Elected Academician of Academia Sinica

American Academy of Microbiology Fellow

American Chemical Society Fellow

The University of Texas at Austin

时  间：2017年05月16日（星期二） 13:15-14:20

Abstract/报告摘要：

SpnF is a polyketide tailoring enzyme in the biosynthetic pathway of the insecticide spinosyn A produced by Saccaropolyspora spinosa. SpnF was the first reported enzyme that specifically catalyzes a [4+2]-cycloaddition without introducing any other changes to its substrate. The same cycloaddition also takes place nonenzymatically, but at a much reduced rate. If the reaction catalyzed by SpnF is a concerted process with a single pericyclic transition state, then SpnF would be the first example of a naturally selected Diels-Alderase. In order to investigate this possibility, α-secondary deuterium kinetic isotope effects were measured at both points of rehybridization in the diene during both the nonenzymatic and SpnF-catalyzed [4+2]-cycloaddition reactions. This was accomplished using regiospecifically deuterated substrates and electrospray ionization, time-of-flight mass spectrometry to follow changes in deuterium enrichment of the substrate as the reaction progressed. The presentation will describe the methodology and theory underlying the measurement of these KIEs, address the key challenges regarding these measurements and offer a mechanistic discussion of their implications for understanding the SpnF catalyzed [4+2]-cycloaddition.