Quantification of rate constants for successive enzymatic reactions with DNP hyperpolarized MR

• Published in: NMR in biomedicine Vol. 27; no. 6; pp. 656 - 662
• Main Authors: Allouche-Arnon, Hyla, Hovav, Yonatan, Friesen-Waldner, Lanette, Sosna, Jacob, Moshe Gomori, J., Vega, Shimon, Katz-Brull, Rachel
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-06-2014; Wiley Subscription Services, Inc
• Subjects: 13C; Alcohol Oxidoreductases - metabolism; aldehyde; Betaine - metabolism; choline; first order; hyperpolarization; Kinetics; Magnetic Resonance Spectroscopy - methods; rate constant; first order; 13C; choline; aldehyde; hyperpolarization; kinetics; rate constant; T1
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.3102

A kinetic model is provided to obtain reaction rate constants in successive enzymatic reactions that are monitored using NMR spectroscopy and hyperpolarized substrates. The model was applied for simulation and analysis of the successive oxidation of choline to betaine aldehyde, and further to betaine, by the enzyme choline oxidase. This enzymatic reaction was investigated under two different sets of conditions: two different choline molecular probes were used, [1,1,2,2‐D4, 1‐13C]choline chloride and [1,1,2,2‐D4, 2‐13C]choline chloride, in different MR systems (clinical scanner and high‐resolution spectrometer), as well as in different reactors and reaction volumes (4.8 and 0.7 mL). The kinetic analysis according to the model yielded similar results in both set‐ups, supporting the robustness of the model. This was achieved despite the complex and negating influences of reaction kinetics and polarization decay, and in the presence of uncontrolled mixing characteristics, which may introduce uncertainties in both effective timing and effective pulses. The ability to quantify rate constants using hyperpolarized MR in the first seconds of consecutive enzyme activity is important for further development of the utilization of dynamic nuclear polarization‐MR for biological determinations. Copyright © 2014 John Wiley & Sons, Ltd.
A kinetic model is provided to obtain reaction rate constants in successive enzymatic reactions monitored using NMR spectroscopy and hyperpolarized substrates. The model was applied for the simulation and analysis of the successive oxidation of choline to betaine aldehyde hydrate and, further, to betaine by the enzyme choline oxidase. Reactions were monitored using two hyperpolarized choline molecular probes, [1,1,2,2‐D4, 1‐13C]choline chloride and [1,1,2,2‐D4, 2‐13C]choline chloride, in both a clinical scanner and a high‐resolution spectrometer.