Ubiquitin-protein hydrolase involved both in the processing of ubiquitin precursors and of ubiquitinated proteins (Probable). This enzyme is a thiol protease that recognizes and hydrolyzes a peptide bond at the C-terminal glycine of ubiquitin (PubMed:9774100, PubMed:8639624, PubMed:12408865, PubMed:23359680). Also binds to free monoubiquitin and may prevent its degradation in lysosomes (By similarity). The homodimer may have ATP-independent ubiquitin ligase activity (PubMed:12408865). Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Monomer. Homodimer. Interacts with SNCA (By similarity). Interacts with COPS5. About 30% of total UCHL1 is associated with membranes in brain. Found in neuronal cell bodies and processes throughout the neocortex (at protein level). Expressed in neurons and cells of the diffuse neuroendocrine system and their tumors. Weakly expressed in ovary. Down-regulated in brains from Parkinson disease and Alzheimer disease patients. O-glycosylated. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Oxidation of Met-1, Met-6, Met-12, Met-124 and Met-179 to methionine sulfoxide, and oxidation of Cys-220 to cysteine sulfonic acid have been observed in brains from Alzheimer disease (AD) and Parkinson disease (PD) patients. In AD, UCHL1 was found to be associated with neurofibrillary tangles. In contrast to UCHL3, does not hydrolyze a peptide bond at the C-terminal glycine of NEDD8. Belongs to the peptidase C12 family. PubMed:9774100 reports the association of mutation Ile93Met with Parkinson disease. However, according to PubMed:16450370 this association is uncertain and UCHL1 is not a susceptibility gene for Parkinson disease. The oxidation forms of Met-1, Met-6, Met-12, Met-124, Met-179 and Cys-220 are subject of controversy and could be the artifactual results of sample handling. The homodimer may have ATP-independent ubiquitin ligase activity (PubMed:12408865). However, in another study, UCHL1 was shown to lack ubiquitin ligase activity (PubMed:23359680). Truncated N-terminus. Ubiquitin carboxy-terminal hydrolase L1 entry