(S)-Styryl-伪-alanine Used To Probe the Intermolecular Mechanism of an Intramolecular MIO-Aminomutase

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• 作者：Udayanga Wanninayake ; Yvonne DePorre ; Mark Ondari ; Kevin D. Walker
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：November 22, 2011
• 年：2011
• 卷：50
• 期：46
• 页码：10082-10090
• 全文大小：431K
• 年卷期：v.50,no.46(November 22, 2011)
• ISSN：1520-4995

文摘

A Taxus canadensis phenylalanine aminomutase (TcPAM) catalyzes the isomerization of (S)-伪- to (R)-尾-phenylalanine, making (E)-cinnamate (10%) as a byproduct at steady state. A currently accepted mechanism for TcPAM suggests that the amino group is transferred from the substrate to a prosthetic group comprised of an amino acid triad in the active site and then principally rebinds to the carbon skeleton of the cinnamate intermediate to complete the 伪鈥撐?isomerization. In contrast, when (S)-styryl-伪-alanine is used as a substrate, TcPAM produces (2E,4E)-styrylacrylate as the major product (>99%) and (R)-styryl-尾-alanine (<1%). Comparison of the rates of conversion of the natural substrate (S)-伪-phenylalanine and (S)-styryl-伪-alanine to their corresponding products (k_cat values of 0.053 卤 0.001 and 0.082 卤 0.002 s^鈥?, respectively) catalyzed by TcPAM suggests that the amino group resides in the active site longer than styrylacrylate. To demonstrate this principle, inhibition constants (K_I) for selected acrylates ranging from 0.6 to 106 渭M were obtained, and each had a lower K_I compared to that of (2E,4E)-styrylacrylate (337 卤 12 渭M). Evaluation of the inhibition constants and the rates at which both the 伪/尾-amino acids (between 7 and 80% yield) and styrylacrylate were made from a corresponding arylacrylate and styryl-伪-alanine, respectively, by TcPAM catalysis revealed that the reaction progress was largely dependent on the K_I of the acrylate. Bicyclic amino donor substrates also transferred their amino groups to an arylacrylate, demonstrating for the first time that ring-fused amino acids are productive substrates in the TcPAM-catalyzed reaction.