UCH-L1 (ubiquitin carboxy-terminal hydrolases L1) is a member of the carboxyl-terminal ubiquitin hydrolase family, naturally, that there is hydrolase activity, however, and that there is ligase acitivity, which is different from the other members of UCHs. UCH-L1 hydrolase activity could keep the pool of free ubiquitin and compromise the ubiquitin-dependent degradation pathway, while UCH-L1 dimerizational-dependent, ubiquityl ligase activity could produce undegradable, K63-linked polyubiquitin chains that could inhibit proteasomal activity. Therefore, UCH-L1 is involved in the more diverse physiological activities, including neuron formation, gonadal development and fertilization. Mutation of UCH-L1 is linked to the neurodegenerative diseases, such as Parkinson's disease. Moreover, abnormal expression of UCH-L1 is response to carcinogenesis in many tissue such as thyroid lung.