13C-labeled indolequinone-DTPA-Gd conjugate for NMR probing cytochrome:P450 reductase-mediated one-electron reduction

We designed and synthesized a new class of 13C-labeled NMR probe, 13C-IQ-Gd, to monitor one-electron reductions by cytochrome:P450 (CYP450) reductase under hypoxic conditions. 13C-IQ-Gd consisted of a Gd3+-diethylene triamine pentaacetic acid (DTPA) complex unit and an indolequinone (13C-IQ) unit bearing a 13C-labeled methoxy group. The 13C NMR signal of 13C-IQ-Gd was suppressed because of the intramolecular paramagnetic effect of Gd3+, whereas enzymatic reduction mediated by CYP450 reductase under hypoxic conditions yielded an intensed 13C NMR signal due to enzymatic activation of the IQ unit followed by release of the DTPA-Gd unit from 13C-IQ-Gd. This 13C NMR spectral change allowed the monitoring of CYP450 reducatase-mediated one-electron reduction.

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