title: Role of nuclear-encoded subunits of mitochondrial cytochrome c oxidase in proton pumping revealed by limited enzymatic proteolysis.
abstract: The role of supernumerary subunits of bovine heart cytochrome c oxidase has been investigated by examining the effect on the enzymatic activity of limited proteolysis by chymotrypsin, thermolysin, and trypsin. All three proteases, when added to the soluble oxidase, digested subunits III, VIa, and VIb and caused inhibition of electron flow in the oxidase. In addition, trypsin and thermolysin also digested subunit IV. Trypsin cleaved off an N-terminal segment of seven residues; thermolysin cleaved only the first four residues at the N-terminus of subunit IV. Digestion of the soluble oxidase by trypsin but not by thermolysin caused decoupling of redox-linked proton pumping in the oxidase. It is concluded that the sequence V5-V6-K7 of the hydrophilic N-terminus of subunit IV, which protrudes out of the matrix side of the mitochondrial membrane, mediates the access of protons into the transmembrane proton translocating pathway in the oxidase.
authors.affiliation: Institute of Medical Biochemistry and Chemistry, University of Bari, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Capitanio
authors.forename: R
authors.initials: R
authors.lastname: Peccarisi
authors.forename: G
authors.initials: G
authors.lastname: Capitanio
authors.forename: G
authors.initials: G
authors.lastname: Villani
authors.forename: E
authors.initials: E
authors.lastname: De Nitto
authors.forename: S
authors.initials: S
authors.lastname: Scacco
authors.forename: S
authors.initials: S
authors.lastname: Papa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism*; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D017494:Proton Pumps / Q000502:physiology*; D013329:Structure-Activity Relationship; D013820:Thermolysin / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D017494:Proton Pumps; D003576:Electron Transport Complex IV; D010450:Endopeptidases; D002918:Chymotrypsin; D014357:Trypsin; D013820:Thermolysin