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an enzyme of the class of hydrolases. Endo-peptidases catalyze the decomposition of internal peptide bonds in proteins and peptides. The speed of hydrolysis of a given peptide bond by different endopeptidases depends on the substrate specificity of the enzyme and the spatial accessibility of the given peptide bond, especially if the substrate is a native, not denatured, protein. It does not depend on the size of the molecules of the substrate, that is, the length of the polypeptide chain. The substrate specificity of an endopeptidase consists in the ability of a given enzyme to hydrolyze the peptide bonds between certain amino acid residues with the greatest speed. For example, chy-motrypsin very rapidly hydrolyzes peptide bonds together with aromatic amino acids; trypsin does the same with diamino acids. Endopeptidases are classified as extracellular or intracellular (tissular). Extracellular endopeptidases are secreted into the digestive cavity of animals (for example, enterokinase) or simply into the external environment (the exo-enzymes of bacteria).
The use of endopeptidases in determining the primary structure of proteins is based on their properties.