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

Kinetic and hysteretic behavior of ATP hydrolysis of the highly stable dimeric ATP synthase of Polytomella sp

The F1FO-ATP synthase of the colorless alga Polytomella sp. exhibits a robust peripheral arm constituted by nine atypical subunits only present in chlorophycean algae. The isolated dimeric enzyme exhibits a latent ATP hydrolytic activity which can be activated by some detergents. To date, the kinetic behavior of the algal ATPase has not been studied. Here we show that while the soluble F1 sector exhibits Michaelis-Menten kinetics, the dimer exhibits a more complex behavior. The kinetic parameters (Vmax and Km) were obtained for both the F1 sector and the dimeric enzyme as isolated or activated by detergent, and this activation was also seen on the enzyme reconstituted in liposomes. Unlike other ATP synthases, the algal dimer hydrolyzes ATP on a wide range of pH and temperature. The enzyme was inhibited by oligomycin, DCCD and Mg-ADP, although oligomycin induced a peculiar inhibition pattern that can be attributed to structural differences in the algal subunit-c. The hydrolytic activity was temperature-dependent and exhibited activation energy of 4 kcal/mol. The enzyme also exhibited a hysteretic behavior with a lag phase strongly dependent on temperature but not on pH, that may be related to a possible regulatory role in vivo.

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.

The native F0F1-inhibitor protein complex from beef heart mitochondria and its reconstitution in liposomes

A functional F0F1 ATP synthase that contains the endogenous inhibitor protein (F0F1I) was isolated by the use of two combined techniques [Adolfsen, R., McClung, J.A., and Moudrianakis, E. N. (1975). Biochemistry 14, 1727-1735; Dreyfus, G., Celis, H., and Ramirez, J. (1984). Anal. Biochem. 142, 215-220]. The preparation is composed of 18 subunits as judged by SDS-PAGE. A steady-state kinetic analysis of the latent ATP synthase complex at various concentrations of ATP showed a Vmax of 1.28 mumol min-1 mg-1, whereas the Vmax of the complex without the inhibitor was 8.3 mumol min-1 mg-1. In contrast, the Km for Mg-ATP of F0F1I was 148 microM, comparable to the Km value of 142 microM of the F0F1 complex devoid of IF1. The hydrolytic activity of the F0F1I increased severalfold by incubation at 60 degrees C at pH 6.8, reaching a maximal ATPase activity of 9.5 mumol min-1 mg-1; at pH 9.0 a rapid increase in the specific activity of hydrolysis was followed by a sharp drop in activity. The latent ATP synthase was reconstituted into liposomes by means of a column filtration method. The proteoliposomes showed ATP-Pi exchange activity which responded to phosphate concentration and was sensitive to energy transfer inhibitors like oligomycin and the uncoupler p-trifluoromethoxyphenylhydrazone.

Control of mitochondrial ATP synthesis in the heart

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Proton ATPase of rat liver mitochondria: a rapid procedure for purification of a stable, reconstitutively active F1 preparation using a modified chloroform method

A method is described for the purification of rat liver F1-ATPase by a modification of the chloroform extraction procedure originally described by Beechey et al. (Biochem. J. (1975) 148, 533). Purified liver membrane vesicles are extracted with chloroform in the presence of ATP and EDTA. The procedure yields pure F1 in only 2-3 h without the necessity of ion-exchange chromatography. The enzyme exhibits the alpha, beta, gamma, delta, and epsilon bands characteristic of F1-ATPase. It has a high ATPase specific activity, and is reconstitutively active, catalyzing high rates of ATP synthesis. Significantly, it can be readily crystallized. If desired, the enzyme can be passed over a gel filtration column to place it in a stabilizing phosphate-EDTA buffer, lyophilized and stored indefinitely at -20 degrees C.

Hydrophobic and ionic effects upon the electrophoretic mobilities of the subunits of coupling factor 1 from mitochondria

