| Project/Area Number |
14580632
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural biochemistry
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| Research Institution | Osaka Medical College |
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Principal Investigator |
MIZUGUCHI Kiroyuki Osaka Medical College, Faculty of Medicine, Research Associate, 医学部, 助手 (40247838)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2003: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2002: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | Aminotransferase / Pyridoxal 5'-phosphate / Schiff base pK_a / Reaction mechanism / Strain / ヒスチジノールリン酸アミノ基転移酵素 / グルタミンアミノ基転移酵素 / ピリドキサルリン酸 / シッフ塩基 pK_a |
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| Research Abstract |
HPAT followed a Ping-Pong Bi Bi kinetic mechanism. The PLP-form HPAT showed pH dependent absorption and CD spectral changes with maxima at 340 nm at high pH and 420 nm at loW pH (pK_a=6.6). Absorption spectral changes of the glutarate-or 2-methylglutamate-bound wild type enzyme indicated that the Schiff base pK_a of the Michaelis complex and the external aldimine were increased. Absorption spectra of K214A mutant enzyme in the presence of 2-methylglutamate demonstrated that the intrinsic Schiff base pK_a of the external aldimine was much elevated. The pK_a value of the methylamine-substituted K214A mutant enzyme was increased from 6.6 to 10.6. Mutation of Asn157 to Ala increased the pK_a to 9.2. Data indicate that the strain of the Schiff base is the principal factor to decrease the pK_a in HPAT, and is crucial for the subsequent increase in the Schiff base pK_a during catalysis. It is suggested that the Schiff base strain mechanism is a common to the Subgroup I aminotransferases.
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