Interactions of beef heart mitochondrial adenosine triphosphatase and aurovertin.

Aurovertin forms a complex with soluble beef heart mitochondrial ATPase (F₁) while exhibiting a biphasic fluorence enhancement. The effect of substrate, activators and inhibitors of F₁¹ of the fluorescence of the aurovertin-F₁ complex is reported. The aurovertin-F₁ complex can exist in two different states, one showing low fluorescence and the other with high fluorescence. Transition into the low fluorescence state is induced by various nucleoside triphosphates (ATP ± Mg²⁺, ITP ± Mg²⁺, GIP + Gg²⁺, and AMP-P(NH)P ± Mg²⁺). The rate and extent of fluorescence decrease caused by nucleotide addition (except that caused by ATP) is dependent on the presence of added Mg²⁺. The inhibitors of ATPase activity (AMP-P(NH)P, GMP-P(NH)P and EDTA) at concentrations that inhibit hydrolysis of ATP did not prevent the ATP induced decrease of aurovertin fluorescence. EDTA at high concentration (>0.4 mM) enhanced the effect of ADP.The complex of aurovertin with F₁ that had previously been treated with butanedione loses sensitivity to ATP. Addition of ADP to the system containing butanedione-treated enzyme caused a 2-fold greater enhancement of fluorescence than the addition of ADP to the control system. In contrast to the butanedione-treated enzyme, the complex of aurovertin with F₁ previously treated at pH 5.6 loses sensitivity to ADP. Addition of ATP to this system lowered the fluorescence as in the system containing native enzyme.On the basis of the analyses of the aurovertin fluorescence changes and hydrolytic activity of F₁, the existence of several types of ligand binding sties with varying degrees of specificity are proposed. It is further proposed that these sites are important in control of the conformation and the catalytic properties of the ATPase molecule.     

Reversible binding of Pi by beef heart mitochondrial adenosine triphosphatase.

Beef heart mitochondrial ATPase (F1) exhibited a single binding site for Pi. The interaction with Pi was reversible, partially dependent on the presence of divalent metal ions, and characterized by a dissociation constant at pH 7.5 of 80 micronM. A variety of substances known to influence oxidative phosphorylation or the activity of the soluble ATPase (F1) also influenced Pi binding by the enzyme. Thus aurovertin, an inhibitor of oxidative phosphorylation, which was bound tightly by F1 and inhibited ATPase activity, enhanced Pi binding via a 4-fold increase in the affinity of the enzyme for Pi (KD = 20 micronM) but did not alter binding stoichiometry. Anions such as SO4(2-), SO3(2-), chromate, and 2,4-dinitrophenolate, which stimulated ATPase activity of F1, also enhanced Pi binding. Inhibitors of ATPase activity such as nickel/bathophenanthroline and the protein ATPase inhibitor of Pullman and Monroy (Pullman, M. E., and Monroy, G. C. (1963) J. Biol. Chem. 238, 3762-3769) inhibited Pi binding. The adenine nucleotides ADP, ATP, and the ATP analog adenylyl imidodiphosphate as well as the Pi analog arsenate, also inhibited Pi binding. The observations suggest that the Pi binding site was located in or near an adenine nucleotide binding site on the molecule.     

Tightly bound magnesium in mitochondrial adenosine triphosphatase from beef heart.

Tightly bound magnesium was found in soluble, purified ATPase (F1) from beef heart mitochondria in the amount of 1 mol/mol of F1. Iron, zinc, cobalt, manganese, calcium, sodium, copper, and potassium were not tightly bound at stoichiometric levels. Removal of magnesium by chelating agents caused loss of ATPase activity. Removal of tightly bound nucleotide by gel filtration in 50% glycerol- or 60 mM K2SO4-containing buffers did not remove magnesium. Cold dissociation did release magnesium when complete denaturation was accomplished. The results suggest that magnesium is an integral part of F1, that it is required for activity, and that magnesium and nucleotides are tightly bound at separate sites. The idea that the tightly bound nucleotides are not complexed with cations suggests certain structural requirements at their binding sites which might account for the unusual properties of the sites.     

