Studies on oxidative phosphorylation. XV. Latent adenosine 5'-triphosphatase activity of factor A

Mitochondrial ATPase

Considerable progress has been made in recent years in our understanding of the phosphorylating apparatus in mitochondria, chloroplasts, and bacteria. It has become clear that the structure and the function of the ATP synthesizing apparatus in these widely divergent organisms is similar if not virtually identical. The subunit composition of F1, its molecular architecture, the location and function of substrate binding sites, as well as putative control sites, understanding of the component parts of the oligomycin-sensitive ATPase complex, and the role of these components in the function of the complex all are under active investigation in many laboratories. The developing information and the new insights provided have begun to permit experimental approaches, at the molecular level, to the mode of action of the ATPase in electron-transport-coupled ATP synthesis.

Distribution of the ATPase inhibitor proteins of mitochondria in mammalian tissues including fibroblasts from a patient with Luft's disease

The mitochondrial ATPase inhibitor proteins--the Pullman-Monroy inhibitor (PMI) and the Ca(2+)-binding protein (CaBI)--have a wide distribution, both being present in mitochondria of bovine heart and kidney, rat liver and brain, two mitochondrial populations of rabbit skeletal muscle, and mitochondria from human fibroblasts and the human breast cancer cell line T-47-D. The ratio of CaBI to PMI was highest in heart and skeletal muscle mitochondria. The subsarcolemmal fraction of skeletal muscle had 2.6-times as much CaBI as did the intermyofibrillar. The ratio of CaBI to PMI in the mitochondria of the other normal tissues and fibroblasts was close to 1. In contrast, mitochondria from T-47D cells had 1.5-times as much PMI as CaBI whilst mitochondria from fibroblasts from a patient with Luft's disease showed a virtual lack of PMI. The specific ATPase, ATP-synthetase and succinate dehydrogenase activities of the Luft's mitochondria were, however, in the normal range. The specific ATP synthetase activity of the T-47D cells was significantly higher than normal. We conclude that tissues like heart and skeletal muscle which experience wide fluctuations in intracellular Ca2+ have a greater need for CaBI. Why lack of PMI could lead to 'loose' coupling of oxidative phosphorylation in skeletal muscle of Luft's patients, but not in fibroblasts is discussed.

Isolation of two ATPase inhibitor proteins from mitochondria of rat skeletal muscle

An ATPase inhibitor protein was isolated from mitochondria of rat skeletal muscle by alkaline extraction and then was purified. It differed in definitive ways from the ATPase inhibitor protein isolated previously by Ca2+-stripping of submitochondrial particles of rat skeletal muscle. The two ATPase inhibitor proteins were shown to be present together in intact mitochondria.

Use of trypsin to monitor conformational changes of mitochondrial adenosinetriphosphatase induced by nucleotides and phosphate

Upon incubation with trypsin, the adenosine-5'-triphosphatase (ATPase) activity of the nucleotide-depleted F1 is first rapidly and slightly activated and then slowly inactivated. The first phase is simultaneous with the conversion of the alpha subunit into an alpha' fragment which migrates between alpha and beta on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The second phase is related to the proteolysis of the three main subunits, alpha', beta, and gamma. Preincubation of the enzyme with low concentrations of adenosine 5'-diphosphate (ADP) or adenosine 5'-triphosphate (ATP) does not modify the slight increase of activity but efficiently prevents the inactivation induced by trypsin. The alpha leads to alpha' conversion is not affected whereas the further proteolysis of alpha', beta, and gamma does not occur. On the contrary, even high concentrations of GDP only slightly lower the trypsin-induced inactivation. The presence of endogenous tightly bound nucleotides also partially lowers the sensitivity to trypsin since F1 is less rapidly inactivated and proteolyzed than the nucleotide-depleted F1. Phosphate, at high concentrations, both slows down the first phase of activation and simultaneous alpha leads to alpha' conversion and prevents the second phase of inactivation and proteolysis of the main subunits. Pretreatment of the nucleotide-depleted F1 with trypsin under conditions where the ATPase activity is largely inhibited only slightly modifies, however, the hysteretic behavior of the enzyme: the ADP binding and the concomitant hysteretic inhibition of the residual activity are not markedly diminished. The purified ATPase-ATP synthase complex binds very few ADP's and is not hysteretically inhibited. Its ATPase activity is rapidly activated but not further inhibited by trypsin. Preincubation of the complex with ADP does not modify the effects of trypsin.

Further studies on F1-ATPase inhibition by local anesthetics

We have measured the inhibitory potencies of several local anesthetics (procaine, lidocaine, tetracaine and dibucaine) and related compounds (chlorpromazine, procainamide and propranolol) on the ATPase activities of bovine heart submitochondrial particles and purified F1 extracted from these particles. All of these agents cause inhibition of ATPase in F1 as well as in submitochondrial particles. A linear relationship is found between the log of the octanol/water partition coefficients and the log of the concentrations required for 50% inhibition of F1. Sedimentation velocity ultracentrifugation and polyacrylamide gel electrophoresis showed that 1.0 mM tetracaine caused partial dissociation of the F1 complex. Complete reversibility of the enzyme inhibitory effects was demonstrated, however. This work shows that local anesthetics can affect protein structure and enzyme activity without the mediation of lipid.

