Megumi Shimaoka
Ajinomoto
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Featured researches published by Megumi Shimaoka.
Bioscience, Biotechnology, and Biochemistry | 2005
Megumi Shimaoka; Hisashi Kawasaki; Yasuhiro Takenaka; Osamu Kurahashi; Hiroshi Matsui
Using an inosine-producing mutant of Escherichia coli, the contributions of the central carbon metabolism for overproducing inosine were investigated. Sodium gluconate instead of glucose was tested as a carbon source to increase the supply of ribose-5-phosphate through the oxidative pentose phosphate pathway. The edd (6-phosphogluconate dehydrase gene)-disrupted mutant accumulated 2.5 g/l of inosine from 48 g/l of sodium gluconate, compared with 1.4 g/l of inosine in the edd wild strain. The rpe (ribulose phosphate 3-epimerase gene)-disrupted mutant resulted in low cell growth and low inosine production on glucose and on gluconate. The disruption of pgi (glucose-6-phosphate isomerase gene) was effective for increasing the accumulation of inosine from glucose but resulted in low cell growth. The pgi-disrupted mutant accumulated 3.7 g/l of inosine from 40 g/l of glucose when 8 g/l of yeast extract was added to the medium. Furthermore, to improve effective utilization of adenine, the yicP (adenine deaminase gene)-disrupted mutant was evaluated. It showed higher inosine accumulation, of 3.7 g/l, than that of 2.8 g/l in the yicP wild strain when 4 g/l of yeast extract was added to the medium.
Bioscience, Biotechnology, and Biochemistry | 2004
Yoshiya Gunji; Nobuharu Tsujimoto; Megumi Shimaoka; Yuri Ogawa-Miyata; Shinichi Sugimoto; Hisashi Yasueda
The L-lysine biosynthetic pathway of the gram-negative obligate methylotroph Methylophilus methylotrophus AS1 was examined through characterization of the enzymes aspartokinase (AK), aspartsemialdehyde dehydrogenase, dihydrodipicolinate synthase (DDPS), dihydrodipicolinate reductase, and diaminopimelate decarboxylase. The AK was inhibited by L-threonine and by a combination of L-threonine and L-lysine, but not by L-lysine alone, and the activity of DDPS was moderately reduced by L-lysine. In an L-lysine producing mutant (G49), isolated as an S-(2-aminoethyl)-L-cysteine (lysine analog) resistant strain, both AK and DDPS were partially resistant to feedback inhibition. The ask and dapA genes encoding AK and DDPS respectively were isolated from the parental strain, AS1, and its G49 derivative. Comparison of the sequences revealed a point mutation in each of these genes in G49. The mutation in the ask gene altered aspartic acid in a key region involved in the allosteric regulation common to AKs, while a novel mutation in the dapA gene altered tyrosine-106, which was assumed to be involved in the binding of L-lysine to DDPS.
Bioscience, Biotechnology, and Biochemistry | 2006
Megumi Shimaoka; Yasuhiro Takenaka; Yoko Mihara; Osamu Kurahashi; Hisashi Kawasaki; Hiroshi Matsui
A xapA-disrupted mutant was studied to minimize hypoxanthine production and to improve inosine productivity in mutants of Escherichia coli. The xapA-disrupted mutant accumulated 5.6 g/l of inosine from 40 g/l of glucose, while the parent strain accumulated 4.6 g/l. This result indicates that xapA is activated in xapA-positive inosine-producers and that xapA disruption might be useful for improving inosine productivity.
Journal of Biotechnology | 2006
Nobuharu Tsujimoto; Yoshiya Gunji; Yuri Ogawa-Miyata; Megumi Shimaoka; Hisashi Yasueda
Archive | 1998
Hiroshi Matsui; Hisashi Kawasaki; Megumi Shimaoka; Yasuhiro Takenaka; Osamu Kurahashi
Bioscience, Biotechnology, and Biochemistry | 2001
Hiroshi Matsui; Hisashi Kawasaki; Megumi Shimaoka; Osamu Kurahashi
Archive | 2000
Yoshiya Gunji; Hisashi Yasueda; Shinichi Sugimoto; Nobuharu Tsujimoto; Megumi Shimaoka; Yuri Miyata; Manami Oba
Bioscience, Biotechnology, and Biochemistry | 2001
Hiroshi Matsui; Megumi Shimaoka; Hisashi Kawasaki; Yasuhiro Takenaka; Osamu KURAHASHl
Journal of Bioscience and Bioengineering | 2007
Megumi Shimaoka; Yasuhiro Takenaka; Osamu Kurahashi; Hisashi Kawasaki; Hiroshi Matsui
Journal of Bacteriology | 1997
Yoshihiro Usuda; Hisashi Kawasaki; Megumi Shimaoka; Takashi Utagawa