Fluorescence change of auramine O bound to chromatophores of Rhodospirillum rubrum--analysis in connection to ionic environment and ion transport

Catalytic mechanism of F1-ATPase

The structure of the core catalytic unit of ATP synthase, alpha 3 beta 3 gamma, has been determined by X-ray crystallography, revealing a roughly symmetrical arrangement of alternating alpha and beta subunits around a central cavity in which helical portions of gamma are found. A low-resolution structural model of F0, based on electron spectroscopic imaging, locates subunit a and the two copies of subunit b outside of a subunit c oligomer. The structures of individual subunits epsilon and c (largely) have been solved by NMR spectroscopy, but the oligomeric structure of c is still unknown. The structures of subunits a and delta remain undefined, that of b has not yet been defined but biochemical evidence indicates a credible model. Subunits gamma, epsilon, b, and delta are at the interface between F1 and F0; gamma epsilon complex forms one element of the stalk, interacting with c at the base and alpha and beta at the top. The locations of b and delta are less clear. Elucidation of the structure F0, of the stalk, and of the entire F1F0 remains a challenging goal.

Rapid purification and characterization of F1-ATPase of Vibrio parahaemolyticus

The F1 portion of H(+)-translocating ATPase as purified from membrane vesicles of Vibrio parahaemolyticus by a rapid procedure. The whole purification process (from culture of cells to purification of the enzyme) could be completed in 1 day. The F1-ATPase consists of five subunits (alpha, beta, gamma, delta and epsilon) like F1 of Escherichia coli and other microorganisms. The F1-ATPase of V. parahaemolyticus showed some interesting properties. Its activity was greatly stimulated by high concentrations (about 0.5 M) of SO4(2-), SO3(2-) and CH3COO-, their effects decreasing in this order. Among the anions tested, Cl- and NO3- were ineffective, or rather inhibitory, and cations had no significant effects. Ethanol (or methanol) stimulated the activity 2- to 3-fold. The activity was inhibited by 4-acetamido-4'-isothiocyanostilbene 2,2'-disulfonate (SITS) (an anion exchanger inhibitor), tetrachlorosalicylanilide (TCS) (an H+ conductor), azide and N-ethylmaleimide. Zinc inhibited the activity only slightly, although it strongly inhibited the ATPase activity in membrane vesicles.

SecA protein: autoregulated initiator of secretory precursor protein translocation across the E. coli plasma membrane

Several classes of secA mutants have been isolated which reveal the essential role of this gene product for E. coli cell envelope protein secretion. SecA-dependent, in vitro protein translocation systems have been utilized to show that SecA is an essential, plasma membrane-associated, protein translocation factor, and that SecA's ATPase activity appears to play an essential but as yet undefined role in this process. Cell fractionation studies suggested that SecA protein is in a dynamic state within the cell, occurring in soluble, peripheral, and integral membraneous states. These data have been used to argue that SecA is likely to promote the initial insertion of secretory precursor proteins into the plasma membrane in a manner dependent on ATP hydrolysis. The protein secretion capability of the cell has been shown to translationally regulate secA expression with SecA protein serving as an autogenous repressor, although the exact mechanism and purpose of this regulation need to be defined further.

Promotion and inhibition of catalytic cooperativity of the Ca2+-dependent ATPase activity of spinach chloroplast coupling factor 1 (CF1)

ATP- and ITP-stimulation of the Ca2+-dependent hydrolysis of low concentrations of [gamma-32P]ATP was used as a direct demonstration of catalytic cooperativity in CF1. CF1 activated by epsilon-subunit removal or dithiothreitol, or by the presence of ethanol in the ATPase assay medium, shows pronounced catalytic cooperativity, with maximal stimulation of [gamma-32P]ATP hydrolysis at about 20 microM CaATP. Catalytic cooperativity is diminished by the presence of the epsilon-subunit or by pretreatment of either untreated or epsilon-depleted CF1 with azide (C1/2=30 microM). Both activated and untreated forms of CF1 also exhibit hydrolysis of CaATP by a high-affinity, low-capacity mode of turnover, which is unaffected by any of the preceding treatments and shows normal Michaelis-Menten behaviour. We propose that this high-affinity mode represents unisite catalysis, and that the endogenous inhibitor, epsilon, and the exogenous inhibitor, azide, both act exclusively on cooperative interactions between the catalytic sites.

Characterization of the membrane-bound ATPase from a facultatively anaerobic alkalophile

We have studied the properties of membrane-bound ATPase of a facultatively anaerobic alkalophile. The enzyme could not be solubilized without detergent, suggesting an integral membrane protein. The activity was accelerated by NH4+ and acetate anion, and inhibited by NH3-. The enzyme required Mg2+ or Mn2+ as a divalent cation for the maximal activity. In addition to ATP, the enzyme utilized other triphosphates of nucleosides as a substrate, but not di- nor monophosphates. The enzyme was suggested to crossreact with an antibody against the alpha-subunit of Na+/K+-ATPase from dog kidney.