Involvement of the endogenous inhibitor protein in the MgATP-induced inhibition of soluble mitochondrial adenosine triphosphatase activity

Chloroform-released ATPase from ox heart mitochondria contains significant amounts of inhibitor protein. There is a correlation between processes that affect the interactions between the inhibitor protein and the ATPase molecule and the ability of MgATP to induce an inhibition of ATPase activity. Evidence is presented suggesting that the endogenous inhibitor protein is involved in the process of MgATP-induced inhibition of soluble ATPase activity.

MgATP-induced inhibition of the adenosine triphosphatase activity of submitochondrial particles

1. The ATP-hydrolytic activity of ox heart submitochondrial particles can be increased from 2-3 mumol/min per mg of protein to 10-12 mumol/min per mg of protein by incubation in media containing 50 mM-Na2B4O7. This process appears to be due to the partial release of inhibitor protein from the particles. 2. The ATPase activity of submitochondrial particles can be inhibited by incubation with the substrate, MgATP. This inhibition is not due to the accumulation of the hydrolysis products, MgADP and Pi, but could involve the process of ATP hydrolysis. 3. The mechanism of MgATP-induced inhibition of ATPase activity is proposed to involve a conformational change in one of the intermediate enzyme species of the ATP-hydrolytic sequence. 4. MgATP inhibits the ATPase activity of control submitochondrial particles at a higher rate and to a greater extent than it does that of inhibitor-protein-depleted submitochondrial particles, suggesting that the conformational change involves the endogenous inhibitor protein.

F1-ATPase from different submitochondrial particles

1. F1-ATPase has been extracted by the diphosphatidylglycerol procedure from mitochondrial ATPase complexes that differ in ATPase activity, cold stability, ATPase inhibitor and magnesium content. 2. The ATPase activity of the isolated enzymes was dependent upon the activity of the original particles. In this respect, F1-ATPase extracted from submitochondrial particles prepared in ammonia (pH 9.2) and filtered through Sephadex G-50 was comparable to the enzyme purified by conventional procedures (Horstman, L.L. and Racker, E. (1970) J. Biol. Chem. 245, 1336--1344), whereas F1-ATPase extracted from submitochondrial particles prepared in the presence of magnesium and ATP at neutral pH was similar to factor A (Andreoli, T.E., Lam, K.W. and Sanadi, D.R. (1965) J. Biol. Chem. 240, 2644--2653). 3. No systematic relationship has been found in these F1-ATPase preparations between their ATPase inhibitor content and ATPase activity. Rather, a relationship has been observed between this activity and the efficiency of the ATPase inhibitor-F1-ATPase association within the membrane. 4. It is concluded that the ATPase activity of isolated F1-ATPase reflects the properties of original ATPase complex provided a rapid and not denaturing procedure of isolation is employed.

Optical properties and denaturation by guanidinium chloride and urea of the adenosine triphosphatase of Micrococcus lysodeikticus. A comparison of four molecular forms of the enzyme

1. The fluorescence and circular dichroism of four homogeneous preparations of ATPase (adenosine triphosphatase) from Micrococcus lysodeikticus differing in molecular structure and enzymic properties were examined at pH 7.5 and 25 degrees. Emission was maximum at 325 and 335 nm and the relative intensities at these wavelengths may be used to characterize the different ATPase preparations. The circular-dichroism spectra exhibited negative extrema at 208 and 220 nm, and the relative value of the molar ellipticity at these wavelengths was also different for each molecular form of the enzyme. 2. The four preparations undergo two consecutive major unfolding transitions in guanidinium chloride (midpoints at 0.94 and 1.5 M denaturant), with concomitant destruction of the quaternary structure of the protein. A comparatively minor alteration in the ATPase structure also occurred in 0.05-0.2M-guanidine and led to complete inactivation of the enzyme. The inactivation and the first unfolding transition were reversible by dilution of the denaturant; the transition with midpoint at 1.5M-guanidine was irreversible. 3. Similar results were obtained in urea, except that the successive transitions had midpoints at concentrations of denaturant of 0.4, 2.0 and 4.5M. Low concentrations of urea caused a noticeable activation of the enzyme activity and alterations of the electrophoretic mobility of the ATPase. 4. A model is proposed in which one of the major subunits, alpha, is first dissociated and unfolded reversibly by the denaturants, followed by the irreversible unfolding and dissociation of the other major subunit, beta, from subunit delta and/or the components of relative mobility 1.0 in dodecyl sulphate/polyacrylamide-gel electrophoresis (rho).

