The ultimate goal of proteomics is to characterize the function of all proteins in parallel and in the most physiologically relevant settings possible. A step toward this goal has been the introduction of activity-based proteomics. The simultaneous detection of individual protein activities can be facilitated directly in the proteome using specific activity-based probes consisting of a recognition site targeting a certain enzyme species, a properly positioned reactive site which forms a covalent bond with the target and a reporter tag for visualization and/or purification of the covalently bound target. As properties like polarity, size, charge, structure, and chemical reactivity of the reporter tag have a large impact on the reactivity of the probes toward the target enzymes probes suitable for reporter tagging after the enzyme-activity probe-binding event were designed. These probes resemble the natural substrates more closely and are small and hydrophobic enough to cross the membrane of living cells. Here the methodology for detection of lipolytic activities in intact living cells, including synthesis of probe and reporter, labeling procedure, and detection of target enzymes is described.
