Journal of the American Chemical Society
Communication
therefore interested to know whether the new hydrogen in 1-
octadecene was derived from the solvent or some other source.
To avoid complications arising from exchange of the aldehyde
proton during the deuterium labeling experiment, we prepared
6 in which the α-carbon was dideuterated (see the SI). When
dideuterated 6 was reacted with cAD in deuterated buffer, the
predominant molecular ion for 1-octadecene appeared at m/z
255.3 (Figure S21), corresponding to trideuterated 1-
octadecene. This is consistent with the proton coming from
the solvent or a solvent-exchangeable group on the enzyme.
However, a less abundant but still significant peak at m/z
254.3 was also observed, corresponding to dideuterated 1-
octadecene (Figure S21). This suggests that some hydrogen
may derive from a nonexchangeable position on the protein.
(Some protium may also come from the 1−2% protium
remaining in the buffer, but it seems unlikely that this would
account for all of the dideuterated product). Abstraction of
hydrogen from a nonacidic side chain by the alkyl radical
derived from 6 would certainly be energetically feasible. Such
oxidative damage might plausibly result in inactivation of the
enzyme. This may provide an alternative pathway for the
inactivation of cAD by 6 that does not involve in the formation
of a covalent adduct between the protein and the substrate
(Scheme 4, pathway III).
National Science Foundation (CHE 1152055), and the
National Institutes of Health (GM 093088) to E.N.G.M.
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Corresponding Author
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Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We thank Dr. V. Basrur (University of Michigan Proteomic
Facility) for performing MS analyses and advice on the
interpretation of MS data, Dr. Bruce Palfey for advice on kinetic
analysis of octadecene formation, and Dr. Benjamin C. Buer for
assistance with MALDI experiments. This work was supported
in part by grants from the European Union (FP-7 256808), the
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dx.doi.org/10.1021/ja3115949 | J. Am. Chem. Soc. 2013, 135, 5234−5237