- 作者: 張固剛; 黃德美; 武家安
- 作者服務機構: 國防醫學院生物化學研究所
- 中文摘要:
鴿肝蘋界酸?催化的反應與-pK 值為 6.7 的胺酸基之游離情形有關。此pK 值不受溫度改變之影響,故可能為羧
基。蘋果酸?在 pH 6.0及25 C時與 N-ethyl-5-phenylisoxazolium-3'-sulfonate 反應失去活性。以 N-甲基羥胺處理可恢
復?活性,而甘胺酸乙酯則否。反應前加入Mn , NADP 及蘋果酸可降低?失活速率,表示?的失活是由於?活性中
心某重要胺酸基被修飾結果,而各項證據顯示此胺酸為麩胺酸或天門冬按胺酸。?經修飾後與 NADP ,Mn ,丙酮酸或蘋
果酸等基質的結合皆未受影響。此羧基的真正功能可能係參與催化反應。我們根據歷年來的研究結果提出此?的作用機
轉模式以供進一步研究的參考。
2 - 英文摘要: The maximum velocity of the reaction catalyzed by the pigeon liver malic enzyme depends on theionization of a functional group of pK 6.7·This pK value is independent of temperature within the range30 ~ 49 C, suggesting the ionization of a carboxyl group. The enzyme activity is inactivated by N-ethyl-5-phenylisoxazolium-3'-sulfonate (Woodward reagent K) at pH 6.0 and 25 C. N-Methylhydroxamine re-generates the enzymatic activity whereas glycine ethyl ester does not. The addition of Mn +,NADP , andL-malate to the incubation mixture decreases the inactivation rate, suggesting that the reaction takes placein the active center. The binding capacities of the modified enzyme with NADP , L-malate, pyruvate, andMn are not impaired. The kinetic and chemical evidence indicates that the inactivation is due to the mo-dification of a carboxyl group which may be from glutamyl or aspartyl residues of the enzyme. This car-boxyl group might function as a general acid-base catalyst. A detailed mechanism in terms of the exactamino acid residues involved is proposed.
- 中文關鍵字: malic enzyme; pigeon liver; carboxyl group; mechanism
- 英文關鍵字: --