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. Author manuscript; available in PMC: 2015 Aug 4.
Published in final edited form as: Chemistry. 2014 Jul 2;20(32):9840–9850. doi: 10.1002/chem.201402474

Figure 4.

Figure 4

Detecting enzyme activities with CEST MR methods. (A): The cleavage of a peptidyl ligand of a CEST agent, DEVD-amido-(Tm-DOTA), by caspase-3 converts an amide to an amine. (B): The conjugation a CEST agent, Tm-DO3A-cadaverine, to a protein’s glutamine side chain by TGase converts an amine to an amide. (C): The CEST spectra of DEVD-amido-(Tm-DOTA) before (black) and after (gray) incubation with caspase-3 showed a decrease in CEST at μ̵11 ppm and the appearance of CEST at +8 ppm. This appearance of CEST was further confirmed by deconvoluting the CEST spectrum of the product (dashed line), which confirmed the detection of caspase-3 enzyme activity. (D): The CEST spectra of a mixture of albumin, Tm-DO3A-cadaverine and L-glutathione before (black) and after (gray) incubation with TGase showed a decrease in CEST at +4.6 ppm and the appearance of CEST at −9.2 ppm, which demonstrated detection of TGase activity. Reproduced with permission from (55) and (53).