Thiol peptide hydrolases from animal tissues, their structure and function

Data on properties, structure and biological functions of a variety of thiol (cysteine) peptide hydrolases from animal tissues have been summarized. This large group of diverse intracellular enzymes involves both endo- and exopeptidases. Best studied are lysosomal thiol peptide hydrolases: cathepsins B, H and L, the primary structure of which is deciphered. They present a family of homologous proteins, structurally similar to papain. Ca2+-dependent neutral proteinases is another family of related proteins. The biological functions of various thiol peptide hydrolases are considered: their participation in protein turnover, post-translational processing, regulation of unidirectional biological processes and metabolic refolding. Data on endogenous inhibitors of thiol peptide hydrolases and on regulation of enzymic activity are presented.