Pepstatin

[1] It was originally isolated from cultures of various species of Actinomyces[1] due to its ability to inhibit pepsin at picomolar concentrations.

Pepstatin A suppresses receptor activator of NF-κB ligand (RANKL)–induced osteoclast differentiation.

Furthermore, pepstatin A decreased the expression of nuclear factor of activated T cells c1 (NFATc1).

These results suggest that pepstatin A suppresses the differentiation of osteoclasts through the blockade of ERK signaling and the inhibition of NFATc1 expression.

[citation needed] Pepstatin is practically insoluble in water, chloroform, ether, and benzene, however it can be dissolved in methanol, ethanol, and DMSO with acetic acid,[3] to between 1 and 5 mg/ml.

Structure of pepstatin in the binding pocket of pepsin. Hydrogen bonds between binding pocket residues and pepstatin are highlighted. Rendered from PDB 1PSO.