PGP9.5/Ubiquitin carboxy-terminal hydrolase L1 is a deubiquitinating enzyme that hydrolyzes small C-terminal adducts of ubiquitin to generate the ubiquitin monomer. It is expressed in neurons, in cells of the diffuse neuroendocrine system and their tumors; it has been subsequently documented in distal renal tubular epithelium, spermatogonia, Leydig cells, oocytes, melanocytes, prostatic secretory epithelium, ejaculatory duct cells, epididymis, mammary epithelial cells, Merkel cells, and dermal fibroblasts.

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