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Based on the short time scale in which these signals were detectable
and the proposed action mechanism of choline oxidase, we speculate
that these signals represent the enzyme–product complexes that were
formed before the release of [D3, 13C]BAH and/or [D2, 13C]Bet.
The characterization of enzyme kinetics is an important tool in
the exploration of enzymatic mechanisms and activities. Here we
focused on a metabolic pathway which involves the oxidation of
choline to betaine aldehyde and then to betaine and showed the
feasibility of monitoring this enzymatic reaction at a high temporal
resolution (1 s) using hyperpolarized MR. To the best of our knowl-
edge, this is the first demonstration of an aldehyde intermediate in a
hyperpolarized state. Thus, this finding opens the way for further
direct investigation and characterization of these important groups
of enzymes – aldehyde synthesizing enzymes and aldehyde dehy-
drogenases. Because the DNP hyperpolarized magnetic resonance
technology has already proven useful for in vivo investigations,20 it is
likely that the investigation of aldehyde metabolism could also be
carried out in vivo, pending an appropriate model system.
Fig. 3 Time course of a [D4, 13C]Cho oxidation reaction as observed by hyper-
polarized 13C-NMR spectroscopy. The data shown here were obtained from the
experiment shown in Fig. 2. The [D4, 13C]Cho signal intensity was reduced 5 fold
for the purpose of presentation.
The authors thank Mathilde Lerche and Magnus Karlsson of
Albeda Research Laboratory in Copenhagen, Denmark for
performing the hyperpolarized experiments and the Editor
and the reviewers for insightful suggestions. This work was
partially funded by the Israel Science Foundation (Grant No.
284/10 to RKB) and BrainWatch Ltd.
Notes and references
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7078 Chem. Commun., 2013, 49, 7076--7078
This journal is The Royal Society of Chemistry 2013