title: Escherichia coli contains a soluble ATP-dependent protease (Ti) distinct from protease La.
abstract: The energy requirement for protein breakdown in Escherichia coli has generally been attributed to the ATP-dependence of protease La, the lon gene product. We have partially purified another ATP-dependent protease from lon-cells that lack protease La (as shown by immunoblotting). This enzyme hydrolyzes [3H]methyl-casein to acid-soluble products in the presence of ATP and Mg2+. ATP hydrolysis appears necessary for proteolytic activity. Since this enzyme is inhibited by diisopropyl fluorophosphate, it appears to be a serine protease, but it also contains essential thiol residues. We propose to name this enzyme protease Ti. It differs from protease La in nucleotide specificity, inhibitor sensitivity, and subunit composition. On gel filtration, protease Ti has an apparent molecular weight of 370,000. It can be fractionated by phosphocellulose chromatography or by DEAE chromatography into two components with apparent molecular weights of 260,000 and 140,000. When separated, they do not show proteolytic activity. One of these components, by itself, has ATPase activity and is labile in the absence of ATP. The other contains the diisopropyl fluorophosphate-sensitive proteolytic site. These results and the similar findings of Katayama-Fujimura et al. [Katayama-Fujimura, Y., Gottesman, S. & Maurizi, M. R. (1987) J. Biol. Chem. 262, 4477-4485] indicate that E. coli contains two ATP-hydrolyzing proteases, which differ in many biochemical features and probably in their physiological roles.
authors.forename: B J
authors.initials: BJ
authors.lastname: Hwang
authors.forename: W J
authors.initials: WJ
authors.lastname: Park
authors.forename: C H
authors.initials: CH
authors.lastname: Chung
authors.forename: A L
authors.initials: AL
authors.lastname: Goldberg
mesh_terms: D049069:ATP-Dependent Proteases; D000255:Adenosine Triphosphate / Q000378:metabolism; D002364:Caseins / Q000378:metabolism; D010450:Endopeptidases / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D008274:Magnesium / Q000378:metabolism; D008970:Molecular Weight; D009711:Nucleotides / Q000378:metabolism; D049070:Protease La; D012697:Serine Endopeptidases; D013379:Substrate Specificity
chemical_list: D002364:Caseins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D009711:Nucleotides; D000255:Adenosine Triphosphate; D010450:Endopeptidases; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La; D008274:Magnesium