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Cathepsin D: An intracellular proteinase found in a variety of tissue. It has specificity similar to but narrower than that of pepsin A. The enzyme is involved in catabolism of cartilage and connective tissue. EC 3.4.23.5. (Formerly EC 3.4.4.23).Cathepsins: 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 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.Cathepsin L: A ubiquitously-expressed cysteine protease that plays an enzymatic role in POST-TRANSLATIONAL PROTEIN PROCESSING of proteins within SECRETORY GRANULES.Cathepsin K: A cysteine protease that is highly expressed in OSTEOCLASTS and plays an essential role in BONE RESORPTION as a potent EXTRACELLULAR MATRIX-degrading enzyme.Cathepsin E: An aspartic endopeptidase that is similar in structure to CATHEPSIN D. It is found primarily in the cells of the immune system where it may play a role in processing of CELL SURFACE ANTIGENS.Cathepsin H: An ubiquitously-expressed lysosomal cysteine protease that is involved in protein processing. The enzyme has both endopeptidase and aminopeptidase activities.Cathepsin G: A serine protease found in the azurophil granules of NEUTROPHILS. It has an enzyme specificity similar to that of chymotrypsin C.Pepstatins: N-acylated oligopeptides isolated from culture filtrates of Actinomycetes, which act specifically to inhibit acid proteases such as pepsin and renin.Cathepsin C: A papain-like cysteine protease that has specificity for amino terminal dipeptides. The enzyme plays a role in the activation of several pro-inflammatory serine proteases by removal of their aminoterminal inhibitory dipeptides. Genetic mutations that cause loss of cathepsin C activity in humans are associated with PAPILLON-LEFEVRE DISEASE.Lysosomes: A class of morphologically heterogeneous cytoplasmic particles in animal and plant tissues characterized by their content of hydrolytic enzymes and the structure-linked latency of these enzymes. The intracellular functions of lysosomes depend on their lytic potential. The single unit membrane of the lysosome acts as a barrier between the enzymes enclosed in the lysosome and the external substrate. The activity of the enzymes contained in lysosomes is limited or nil unless the vesicle in which they are enclosed is ruptured. Such rupture is supposed to be under metabolic (hormonal) control. (From Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)Cathepsin F: A lysosomal papain-related cysteine proteinase that is expressed in a broad variety of cell types.Cathepsin Z: A ubiquitously-expressed cysteine peptidase that exhibits carboxypeptidase activity. It is highly expressed in a variety of immune cell types and may play a role in inflammatory processes and immune responses.Cysteine 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.Cathepsin W: A cysteine endopeptidase found in NATURAL KILLER CELLS and CYTOTOXIC T-LYMPHOCYTES. It may have a specific function in the mechanism or regulation of cytolytic activity of immune cells.Endopeptidases: A subclass of PEPTIDE HYDROLASES that catalyze the internal cleavage of PEPTIDES or PROTEINS.Enzyme Precursors: Physiologically inactive substances that can be converted to active enzymes.Mannosephosphates: Phosphoric acid esters of mannose.Cystatins: 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.Protease Inhibitors: Compounds which inhibit or antagonize biosynthesis or actions of proteases (ENDOPEPTIDASES).Cathepsin A: A carboxypeptidase that catalyzes the release of a C-terminal amino acid with a broad specificity. It also plays a role in the LYSOSOMES by protecting BETA-GALACTOSIDASE and NEURAMINIDASE from degradation. It was formerly classified as EC 3.4.12.1 and EC 3.4.21.13.Cysteine Proteinase Inhibitors: Exogenous and endogenous compounds which inhibit CYSTEINE ENDOPEPTIDASES.Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Receptor, IGF Type 2: A receptor that is specific for IGF-II and mannose-6-phosphate. The receptor is a 250-kDa single chain polypeptide which is unrelated in structure to the type 1 IGF receptor (RECEPTOR, IGF TYPE 1) and does not have a tyrosine kinase domain.Aspartic Acid Endopeptidases: A sub-subclass of endopeptidases that depend on an ASPARTIC ACID residue for their activity.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Dipeptides: Peptides composed of two amino acid units.beta-N-Acetylhexosaminidases: A hexosaminidase specific for non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. It acts on GLUCOSIDES; GALACTOSIDES; and several OLIGOSACCHARIDES. Two specific mammalian isoenzymes of beta-N-acetylhexoaminidase are referred to as HEXOSAMINIDASE A and HEXOSAMINIDASE B. Deficiency of the type A isoenzyme causes TAY-SACHS DISEASE, while deficiency of both A and B isozymes causes SANDHOFF DISEASE. The enzyme has also been used as a tumor marker to distinguish between malignant and benign disease.Lysosome-Associated Membrane Glycoproteins: Ubiquitously expressed integral membrane glycoproteins found in the LYSOSOME.DiazomethaneAcid Phosphatase: An enzyme that catalyzes the conversion of an orthophosphoric monoester and water to an alcohol and orthophosphate. EC 3.1.3.2.Acetylglucosaminidase: A beta-N-Acetylhexosaminidase that catalyzes the hydrolysis of terminal, non-reducing 2-acetamido-2-deoxy-beta-glucose residues in chitobiose and higher analogs as well as in glycoproteins. Has been used widely in structural studies on bacterial cell walls and in the study of diseases such as MUCOLIPIDOSIS and various inflammatory disorders of muscle and connective tissue.Serine Endopeptidases: Any member of the group of ENDOPEPTIDASES containing at the active site a serine residue involved in catalysis.Mucolipidoses: A group of inherited metabolic diseases characterized by the accumulation of excessive amounts of acid mucopolysaccharides, sphingolipids, and/or glycolipids in visceral and mesenchymal cells. Abnormal amounts of sphingolipids or glycolipids are present in neural tissue. INTELLECTUAL DISABILITY and skeletal changes, most notably dysostosis multiplex, occur frequently. (From Joynt, Clinical Neurology, 1992, Ch56, pp36-7)Substrate Specificity: A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.Protein Processing, Post-Translational: Any of various enzymatically catalyzed post-translational modifications of PEPTIDES or PROTEINS in the cell of origin. These modifications include carboxylation; HYDROXYLATION; ACETYLATION; PHOSPHORYLATION; METHYLATION; GLYCOSYLATION; ubiquitination; oxidation; proteolysis; and crosslinking and result in changes in molecular weight and electrophoretic motility.Phagosomes: Membrane-bound cytoplasmic vesicles formed by invagination of phagocytized material. They fuse with lysosomes to form phagolysosomes in which the hydrolytic enzymes of the lysosome digest the phagocytized material.Autolysis: The spontaneous disintegration of tissues or cells by the action of their own autogenous enzymes.Endosomes: Cytoplasmic vesicles formed when COATED VESICLES shed their CLATHRIN coat. Endosomes internalize macromolecules bound by receptors on the cell surface.Peptide Hydrolases: Hydrolases that specifically cleave the peptide bonds found in PROTEINS and PEPTIDES. Examples of sub-subclasses for this group include EXOPEPTIDASES and ENDOPEPTIDASES.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 3.4.22.2.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.