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PubMed1990

Respiratory control and ADP:O coupling ratios of isolated chick heart mitochondria.

Heart mitochondria isolated from 14- to 21-day-old chicks are highly coupled and often have respiratory control ratio (RCR) values exceeding 100. This paper presents data from a study of some of the properties of these mitochondria. The studies show that: (a) The ADP:O ratios and the state 4 rates of respiration are highly dependent upon the concentration of mitochondria at which these parameters are measured. (b) The mitochondrial isolate is contaminated with at least two divalent cation-stimulated ATPase, of which one is the F1F0-ATPase of broken mitochondria. (c) The oligomycin-sensitive component of state 4 respiration is completely inhibited by ethylene glycol bis(beta-amino-ethylether) N,N'-tetraacetic acid (EGTA). This inhibition is biphasic and attributable to the differential affinity of EGTA for Ca(II) and Mg(II). (d) Ca(II) and Mg(II) stimulate state 4 respiration, thereby depressing RCR values. These cations also decrease ADP:O ratios from greater than or equal to 3.25 to 3.0 for some NAD-linked substrates. (e) Uncoupled (i.e., oligomycin-insensitive) state 4 respiration can be abolished by treating the mitochondria with Nagarse and by preincubating mitochondria with exogenous substrate. (f) The ADP:O ratios obtained when these heart mitochondria oxidize pyruvate/malate, alpha-ketoglutarate, and beta-hydroxybutyrate are fractional and significantly greater than 3.0.

3-Hydroxybutyric Acid↗
PubMed1992

Role of the amino terminal region of the epsilon subunit of Escherichia coli H(+)-ATPase (F0F1).

Escherichia coli strain KF148(SD-) defective in translation of the uncC gene for the epsilon subunit of H(+)-ATPase could not support growth by oxidative phosphorylation due to lack of F1 binding to Fo (M. Kuki, T. Noumi, M. Maeda, A. Amemura, and M. Futai, 1988, J. Biol. Chem. 263, 17, 437-17, 442). Mutant uncC genes for epsilon subunits lacking different lengths from the amino terminus were constructed and introduced into strain KF148(SD-). F1 with an epsilon subunit lacking the 15 amino-terminal residues could bind to F0 in a functionally competent manner, indicating that these amino acid residues are not absolutely necessary for formation of a functional enzyme. However, mutant F1 in which the epsilon subunit lacked 16 amino-terminal residues showed defective coupling between ATP hydrolysis (synthesis) and H(+)-translocation, although the mutant F1 showed partial binding to Fo. These findings suggest that the epsilon subunit is essential for binding of F1 to F0 and for normal H(+)-translocation. Previously, Kuki et al. (cited above) reported that 60 residues were not necessary for a functional enzyme. However, the mutant with an epsilon subunit lacking 15 residues from the amino terminus and 4 residues from the carboxyl terminus was defective in oxidative phosphorylation, suggesting that both terminal regions affect the conformation of the region essential for a functional enzyme.

Amino Acid Sequence↗
PubMed1976

Energization of mitochondrial inner membranes caused by L-malate.

It was found that 0.06 mug antimycin A/mg mitochondrial protein, an amount sufficient to inhibit electron transfer between cytochromes b and c1 completely, fully reversed the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria. The effect of L-malate on cytochrome a was insensitive to oligomycin, but all the uncouplers and detergents tested reversed the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria. It was also found that addition of L-malate to anaerobic mitochondria, like addition of ATP, decreased the fluorescence of 1-anilinonaphthalene-8-sulphonate, and that subsequent addition of uncouplers reversed this effect. The effect of L-malate on the fluorescence of the dye was insensitive to oligomycin. The present findings suggest that addition of L-malate may cause energization of the mitochondrial inner membranes and that the oxidation of cytochrome a caused by L-malate in anaerobic mitochondria may result from an L-malate-induced, energy-linked reversal of electron transfer in site II.

Adenosine Triphosphate↗
PubMed1978

The use of aurovertin to determine the F1 content of submitochondrial particles and the ATPase complex.

(1) The concentration of aurovertin-binding sites calculated from fluorimetric titrations of submitochondrial particles is equal to the F1 concentration, calculated from the concentration of F1-binding sites in stripped particles. (2) Direct binding experiments show that the fluorescence enhancement of aurovertin bound to submitochondrial particles and the isolated ATPase complex is less (or absent) at higher concentrations than at lower concentrations. The binding data can be described by 'specific' and 'non-specific' binding. The concentration of the 'specific' sites is twice that derived from fluorimetric titrations. (3) After dissociation of the bound F1 with LiCl, fluorimetric titrations with aurovertin yield linear Scatchard plots. The fluorescence enhancement and KD are equal to those of the beta-subunit-aurovertin complex. The concentration of beta-subunits is double the concentration of F1. (4) It is concluded that both for submitochondrial particles and the isolated ATPase complex the most reliable and simple way to determine the F1 content is to dissociate the F1 with LiCl, spin down the insoluble material and titrate the supernatant (containing free beta-subunit) with aurovertin.

Adenosine Triphosphatases↗
PubMed1979

Stabilization of rat liver mitochondrial F1-adenosine triphosphatase during chloroform-induced solubilization.

1. Isolation of ATPase from rat liver submitochondrial particles by chloroform treatment requires the presence of ATP or ADP during enzyme solubilization. In the absence of adenine nucleotides the enzyme activity is very low although all protein components of F1-ATPase are released. The low concentrations of ATP or ADP required (5 microM) indicate that the high affinity nucleotide-binding sites are involved in enzyme stabilization. Other nucleotides tested (ITP, GTP, UTP, CTP) were found to be less effective. 2. Polyacrylamide gel electrophoresis and immunodiffusion in agar plates revealed that in the absence of adenine nucleotides a fraction of F1-ATPase released by chloroform treatment is split into fragments. The part of the dissociated enzyme molecule has a molecular weight identical with that of a beta-subunit of F1-ATPase. 3. Dissociation of the F1-ATPase molecule could also be prevented by aurovertin. 4. Crude F1-ATPase solubilized by chloroform treatment can be further purified by Sepharose 6B gel filtration. Specific ATPase activity of the purified enzyme was 90 mumol Pi/min per mg protein and the enzyme was composed of five protein subunits (alpha, beta, gamma, delta, epsilon) with molecular weights 58 000, 55 000, 28 000, 13 000 and 8000, respectively. 5. Chloroform-released F1-ATPase from rat liver mitochondria displayed immunochemical cross-reactivity with that isolated from beef heart mitochondria.

Adenosine Triphosphatases↗