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They proposed a mechanism of catalysis that involves nucleophilic attack of the active site cysteine that is aided by stabilization of the tetrahedral intermediate by an oxyanion hole formed from the backbone amides of Cys159 and Ala155 (AbPncA numbering). Asp16 was proposed to deprotonate Cys159 to initiate catalysis and to donate a proton to aid the release of NH3 during the tetrahedral intermediate collapse to form the thioester acyl intermediate. Water is then activated by proton abstraction by Asp16 for nucleophilic attack on the covalent acyl-enzyme intermediate to yield a thiolate and nicotinic acid. Transfer of a proton from Asp16 to the active site cysteine completes the catalytic cycle. ÆäÖÐÁ½¾äÖÐÓÐÁ½¸öby£¬ÓÐЩŪ²»Ã÷°×£¬Õâ¾ä×ÓÊÇʲôÒâ˼£¬Çó·ÖÎö£¬×îºÃÄܹýдÇå³þ¾ä×ӽṹ¡£Ð»Ð»ÁË |
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£¨1£©They proposed a mechanism of catalysis that involves nucleophilic attack of the active site cysteine ¡¾that is aided by stabilization of the tetrahedral intermediate¡¿ ¡¾ formed by an oxyanion hole formed from the backbone amides of Cys159 and Ala155 (AbPncA numbering)¡¿. ÓÐÈËÌá³öÁËÒ»¸ö»îÐÔλµãcysµÄÇ׺˹¥»÷µÄ´ß»¯»úÀí£¬ÓÉËÄÃæÌåÖмäÎïµÄÎȶ¨À´¸¨ÖúÇ¿»¯£¬Õâ¸öËÄÃæÌåÖмäÎï¾ÍÊÇCys159 and Ala155 ÖмäµÄ¹Ç¼ÜÐγɵÄÑõÀë×ÓѨ¶øÀ´µÄ¡£ £¨2£© Water is then activated by proton abstraction ¡¾by Asp16 for nucleophilic attack on the covalent acyl-enzyme intermediate¡¿ to yield a thiolate and nicotinic acid. ÔÚAsp16É϶Թ²¼Ûõ£»ùøÖмäÎï½øÐÐÇ׺˹¥»÷Ëù²úÉúµÄÖÊ×ÓÎüÊÕÄܹ»¼¤»îË®£¬´Ó¶ø²úÉúÁò´¼ÑκÍÑÌËá |
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3Â¥2012-09-03 14:00:59
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4Â¥2012-09-03 15:59:17
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- Ìû×Ó: 273
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