Ubiquitin carboxyl-terminal hydrolases (EC 220.127.116.11) (UCH) (deubiquitinating
enzymes) [1,2] are thiol proteases that recognize and hydrolyze the peptide
bond at the C-terminal glycine of ubiquitin. These enzymes are involved in the
processing of poly-ubiquitin precursors as well as that of ubiquinated
There are two distinct families of UCH. The first class consist of enzymes of
about 25 Kd and is currently represented by:
Mammalian isozymes L1, L3 and L5.
One of the active site residues of class-I UCH  is a cysteine. We derived
a signature pattern from the region around that residue.
These proteins belong to family C12 in the classification of peptidases
December 2001 / Text revised.
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