Figure 2.

Fluorescence imaging of cathepsin activity using quenched activity-based probes (qABPs). A) Mechanism of covalent inhibition of a protease by an acyloxymethyl ketone. B) Activity-dependent labeling of a protease target by a qABP. Covalent modification of the target results in loss of the quenching group, resulting in production of a fluorescently labeled enzyme. C) Optical imaging of tumors in live mice. The red circles indicate the tumor (top) and an area (bottom) used for the measurement of background signal. Adapted from ³⁵, ³⁷.