UCHL1 also known as PGP9.5 is a member of the peptidase C12 family. UCHL1 plays a crucial role in the ubiquitin-proteasome pathway by hydrolyzing small C-terminal adducts of ubiquitin to release free ubiquitin monomers, which are essential for protein degradation and cellular regulation. UCHL1 is predominantly expressed in neurons and cells of the diffuse neuroendocrine system, with significant localization in brain regions such as the substantia nigra, where UCHL1 constitutes 1-2% of total soluble brain protein. UCHL1′s presence in Lewy bodies highlights UCHL1′s potential involvement in neurodegenerative diseases, particularly Parkinson′s disease, making UCHL1 a valuable target for research.