  T Mogi , T Kawakami , H Arai , Y Igarashi , K Matsushita , M Mori , K Shiomi , S Omura , S Harada and K. Kita
 

To identify antibiotics targeting to respiratory enzymes, we carried out matrix screening of a structurally varied natural compound library with Pseudomonas aeruginosa membrane-bound respiratory enzymes. We identified a succinate dehydrogenase inhibitor, siccanin (IC50, 0.9 µM), which is a potent antibiotic against some pathogenic fungi like Trichophyton mentagrophytes and inhibits their mitochondrial succinate dehydrogenase. We found that siccanin was effective against enzymes from P. aeruginosa, P. putida, rat and mouse mitochondria but ineffective or less effective against Escherichia coli, Corynebacterium glutamicum, and porcine mitochondria enzyme. Action mode was mixed-type for quinone-dependent activity and noncompetitive for succinate-dependent activity, indicating the proximity of the inhibitor-binding site to the quinone-binding site. Species-selective inhibition by siccanin is unique among succinate dehydrogenase inhibitors, and thus siccanin is a potential lead compound for new chemotherapeutics.

  T Mogi , Y Murase , M Mori , K Shiomi , S Omura , M. P Paranagama and K. Kita
 

Tuberculosis is the leading cause of death due to a single infectious agent in the world and the emergence of multidrug-resistant strains prompted us to develop new drugs with novel targets and mechanism. Here, we screened a natural antibiotics library with Mycobacterium smegmatis membrane-bound dehydrogenases and identified polymyxin B (cationic decapeptide) and nanaomycin A (naphtoquinone derivative) as inhibitors of alternative NADH dehydrogenase [50% inhibitory concentration (IC50) values of 1.6 and 31 µg/ml, respectively] and malate: quinone oxidoreductase (IC50 values of 4.2 and 49 µg/ml, respectively). Kinetic analysis on inhibition by polymyxin B showed that the primary site of action was the quinone-binding site. Because of the similarity in Km value for ubiquinone-1 and inhibitor sensitivity, we examined amino acid sequences of actinobacterial enzymes and found possible binding sites for l-malate and quinones. Proposed mechanisms of polymyxin B and nanaomycin A for the bacteriocidal activity were the destruction of bacterial membranes and production of reactive oxygen species, respectively, while this study revealed their inhibitory activity on bacterial membrane-bound dehydrogenases. Screening of the library with bacterial respiratory enzymes resulted in unprecedented findings, so we are hoping that continuing efforts could identify lead compounds for new drugs targeting to mycobacterial respiratory enzymes.

 
 
 
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