Distinct phases of the fluorescence response of the lipophilic probe N-phenyl-1-naphthylamine in intact cells and membrane vesicles of Escherichia coli

The fluorescence of the lipophilic probe N-phenyl-1-naphthylamine (NPN) bound to intact cells of Escherichia coli is quenched by the addition of glucose, succinate, D-lactate, pyruvate, formate and glycerol. Partial recovery of fluorescence occurs on anaerobiosis. Use of mutants with defects in the ATP synthase or the respiratory chain show that quenching of fluorescence may be energized either by ATP hydrolysis or by substrate oxidation through the respiratory chain. Permeabilization of the outer membrane by treatment of intact cells with EDTA, or use of a mutant with an outer membrane permeable to lipophilic substances, results in a more rapid binding of NPN and in a decrease in quenching observed on substrate addition. NPN binds rapidly to everted membrane vesicles, but does not respond to membrane energization. It is proposed that inner membrane energization in intact cells alters the binding or environment of NPN in the outer membrane. The fluorescence recovery which occurs on anaerobiosis has two components. One component represents a reversal of the changes which occur on membrane energization. The other component of the fluorescence change is insensitive to the uncoupler CCCP and resembles the behaviour of NPN with everted membrane vesicles. It is suggested that a portion of the fluorescence events seen with NPN involves a response of the probe to changes in the inner membrane.

Mode of inhibition of sodium azide on H+-ATPase of Escherichia coli

Sodium azide inhibited multi-site (steady-state) ATPase activity of E. coli F1 more than 90%, but did not affect uni-site (single-site) ATPase activity. Thus azide inhibited multi-site ATPase activity by lowering catalytic cooperativity. Consistent with this observation, azide changed the ligand-induced fluorescence response of aurovertin bound to F1.

Purification and characterization of the soluble form of mitochondrial adenosine triphosphatase from sweet potato

The soluble form of mitochondrial adenosine triphosphatase was purified in an electrophoretically and immunologically pure form from sweet potato root tissue. The enzyme consisted of six kinds of subunits with different molecular weights (52,500, 51,500, 35,500, 26,000, 23,000, and 12,000), and its molecular weight was about 370,000. Adenosine triphosphatase associated with the submitochondrial particles was oligomycin-sensitive and heat-labile, whereas the soluble form of the enzyme was oligomycin-insensitive and cold-labile. The enzyme in either the membrane-bound or the soluble form showed negative cooperativity. Both experiments with polyacrylamide gel electrophoresis and immunological methods suggest that some of the subunits, probably those with molecular weights of 52,500 and 51,500, are dissociated from the enzyme protein during storage of the enzyme preparations.

Properties of apyrase and inorganic pyrophosphatase in Streptomyces aureofaciens

Apyrase (ATP-diphosphohydrolase, EC 3.6.1.5) and inorganic pyrophosphatase (EC 3.6.1.1) were partially purified from S. aureofaciens RIA 57 and characterized. Apyrase degrades, in addition to ATP, other nucleoside triphosphates and nucleoside diphosphates, diphosphate, thiamine diphosphate, phosphoenolpyruvate and oligophosphates of chain length n less than 90. The apyrase activity was detected in the membrane and supernatant fractions. Its properties (substrate specificity. effect of inhibitors, pH optimum and effect of Mg2+ ions) were similar in both fractions except for the effect of oligomycin that inhibited only the membrane fraction. Pyrophosphatase exhibited a strict substrate specificity, substrates other than diphosphate being degraded relatively slowly. Of other enzymes exhibiting the phosphatase activity acid phosphatase (EC 3.1.3.2) and alkaline phosphatase (EC 3.1.3.1), trimetaphosphatase (EC 3.6.1.2) and exopolyphosphatase (EC 3.6.1.11) degrading oligophosphatase of chain length n = 15, 40 and 60, were detected.

Partial characterization and inactivation of membrane-bound phosphofructokinase from Tetrahymena pyriformis

In Tetrahymena pyriformis, 6-phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) is membrane-bound. Enzyme activity is solubilized by treatment of membranes with Triton X-100 or by high ionic strength in the presence of a chelator. The solubilized enzyme has an approximate molecular weight of 300 000. Both the membrane-bound enzyme and the solubilized enzyme exhibit maximum activity over a wide pH range. At low pH, the membrane-bound form of the enzyme is irreversibly inactivated, whereas the solubilized enzyme is not. The membrane-bound enzyme is inactivated by incubation with Mg2+, ATP, fluoride and a soluble factor that is heat labile, nondialysis, (NH4)2SO4 precipitable and sensitive to trypsin. The solubilized enzyme is not inactivated under similar conditions.

