Epoxysuccinyl peptide‐derived affinity labels for cathepsin B

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Abstract
Extracellular cysteine proteases, in particular cathepsin B, have been implicated in a variety of pathological processes. Selectively targeting labels of this enzyme are important tools to gain more detailed understanding of its specific roles. Starting from our recently developed irreversible epoxysuccinyl‐based inhibitor (R‐Gly‐Gly‐Leu‐(2S,3S)‐tEps‐Leu‐Pro‐OH, R=OMe), we have synthesized two affinity labels, R=NH‐(CH2)6‐NH‐rhodamine B and R=NH‐(CH2)6‐NH‐biotin. Using MCF‐7 cells, the labeled inhibitors were shown to be virtually non‐cell‐permeant. Moreover, affinity blot analysis with the biotinylated inhibitor allowed a highly sensitive and selective non‐radioactive detection of active cathepsin B.