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Volume 93, Issue 12
Displaying 1-5 of 5 articles from this issue
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Norio Muto2019 Volume 93 Issue 12 Pages 513-519
Published: December 25, 2019
Released on J-STAGE: December 31, 2020
JOURNAL OPEN ACCESSDownload PDF (1200K) -
Hiroshi Inui2019 Volume 93 Issue 12 Pages 520-530
Published: December 25, 2019
Released on J-STAGE: December 31, 2020
JOURNAL OPEN ACCESSWhen Euglena gracilis, a photosynthetic unicellular protist, was placed in anaerobic conditions, wax esters were synthesized from paramylon, a storage polysaccharide. This phenomenon is named wax ester fermentation because anaerobic Euglena cells obtain ATP through the synthesis of wax esters. In wax ester fermentation, fatty acids are synthesized essentially by the reverse reaction of β-oxidation in mitochondria, and ATP is generated by anaerobic respiration coupled with the fatty acid synthesis.
NADP+-pyruvate dehydrogenase (pyruvate:NADP+ oxidoreductase; PNO) which plays a physiologically crucial role in wax ester fermentation, was found as a novel thiamin-dependent enzyme in Euglena mitochondria. PNO, in contrast to common pyruvate dehydrogenase complex, is a homodimeric protein with a subunit molecular mass of 195.5 kDa. The enzyme consists of two functional domains: One of those is TDP domain which locates at the N-terminal side and involves thiamin diphosphate (TDP) and three [4Fe-4S] clusters as prosthetic groups, and the other is flavodomain that contains FMN and FAD. It is thought that PNO was evolved from pyruvate:ferredoxin oxidoreductase (found in anaerobic eubacteria and amitochondriate eukaryotes) by linking to a flavoprotein such as mammalian NADPH-cytochrome P450 reductase by gene fusion. PNO, similar to pyruvate:ferredoxin oxidoreductase, was quite unstable in the presence of oxygen. When Euglena, which requires thiamin for growth, was cultured under thiamin-deficient conditions, PNO protein level in cells was greatly reduced because of the instability of its apoenzyme having no TDP.View full abstractDownload PDF (1109K) -
Ryushi Kawakami2019 Volume 93 Issue 12 Pages 531-541
Published: December 25, 2019
Released on J-STAGE: December 31, 2020
JOURNAL OPEN ACCESSWe have paid much attention to screen and characterize enzymes from hyperthermophiles for analysis of their metabolic pathways of amino acids and utilization of the enzymes as the functional element for biosensor. In this review, we introduce two kinds of enzymes, FAD-dependent L-proline dehydrogenase complex and PLP-dependent amino acid racemase, from hyperthermophilic archaea. Two different FAD-dependent L-proline dehydrogenase activities were detected in the screening process of stable dye-linked dehydrogenase as specific element for electrochemical biosensor. The first enzyme found in Thermococcus profundus formed α β γ δ structure with not only proline dehydrogenase activity but also NADH dehydrogenase activity. We have succeeded in the construction of DNA sensing system using this enzyme. The second one from Pyrococcus horikoshii formed α4β4 structure and had FAD, FMN, ATP and Fe as cofactors. On the other hand, PLP-dependent amino acid racemase with broad substrate specificity was found in the process of investigation into D-amino acid utilization in the growth of P. horikoshii. Furthermore, we found another amino acid racemase specific for Ala and Ser by functional analysis of the homologs of the amino acid racemase. Because the genes of both dehydrogenases and racemases are widely conserved in the genomes of Pyrococcus and Thermococcus species, these enzymes may play important roles in the amino acid metabolisms.View full abstractDownload PDF (1565K) -
Hiroko Ikushiro, Atsushi Nagami, Tomoko Takai, Taiki Sawai, Yuki Shim ...2019 Volume 93 Issue 12 Pages 542-544
Published: December 25, 2019
Released on J-STAGE: December 31, 2020
JOURNAL OPEN ACCESSDownload PDF (1020K) -
2019 Volume 93 Issue 12 Pages 545-550
Published: December 25, 2019
Released on J-STAGE: December 31, 2020
JOURNAL OPEN ACCESSDownload PDF (936K)
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