Molecular polymorphism and mechanisms of activation and deactivation of the hydrolytic function of the coupling factor of oxidative phosphorylation

The 13S coupling factor of oxidative phosphorylation from Alcaligenes faecalis has a latent adenosine triphosphatase (ATPase) function that can be activated by heating at 55 degrees C for 10 min at pH 8.5 in 50% glycerol. The specific activity increases from 0.1 to 20--30 mumol min-1 mg-1. Adenosine 5'-triphosphate (ATP) is not required for stabilization at 55 degreesC when glycerol is present. Activation involves displacement of the endogenous ATPase inhibitor subunit (epsilon subunit), and readdition of this subunit results in deactivation. In the deactivation process the ATPase inhibitor subunit can be replaced by other cationic proteins such as protamine, histones, or poly(lysine). Mg2+ and H+ also are effective deactivators. The fact that every positively charged substance tested deactivated the enzyme suggests that the inhibitor subunit is complexed with the enzyme at a site containing a surplus of negative charges. The activated enzyme is not labile, but it is salt labile, having a half-life of 2-3 min in 0.1 M KI at either 25 or 0 degrees C. The activated ATPase is also inhibited by aurovertin, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD), and by the cross-linking agent dimethyl suberimidate. Evidence for polymorphism comes from finding that the properties of the unactivated enzyme (intrinsic ATPase) are different in many ways from the properties of activated ATPase. With respect to the coupling factor's ability to hydrolyze ATP, the data in this study suggest that there are at least four distinct functional allomorphs of this enzyme: (1) the latent enzyme, which has no kinetically measurable ATPase activity, (2) intrinsic ATPase, which is catalyzed by a small percentage of the molecular population that has been activated by some natural mechanism, (3) activated ATPase, which has properties different from those of intrinsic ATPase, and (4) aged activated ATPase, in which some of the properties (Km for substrate, sensitivity to deactivation by Mg2+ and H+) spontaneously change within 30 min.

Pig heart mitochondrial ATPase : properties of purified and membrane-bound enzyme. Effects of flavonoids

Soluble ATPase (F1) has been purified from pig heart mitochondria. The purified enzyme had a high specific activity and was homogeneous as checked by ultracentrifugation and electrofocusing. It could be dissociated into subunits by cold-treatment or sodium dodecyl sulfate denaturation. The molecular weights of the two major and three minor subunits could be estimated by sodium dodecyl sulfate gel electrophoresis. The native enzyme had an isoelectric point of 5.2 while the cold-denatured enzyme showed three main bands focusing at pH 5.0, 5.2, and 5.4. Kinetic properties (Vm and Km (atp) have been compared for the soluble and membrane bound ATPase in presence of various anions. Inhibitory effects of Quercetin and other flavonoids have been tested in order to get an insight on the interaction between ATPase and its natural inhibitor.

Electrophoretic microheterogeneity and subunit composition of the 13S coupling factors of oxidative and photosynthetic phosphorylation

Two electrophoretically distinguishable species of the 13S coupling factor of oxidative phosphorylation from Alcaligenes faecalis are detectable by standard polyacrylamide gel electrophoresis in the absence of urea, detergents, or any other protein-denaturing reagents. The slower species (type IA) can be converted into the faster species (type IB) by treatment with ATP, and the fast form converts into the slow form when aged at 4 degrees. The enzyme undergoes these conversions both when it is free in solution and when it is membrane bound. The ATP analog adenylyl imidodiphosphate (AMP-PNP) gives the conversion without being hydrolyzed and without causing any apparent change in the mass of the protein, which suggests that the conversion may be a ligand-induced conformational change. Types IA and IB can convert into three other electrophoretically distinguishable species (types IIA, IIB, and III) if the purification procedure involves chromatography on a DEAE-Sephadex column equilibrated in phosphate buffer. These conversions can be prevented if the column is eluted in morpholinoethanesulfonic acid (Mes) buffer and KCl. Type IIA is convertible into type IIB by ATP treatment. Types IA and IB will also convert into types IIA and IIB and finally into type III when aged for extended periods of time at 4 degrees, without a detectable change in mass. Coupling factor activity is lost when type I enzyme converts into type II enzyme, as is the ability of the enzyme to bind to the membrane. However, ATPase activity does not change significantly. The mitochondrial 13S coupling factor shows up to three electrophoretically distinguishable species. The use of phosphate buffer during DEAE-Sephadex chromatography gives conversion of slower species into faster species. ATP treatment does not give interconversions, and aging at 4 degrees gives only a slow dissociation of the enzyme into subunits. The chloroplast 13S coupling factor also shows up to three electrophoretic species. Incubation with ATP does not give interconversions, but a temperature-dependent conversion of the major species into a faster species occurs upon aging. The subunit composition of the three 13S enzymes is very similar by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, the major difference being in the number of classes of small polypeptides.

The role of Factor B in the energy transfer reactions of oxidative phosphorylation

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