measurements for St ' iphyiococcatNuc ] ease using high sensitivity differentiul ca且 orimetry allow to determine th ' e bell shaped ftvo −dj励ensional △G ; ( 1)c巳 四 e ( Curra ei ai、 , 1994, Carra et at , , 1996) . The the 。dynamic quantities which are necessary for thethvo − dimensional energy landscape were also obtained by stUdyingthetemperaturecha ロge oftheHistidineH : ] region 倉om tHNMR spec 魄 ofnuetea $ eWt ( A 】 exandrescu et al . , 1990 ) . Pressure isanetherimportantva [iablefer

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... abi ] ity . Ne鴨 rtheless oompared to temperatUre and chemical perturbations , only few s側 dies about proteinand pressure affects are avaiEablein Ehe titeratUre . 7h」 ' ee _ dimensional energy bands・ tupes are d 巳 scribed for protcins such as chymotrypsinogen and metmyoglobin ( Haw 【 巳 y, 197 且 , Zipp & Kauzmann, 置 973> , In ourpresenE research we intrDduce the o ロ・ line high ・ pressure glass tube mcthodoriginally repartedby Yamada 〔 Yamada etal . , 工 994)to deterrnine a th」 』 ee − dimensionat energy landscape by NMR . Uti ] izing th¢ Histidine Peaks at diff ¢ r¢ ntpressuresand Lemperutures , wo have been abie nol on ] y 巳 o achieve 1he thermodynamie quantities men [ ioned め ov じ but n且 so to We started a saries ef crystallographic stUdies on the 【 esponsible factors causing hyper− thermostabili [ y of the enzymes fre 皿 the hyper 山 ermophilic organis 皿 s . il tbe P匸esent study , we foeused on the structure −stability relat 孟 onship ofglutamate debydrogenase ( GDH )frem hyperthermophi 旦 ic archaeon , Thermococczas projUndus. lhe purified recomb 孟 nan 匸enzyme was success 血 Uy crystallized in the presence of both polyethylene glyco 玉 8000, The crystal belonged to[he monoclin 童 e space greup P2 , , and the unit cell dirnensions were a =ll2. 99, b =亘63, 70, c =133. 07 A, and β =置13. 46°at 110 K . and centained 。ne hexamer ef tbe enzyrne ( Mw = 280 kDa ) , which was the physiolegical fUnctional unit , 童 n its crystall 。 gmpbic asy e 面 c uni 匸. X −ray d . iffraction intensity data ロ were collected up to a resolution of 2, 25 A with good stat孟 stics at the BL44B2 ( 1)beamline ef SPring − 8 ( the completeness was 99. 7% . and the R . 、 r , n . i value was O. 072) . Tbc crystal s し ructure of [ he hcxamcr was so ヒ ved by us 正 ng the molecular repiacement methed . The crystallographic refinement is undcr way ( current R = 0. 192 fc ) r the refiectiens between 8、 0 − 2、 25Aresoluti Ω n ) 、 Based omhe S 血 ctural model , we would 迅 二 e to dtscuss 山e responsible factors fbr山e ther皿 【 )sLabHity . In additiQn , w 巳 describe the snapsho 匠 s of charac 匸 erist 主 c domain closu [ e 皿 o 癒 ons 創nd a folding− un 魚 ) lding tr皿 s 正 tion observed in 仁 he preSent CrySta 「 StrUCtUre analySis .