Effect of organic solvents on the beef heart mitochondrial adenosine triphosphatase.

The effect of organic solvents on the beef heart mitochondrial ATP-base-catalyzed ATP and ITP hydrolysis was examined. It was observed that numerous organic solvents stimulated ATP hydrolysis while ITP hydrolysis was inhibited. Methanol at 20% (v/v) was found to stimulate ATP hydrolysis by over 300%, while at the same methanol concentration ITP hydrolysis was inhibited approximately 50%. In the presence of 20% methanol, ATP hydrolysis exhibited linear plots of 1/[ATP] vs. 1/v, while in the absence of methanol negative cooperativity was observed. These data can be interpreted to imply that the catalytic and regulatory sites of the mitochondrial ATPase are being dissociated 20% methanol. The effect of methanol on the hydrolysis of ATP and ITP was examined as a function of pH. It was found that, at high pH in totally aqueous solutions, the hydrolysis of ATP and ITP was inhibited, while the presence of 20% methanol either caused the hydrolytic rate to peak and remain constant above pH 8 (with ATP as substrate) or caused the rate of hydrolysis to continue to increase above pH 8 (when ITP was the substrate). These data are interpreted to indicate that an acidic group in the active site may be ionizing, limiting the ATPase-catalyzed hydrolytic rate, and, with 20% methanol, this ionization was inhibited.     

Inhibition of chloroplast adenosine triphosphatase activity by adenosine triphosphatase inhibitor from beef heart mitochondria.

A new amino-acid sequence is proposed for silk fibroin peptide Cp, after automatic Edman degradation studies. The proposed sequence is: Gly-Ala-Gly-Ala-Gly-Ser-Gly-Ala-Ala-Gly-(Ser-Gly-(Ala-Gly)_n)₈ Tyr, where n is usually 2.     

Catalysis of partial reactions of ATP synthesis by beef heart mitochondrial adenosine triphosphatase

We have found that when the ATP hydrolysis activity of beef heart mitochondrial adenosine triphosphatase (F1) is eliminated by either cold treatment or chemical modification, the enzyme attains the ability to catalyze the Pi in equilibrium ATP exchange reaction. The ATP hydrolysis activity of isolated F1 was lost upon chemical modification by phenyglyoxal, butanedione, or 7-chloro-4-nitrobenzene-2-oxa-1,3-diazole. The F1 thus chemically modified was able to catalyze an ADP-dependent Pi in equilibrium ATP exchange reaction. In addition F1 that had been cold-treated to eliminate ATP hydrolysis activity, also catalyzed the Pi in equilibrium ATP exchange reaction. The Pi in equilibrium ATP exchange catalyzed by modified F1 was shown to be totally inhibited by the F1-specific antibiotic efrapeptin. We have previously shown that isolated beef heart mitochondrial ATPase will catalyze the formation of a transition state analog of the ATP synthesis reaction (Bossard, M. J., Vik, T. A., and Schuster, S. M. (1980) J. Biol. Chem. 255, 5342-5346). While the F1-catalyzed ATP hydrolysis activity was lost rapidly upon chemical modification or cold treatment, the ability of the enzyme to produce Pi . adenosine 5'-diphosphate (chromium(III) salt) from phosphate and monodentate adenosine 5'-diphosphate (chromium(III) salt) was unimpaired. The implications of these data with regard to the mechanism of ATP synthesis are discussed.     

