title: Purification and characterization of protease III from Escherichia coli.
abstract: An endoproteolytic enzyme of Escherichia coli, designated protease III, has been purified about 9,600-fold to homogeneity with a 6% yield. The purified enzyme consists of a single polypeptide chain of Mr 110,000 and is most active at pH 7.4. Protease III is very sensitive to metal-chelating agents and reducing agents. The EDTA-inactivated enzyme can be reactivated by Zn2+, Co2+ or Mn2+. Protease III is devoid of activity toward aminopeptidase, carboxypeptidase, or esterase substrates but rapidly degrades small proteins. When fragments of beta-galactosidase are used as substrates for protease III, the enzyme preferentially degrades proteins with molecular weights of less than 7,000. Protease III cleaves the oxidized insulin B chain at two sites with an initial rapid cleavage at Tyr-Leu (16-17) and a second slower cut at Phe-Tyr (25-26).
mesh_terms: D002413:Cations, Divalent; D004355:Drug Stability; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008666:Metalloendopeptidases; D008970:Molecular Weight; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D010450:Endopeptidases; D008666:Metalloendopeptidases; C022653:auR protein, Staphylococcus aureus