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Biomedical subjects

A Azzi

Publications and source records attributed to A Azzi.

At least 217 records · Page 12Linked to original sources
PubMed1979

Molecular aspects of cytochrome c oxidase: structure and dynamics.

In the last few years much attention has been dedicated to the elucidation of some of the molecular aspects of cytochrome c oxidase. It has been shown conclusively that the enzyme from several sources (yeast, Neurospora, heart, liver) contains seven different subunits, which are asymmetrically inserted in the membrane. All of these are in contact with the lipid bilayer (except subunits V and VI) and to a greater or lesser extent with the water phase as well (except for subunit I). Subunit II of the enzyme appears to be involved in the formation of the binding site of cytochrome c. The location of the redox groups of the enzyme is still a matter of controversy. Their distance from the cytochrome c heme group is approximately 35 A such that electron tunneling appears to be the only possible mechanism for transporting electrons across such a distance. A proton pump appears to be associated with electron transport and approximately one proton is extruded per electron equivalent reducing oxygen via the enzyme. N,N', dicyclohexylcarbodiimide a well-established inhibitor of H+-translocating ATPases inhibits the proton pump and labels specifically subunit III of the enzyme.

Animals↗
PubMed1979

Cytochrome c oxidase subunits in contact with phospholipids. Hydrophobic photolabeling with azidophospholipids.

The technique of photolabeling of membrane proteins with arylazidophospholipids was applied to cytochrome c oxidase. The "deep" and "shallow" labels employed reacted with all subunits of cytochrome c oxidase except V and VI: Subunits I, III, and VII were heavily labeled, Subunit II was labeled to a lesser extent, and Subunit IV was poorly labeled. Subunit I was labeled more by the deep label and Subunit VII by the shallow one. The other subunits were equally labeled by the two probes. This technique has revealed what subunits of cytochrome c oxidase interact with the lipid and their approximate position in the membrane.

Animals↗
PubMed1979

Limited-turnover studies on proton translocation in reconstituted cytochrome c oxidase-containing vesicles.

We have investigated ferrocytochrome c-induced proton ejection from reconstituted cytochrome c oxidase-containing vesicles using careful control of the number of enzyme turnovers. Ferrocytochrome c caused the appearance of protons at the vesicle exterior, and this could be abolished by using a protonophore. In addition, its decay was dependent on the permeability of the vesicle membranes to protons and the number of turnovers of the oxidase. These observations indicate that the ejection of protons was the result of genuine translocation. The possibility of this translocation occurring via a Mitchellian loop as a result of the presence of a reduced hydrogen carrier contaminating the enzyme was considered and excluded. Proton-translocating activity in this reconstituted system depended critically on the ratio of enzyme to lipid used in the reconstitution process and we propose a rationale to account for this. We conclude that our data provide strong support for the proposal that cytochrome c oxidase acts as a proton pump and that approx. 0.9 H+ is excluded per ferrocytochrome c molecule oxidized.

Binding Sites↗
PubMed1979

Purification of the chloroplast-membrane dicyclohexylcarbodi-imide-binding proteolipid by ion-exchange chromatography.

An efficient, mild and rapid procedure is reported for the separation of the dicyclohexyl-carbodi-imide-binding protein of chloroplast membranes from endogenous lipid components. By the use of ion-exchange chromatography the chloroplast proteolipid can be successfully separated from the major part of chlorophyll and other membrane lipids while being retained in a butan-1-ol milieu.

Carbodiimides↗
PubMed1978

Characterization of the dicyclohexylcarbodiimide-binding protein isolated from chloroplast membranes.

Characterization of a butanol-solubilized protein isolated from chloroplast membranes is reported. The proteolipid, which specifically and covalently binds dicyclohexylcarbodiimide, has an apparent molecular weight of 8,000 in dodecylsulfate electrophoresis. The minimum molecular weight calculated from amino acid analysis data is 7,700. N-Formyl-methionine was determined to be the N-terminal amino acid. Glycine, alanine and leucine were present in elevated amounts, resulting in a polarity of 29%. Cysteine and histidine were lacking. In high-voltage electrophoresis the peptide appeared as a single homogenous spot which migrated, at pH 6.5, with the relative mobility of glycine. At concentrations where dicyclohexylcarbodiimide inhibited ATPase activity maximally (20 nmol per mg membrane protein), 0.17 nmol dicyclohexylcarbodiimide was covalently bound per nmol isolated proteolipid, indicating that one out of six molecules of proteolipid was labeled.

Adenosine Triphosphatases↗
PubMed1978

Interaction of cytochrome c with cytochrome c oxidase. Photoaffinity labeling of beef heart cytochrome c oxidase with arylazido-cytochrome c.

Cytochrome c derivatives labeled with a 3-nitrophenylazido group at lysine 13, at lysine 22, or at both residues have been prepared. The interaction of the cytochrome c derivatives with beef heart cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) in the presence of ultrviolet light results in formation of a covalent complex between cytochrome c and the oxidase. Using the lysine 22 derivative, the polypeptide composition of the oxidase is not modified, nor is its catalytic activity, whereas with the lysine 13 derivative, the gel electrophoretic pattern is altered and the catalytic activity of the complex diminished. The data are consisten with a specfic covalent interaction of the lysine 13 derivative of cytochrome c with the polypeptide of molecular weight 23,700 (Subunit II) of cytochrome c oxidase.

Affinity Labels↗
PubMed1977

Hepatic microsomal dealkylations. Inhibition by a tyrosine-copper (II) complex provided with superoxide dismutase activity.

The effect of a divalent copper-tyrosine complex has been evaluated in rat liver microsome-catalyzed dealkylations. The copper complex, which is provided with superoxide dismutase activity, inhibits at micromolar concentrations aminopyrine, p-nitroanisol, and 7-ethoxycoumarin dealkylations. It has also been found that cumene hydroperoxide-supported p-nitroanisol demethylation, the formation of a 440 nm species, and the formation of superoxide radicals are inhibited by the divalent copper complex. On the other hand, 3-chloroperbenzoic acid has been found to support a copper complex-insensitive 7-ethoxycoumarin dealkylation. Oxygen uptake by rat liver microsomes is also inhibited by the copper complex. The data support the concept that the copper complex acts as a superoxide dismutase at the level of a cytochrome P-450 intermediate species, liganded with superoxide anions.

Aminopyrine N-Demethylase↗
PubMed1977

Production of superoxide anions and hydrogen peroxide in Ehrlich ascites tumour cell nuclei.

Nuclei isolated from Ehrlich-Lettré ascites tumour cells catalyze the co-oxidation of epinephrine to adrenochrome in the presence of NADPH. Adrenochrome formation is sensitive to superoxide dismutase but not to scavengers of hydroxyl radicals or singlet oxygen. Addition of NADPH also initiates the production of hydrogen peroxide. Moreover measurements of superoxide dismutase activity indicate the presence of this enzyme in the ascites cell nuclei, although the sensitivity of adrenochrome formation to externally added superoxide dismutase indicates that the endogenous enzyme is not sufficient for a complete protection from superoxide radicals.

Animals↗