Mechanistic Study of an Improbable Reaction: Alkene Dehydrogenation by the 12 Acetylenase of Crepis alpina

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• 作者：Darwin W. Reed ; Devin R. Polichuk ; Peter H. Buist ; Stephen J. Ambrose ; Robert J. Sasata ; Christopher K. Savile ; Andrew R. S. Ross ; and Patrick S. Covello
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：September 3, 2003
• 年：2003
• 卷：125
• 期：35
• 页码：10635 - 10640
• 全文大小：86K
• 年卷期：v.125,no.35(September 3, 2003)
• ISSN：1520-5126

文摘

The mechanism by which the fatty acid acetylenase of Crepis alpina catalyzes crepenynic acid((9Z)-octadeca-9-en-12-ynoic acid) production from linoleic acid has been probed through the use of kineticisotope effect (KIE) measurements. This was accomplished by incubating appropriate mixtures ofregiospecifically deuterated isotopomers with a strain of Saccharomyces cerevisiae expressing a functionalacetylenase. LC/MS analysis of crepenynic acid obtained in these experiments showed that the oxidationof linoleate occurs in two discrete steps, since the cleavage of the C12-H bond is very sensitive to isotopicsubstitution (k_H/k_D = 14.6 ± 3.0) while a minimal isotope effect (k_H/k_D = 1.25 ± 0.08) was observed for theC13-H bond breaking step. These data suggest that crepenynic acid is produced via initial H-atomabstraction at C12 of a linoleoyl substrate. The relationship between the mechanism of enzymaticacetylenation and epoxidation is discussed.