A sodium dodecyl sulfate (SDS)-urea polyacrylamide gel system was used to investigate certain properties of the subunits of the beef heart mitochondrial ATPase, (native F1, nF1). By examining the affects of urea concentration and acrylamide concentration upon the electrophoretic mobilities of the polypeptides comprising the nF1 enzyme, we have obtained conditions under which all five subunits are simultaneously resolved when the discontinuous buffer system of Laemmli is used (U. K. Laemmli (1970) Nature (London) 277, 680-685). The determination of the apparent molecular weights by analysis of Ferguson plots (K. A. Ferguson (1964) Metabolism 13, 985-1002) revealed that the addition of urea to the SDS gels resulted in a decrease in the apparent molecular weight of the beta subunit. A dramatic increase in the apparent molecular weight of the delta subunit was also brought about by the presence of urea in the SDS gels. In addition, the apparent molecular weight of both the alpha and the beta subunits was dependent upon the acrylamide concentration used, indicating that these subunits contain either areas highly resistant to denaturation by the combined action of urea and SDS, or covalent modifications leading to anomalous electrophoretic mobility. The results of experiments in which urea analogs were used indicate that the interactions of urea with the beta subunit involve the formation of hydrogen bonds between urea and regions of this subunit. On the other hand, the interactions of urea with the delta subunit are primarily of a hydrophobic nature, suggesting that these interactions could involve domains of the delta subunit required for binding of the coupling factor to the mitochondrial membrane.

Classification of nucleotide binding sites on mitochondrial F1-ATPase from yeast

Methods are described to classify nucleotide binding sites of the mitochondrial coupling factor F1 from yeast on the basis of their affinities and stability properties. High affinity sites or states for ATP and related adenine analogs and low affinity sites or states which bind a broad range of different nucleotide triphosphates are found. The results are discussed in terms of a two site, two cycle scheme, where binding of nucleotide at one site facilitates the release of nucleotide at a second site.

Activation parameters and molecular changes induced by substrate hydrolysis of the adenosine triphosphatase of Micrococcus lysodeikticus. A comparison of three different soluble forms of the enzyme

The Arrhenius plots for the active and low activity soluble forms of the ATPase purified from the membranes of Micrococcus lysodeikticus grown at 30 degrees C presented discontinuities at 30 and 33 degrees C, respectively. Their activation parameters differed, being highest for the low activity form of the enzyme. Both forms underwent changes in their molecular properties as a consequence of being enzymically active, i.e., upon incubation with substrates at an adequate temperature. These changes consisted of a decrease in the relative mobilities of some of their subunits in dodecyl sulphate polyacrylamide gel electrophoresis, and the temperature at which they occurred depended on the energy of activation of the particular form of the ATPase used. The low activity form required an incubation temperature of 50 degrees C, whereas for an active form 37 degrees C was sufficient.

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.

Membrane adenosine triphosphatase of Micrococcus lysodeikticus. ISolation of two forms of the enzyme complex and correlation between ezymatic stability, latency and activity

Two new forms of the plasma membrane ATP-ase of Micrococcus lysodeikticus NCTC 2665 were isolated from a sub-strain of the microorganism by polyacrylamide gel electrophoresis. One of them had a mol.wt of 368,000 and a very low specific activity (0.80 mumol.min-1.mg protein-1) that could not be stimulated by trypsin. This form has been called B1 (strain B, inactive). If the elctrophoresis was carried out in the presence of reducing agents (i.e., dithiothreitol) and the pH of the effluent maintained at a value of 8.5 another form of the enzyme was obtained. This had a mol.wt of 385,000 and a specific activity of 2.5-5.0 mumol.min-1.mg protein-1 that could be stimulated by trypsin to 5-10 mumol.min-1.mg protein-1. This preparation of the ATPase has been called from BA (strain B, enzyme active). The subunit composition of both forms has been studied by sodium dodecyl sulphate and urea gel electrophoresis and compared to that of the enzyme previously purified from the original strain (form A). The three forms of the enzyme had similar beta and delta subunits, with mol.wt of about 50,000 and 30,000 dalton, respectively. They also had in common the component(s) of relative mobility 1.0, whose status as true subunit(s) of the enzyme remains yet to be established. However, subunit alpha, that had a mol.wt of about a 52,500 in form A (ANDREU et al. Eur. J. Biochem. (1973) 37, 505-515), had a mol.wt similar to beta in form B1 and about 60,000 in form BA. Furthermore BA usually showed two types of this subunit (alpha' and alpha") and an additional peptide chain E) with a mol.wt of about 25,000 dalton. This latter subunit seemed to account for the stimulation by trypsin of form BA. Forms BA could be converted to B1 by storage and freezing and thawing. Conventional protease activity could not be detected in any of the purified ATPase forms and addition of protease inhibitors to form BA failed to prevent its conversion to form B1. The low activity form (B1) was more stable than the active forms of the enzyme and also differeed in its circular dichroism. These results show that M. lysodeikticus ATPase can be isolated in several forms. Although these variations may be artifacts caused by the purification procedures, they provide model systems for understanding the structural and functional relationships of the enzyme and for drawing some speculations about its function in vivo.