頁籤選單縮合
題 名 | Chemical Mechanism of the Endogenous Argininosuccinate Lyase Activity of Duck Lens δ2-crystallin |
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作 者 | Wu,Chi-yue; Lee,Hwei-jen; Wu,Shih-hsiung; Chen,Shui-tein; Chiou,Shyh-horng; Chang,Gu-gang; | 書刊名 | 中央研究院生物化學研究所論文集 |
卷 期 | 24 1998[民87.] |
頁 次 | 頁265-272 |
分類號 | 361.19 |
關鍵詞 | Chemical mechanism; The Endogenous argininosuccinate lyase activity; δ2-crystllin; |
語 文 | 英文(English) |
英文摘要 | The endogenous argininosuccinate lyase activity of duck δ2-crystallin was specifically inactivated by the histidine-specific reagent, dieiliyl pyrocarbonate. The protein was protected by L-citrulline or L-arginine from the diethyl pyrocarbonate inactivation. To characterize further the chemical mechanism of the δ 2-crystallin-catalysed reaction, deuterium-labelled argininosuccinate was enzymically synthesized from fumarate and L-arginine with δ 2-crystallin in �� H �� O. The argininosuccinate synthesized contained about 19% of the anhydride form; however, the deuterium was clearly demonstrated to be incorporated snantioselectively. Only the pro-H □ atom at C-9 of the succinate moiety was labelled in the [ �� H]argininosuccinate-9-d synthesized. which indicates an anti-elimination mechanism for the endogenous argininosuccinate lyase activity of δ 2-crystallin. The enzymic activity of duck lens δ 2-crystallin in the pH range 5.5-8.5 was investigated using both protium- and deuterium-labelled argininosuccinate as the substrate. From the log k □ versus pH plot. two molecular pK �f values of 6.18 ± 0.02 and 8.7 ± 0.03 were detected in the δ 2-crystallin-argimnosuccinate binary complex. The Former must be dehydronated and the latter hydronated to achieve an optimum reaction rate. The log k □ /K �o vesus pH plot suggested two molecular pK �f values of 5.96 ± 0.09 and 8.29 ± 0.10 for the free δ 2-crystallin to be involved in the substrate binding. Small kinetic isotope effects of 1.17 ±0.02 and 1.05 ± 0.09 were found for k □ and k □ /K �o respectively. Combining results from labelling and kinetic analysis indicates that the endogenous argininosuccinate lyase activity of duck δ 2-crystallin is compatible with a stepwise ElcB mechanism, the rate-limiting step probably at the C-N bond-cleavage step. |
本系統中英文摘要資訊取自各篇刊載內容。