Amide proton transfer of carnosine in aqueous solution studied in vitro by WEX and CEST experiments

NMR Biomed. 2015 Sep;28(9):1097-103. doi: 10.1002/nbm.3343. Epub 2015 Jul 14.

Abstract

Amide protons of peptide bonds induce an important chemical exchange saturation transfer (CEST) contrast in vivo. As a simple in vitro model for a peptide amide proton CEST effect, we suggest herein the dipeptide carnosine. We show that the metabolite carnosine creates a CEST effect and we study the properties of the exchange of the amide proton (-NH) of the carnosine peptide bond (NHCPB) in model solutions for a pH range from 6 to 8.3 and a temperature range from T = 5 °C to 43 °C by means of CEST and water exchange spectroscopy (WEX) experiments on a 3 T whole-body MR tomograph. The dependence of the NHCPB chemical exchange rate k(sw) on pH and temperature T was determined using WEX. For physiological conditions (T = 37 °C, pH = 7.10) we obtained k(sw) = (47.07 ± 7.90)/s. With similar chemical shift and exchange properties to amide protons in vivo, carnosine forms a simple model system for optimization of CEST pulse sequences in vitro. The potential for direct detection of the metabolite carnosine in vivo is discussed.

Keywords: APT; CEST; WEX; carnosine; chemical exchange; pH; peptide bond; proton transfer.

MeSH terms

  • Amides
  • Carnosine / chemistry*
  • Hydrogen-Ion Concentration
  • Magnetic Resonance Spectroscopy / methods*
  • Protons
  • Solutions
  • Temperature

Substances

  • Amides
  • Protons
  • Solutions
  • Carnosine