Papain: A proteolytic enzyme obtained from Carica papaya. It is also the name used for a purified mixture of papain and CHYMOPAPAIN that is used as a topical enzymatic debriding agent. EC A sulfhydryl proteinase with cysteine at the active site from ficus latex. Preferential cleavage is at tyrosine and phenylalanine residues. EC A homologous group of endogenous CYSTEINE PROTEINASE INHIBITORS. The cystatins inhibit most CYSTEINE ENDOPEPTIDASES such as PAPAIN, and other peptidases which have a sulfhydryl group at the active site.Chymopapain: A cysteine endopeptidase isolated from papaya latex. Preferential cleavage at glutamic and aspartic acid residues. EC Endopeptidases: ENDOPEPTIDASES which have a cysteine involved in the catalytic process. This group of enzymes is inactivated by CYSTEINE PROTEINASE INHIBITORS such as CYSTATINS and SULFHYDRYL REAGENTS.Bromelains: Protein-digesting and milk-clotting enzymes found in PINEAPPLE fruit juice and stem tissue. Enzymes from the two sources are distinguished as fruit bromelain and stem bromelain. This enzyme was formerly listed as EC A group of lysosomal proteinases or endopeptidases found in aqueous extracts of a variety of animal tissues. They function optimally within an acidic pH range. The cathepsins occur as a variety of enzyme subtypes including SERINE PROTEASES; ASPARTIC PROTEINASES; and CYSTEINE PROTEASES.Cathepsin H: An ubiquitously-expressed lysosomal cysteine protease that is involved in protein processing. The enzyme has both endopeptidase and aminopeptidase activities.Cathepsin L: A ubiquitously-expressed cysteine protease that plays an enzymatic role in POST-TRANSLATIONAL PROTEIN PROCESSING of proteins within SECRETORY GRANULES.Cathepsin B: A lysosomal cysteine proteinase with a specificity similar to that of PAPAIN. The enzyme is present in a variety of tissues and is important in many physiological and pathological processes. In pathology, cathepsin B has been found to be involved in DEMYELINATION; EMPHYSEMA; RHEUMATOID ARTHRITIS, and NEOPLASM INVASIVENESS.2,2'-Dipyridyl: A reagent used for the determination of iron.Cysteine Proteinase Inhibitors: Exogenous and endogenous compounds which inhibit CYSTEINE ENDOPEPTIDASES.Endopeptidases: A subclass of PEPTIDE HYDROLASES that catalyze the internal cleavage of PEPTIDES or PROTEINS.Cystatin B: An intracellular cystatin subtype that is found in a broad variety of cell types. It is a cytosolic enzyme inhibitor that protects the cell against the proteolytic action of lysosomal enzymes such as CATHEPSINS.Kinetics: The rate dynamics in chemical or physical systems.