J. Biochem, 1995, Vol. 118, No. 3 587-592
© 1995 Japanese Biochemical Society
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Properties of Glutamate Dehydrogenase and Its Involvement in Alanine Production in a Hyperthermophilic Archaeon, Thermococcus profundus1
,2
*Laboratory of Microbiology, The Institute of Physical and Chemical Research (RIKEN), 2–1 Hirosawa, Wako, Saitama 351-01
DEEP-STAR Group, Japan Marine Science and Technology Center 2-15 Natsushima-cho, Yokosuka, Kanagawa 237
Laboratory of Biochemistry, College of Science, Rikkyo (St. Paul's) University Nishi-Ikebukuro, Toshima-ku, Tokyo 171
2To whom correspondence should be addressed at the present address: Department of Applied Biological Sciences, School of Agricultural Sciences, Nagoya University, Chikusa-ku, Nagoya, Aichi 464–01. E mail: i45557a{at}nucc.cc.nagoya-u.ac.jp
Thermococcus profundus, a hyperthermophilic archaeon, did not exhibit detectable glutamine synthetase activity, although the organism possessed an extraordinarily high level of glutamate dehydrogenase (GDH), the content of which reached over 10% of total soluble proteins. This GDH was purified to homogeneity. The enzyme had a molecular weight of 263, 000 and was composed of six homogeneous subunits of molecular weight 43, 000. The enzyme was extremely thermostable with a half life of 1 h at 90°C. Circular dichroism (CD) spectra of the enzyme revealed gradual unfolding of 
-helices upon exposure to increasing temperature. The enzyme reaction was strongly biased toward glutamate formation. T.profundus excreted L-alanine into the medium, and the concentration reached 1.5mM. High activity of alanine aminotransferase (AAT) was present in the cells, while no alanine dehydrogenase activity was detected. The alanine formation may be initiated by ammonia uptake by GDH followed by aminotransfer from glutamate to pyruvate by AAT.
1This work was partially supported by a grant for the Biodesign Program to T. Kudo and a special grant for Promotion of Research to T. Kobayashi from the Institute of Physical and Chemical Research (RIKEN).
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