Energy-dependent dissociation of ATP from high affinity catalytic sites of beef heart mitochondrial adenosine triphosphatase

Incubation of [gamma-32P]ATP with a molar excess of the membrane-bound form of mitochondrial ATPase (F1) results in binding of the bulk of the radioactive nucleotide in high affinity catalytic sites (Ka = 10(12) M-1). Subsequent initiation of respiration by addition of succinate or NADH is accompanied by a profound decrease in the affinity for ATP. About one-third of the bound radioactive ATP appears to dissociate, that is, the [gamma-32P]ATP becomes accessible to hexokinase. The NADH-stimulated dissociation of [gamma-32P]ATP is energy-dependent since the stimulation is inhibited by uncouplers of oxidative phosphorylation and is prevented by respiratory chain inhibitors. The rate of the energy-dependent dissociation of ATP that occurs in the presence of NADH, ADP, and Pi is commensurate with the measured initial rate of ATP synthesis in NADH-supported oxidative phosphorylation catalyzed by the same submitochondrial particles. Thus, the rate of dissociation of ATP from the high affinity catalytic site of submitochondrial particles meets the criterion of kinetic competency under the conditions of oxidative phosphorylation. These experiments provide evidence in support of the argument that energy conserved during the oxidation of substrates by the respiratory chain can be utilized to reduce the very tight binding of product ATP in high affinity catalytic sites and to promote dissociation of the nucleotide.     

Evidence supporting the identity of beef heart mitochondrial chloroform-released adenosine triphosphatase (ATPase) with coupling factor I.

Highly purified mitochondrial chloroform-released beef heart ATPase had molecular weight 330 000, five bands (alpha, beta, gamma, delta, epsilon) in sodium dodecyl sulfate gel electrophoresis and could restore the oxidative-phosphorylation function of A particles. Maximal inhibition (90%) of the enzyme by N,N'-dicyclohexylcarbodiimide was achieved at a molar ratio of inhibitor to protein of 30 : 1. Chloroform introduced into an aqueous solution of beef heart coupling factor I protected it from cold inactivation.     

Evidence supporting the identity of beef heart mitochondrial chloroform-released adenosine triphosphatase (ATPase) with coupling factor I

Highly purified mitochondrial chloroform-released beef heart ATPase had molecular weight 330 000, five bands (α, β, γ, δ, ε) in sodium dodecyl sulfate gel electrophoresis and could restore the oxidative-phosphorylation function of A particles. Maximal inhibition (90%) of the enzyme by N,N′-dicyclohexylcarbodiimide was achieved at a molar ratio of inhibitor to protein of 30 : 1. Chloroform introduced into an aqueous solution of beef heart coupling factor I protected it from cold inactivation.     

Purification and properties of adenosine triphosphatase solubilized from beef heart mitochondria by chloroform

Summary Soluble, oligomycin-insensitive ATPase released from beef heart mitochondria by chloroform extraction can be further purified by Sepharose 6B gel filtration. This purification increases enzyme activity 4–5 times (100–130 U/mg). According to specific activity, high purity and ability to reconstitute oligomycin-sensitive complex, isolated ATPase is quite comparable with enzyme preparations isolated by other methods.     

Kinetic studies on rat liver and beef heart mitochondrial adenosine triphosphatase: the effects of the chromium complexes of adenosine triposphate and adenosine diphosphate on the kinetic properties.

The kinetics of isolated rat liver and beef heart mitochondrial adenosine triphosphatase (ATPase) were studied by using the chromium ATP and ADP complexes as substrate analogs. It was found that both chromium ATP (CrATP) and chromium ADP (CrADP) are competitive inhibitors of ATP hydrolysis. The presence or absence of ATPase-activating anions, e.g., bisulfite, had little effect on the type or potency of the inhibition by these chromium complexes. Both CrADP and CrATP were noncompetitive inhibitors of the hydrolysis of ITP with both the heart and liver-derived enzymes. It was also found that CrADP was a consistently more effective inhibitor than the ATP complex with the beef heart enzyme. These results are consistent with the existence of two types of nucleotide binding sites on mitochondrial ATPases: One site is regulatory and is rather specific for adenosine polyphosphates, while the other site is relatively nonspecific and serves as the hydrolytic site.