Membrane-bound cooperative enzymes. Stokes' radii, Hill plots and membrane fluidity in the regulation of adenosinetriphosphatase from Escherichia coli

The soluble Ca2+-ATPase from Escherichia coli had a distinctive behavior with respect to inhibition by Na+ measured at 36 degrees C and 19 degrees C. At the first temperature the Hill plots are linear and show a slope of 1.1 while at 19 degrees C the plots are biphasic, with slopes of 1.8 and 0.8 before and after the break, respectively. The break occurs at about 50 nM NaCl. Gel chromatography was performed in jacketed Sepharose 4B columns kept at 2 temperatures in the presence of different concentrations of NaCl. It was found that the Stokes' radius of the enzyme was dependent on the temperature and on the salt concentration. Equilibrium sucrose gradients run at 19 degrees C showed that the sedimentation constant of the enzyme remained constant irrespective of the NaCl concentration used. It is concluded that a "folding" of the enzyme takes place in the presence of NaCl, the process being complete at about 50 mM NaCl at 19 degrees C and at about 20 mM at 36 degrees C. The results are in excellent agreement with the kinetic data: the "folded" or "compact" configuration would show no cooperative response towards Na+ while the "expanded" conformer would present strong cooperativity. This is also in agreement with the results obtained with the enzyme embedded in the membrane: when the membrane is fluid a high n value (Hill coefficient) is found; when the membrane is more rigid the value of n falls. A model explaining all our results is proposed and discussed.

Membrane reconstitution in chl-r mutants of Escherichia coli K 12. VII. Purification of the soluble ATPase of supernatant extracts and kinetics of incorporation into reconstituted particles

Membrane-bound ATPase (EC 3.6.1.3) of Escherichia coli K 12 is released in a soluble form by the mechanical treatments applied to the cells in order to break them. The purification of the soluble enzyme is described. The purified protein gives a single band in 7.5% polyacrylamide gel electrophoresis. The molecular weight is estimated to be 350 000. The enzyme is cold-labile, Mg-2+ dependent, insensitive to inhibition by N, N'-dicyclohexylcarbodiimide and specific for ATP and ADP. Membranes depleted of their ATPase activity by dilution in a buffer of low ionic strength and without Mg-2+ are able to incorporate the purified ATPase only in the presence of 2-6 mM Mg-2+. ATPase binds to particles formed by complementation between supernatant extracts of chl A and chl B mutants. There are three kinds of particles of different buoyant densities (1.10, 1.18 and 1.23); ATPase binds only to the 1.10 and 1.18 particles. The kinetics of incorporation have been studied. ATPase begins to be incorporated into the 1.10 particles after 10 min of incubation up to a maximum at 20 min: from 30 min, ATPase is incorporated only into 1.18 particles and the amount of incorporated ATPase increased in proportion with the peak of 1.18 particles. These kinetics have a hyperbolic pattern. In order to explain the mechanism of assembly involved in complementation, two hypotheses are proposed.

Nucleotide-binding properties of native and cold-treated mitochondrial ATPase

1. The bound nucleotides of the beef-heart mitochondrial ATPase (F1) are lost during cold inactivation followed by (NH4)2SO4 precipitation. The release of tightly bound ATP parallels the loss of ATPase activity during this process. 2. During cold inactivation, the sedimentation coefficient (s20, w) of the ATPase first declines from 12.1 S to 9 S, then to 3.5 S. (NH4)2SO4 precipitation of the 9-S component also leads to dissociation into subunits with s20, w of 3.5 S. 3. The 9-S component still contains the bound nucleotides, which are removed when it dissociated into smaller subunits. 4. Reactivation of cold-inactivated ATPase by incubation at 30 degrees C is increased by the presence of 25% glycerol. ATP, however, does not have any clearcut effect on the degree of reactivation in the presence of glycerol. 5. ADP is an inhibitor of the reactivation, probably because it exchanges during reactivation for bound ATP giving rise to an inactive 12-S component. 6. The exchange of tightly bound nucleotides with added adenine nucleotides is more extensive and faster with cold-inactivated ATPase than with the native enzyme. During reactivation up to 1.6 moles of ATP and 1.0 mole ADP can exchange per mole enzyme. 7. Incubation with GTP, CTP or inorganic pyrophosphate induces an increased activity of the ATPase, which, however, soon declines in the presence of ATP. It also disappears on precipitation of GTP-treated enzyme with (NH4)2SO4.

Characterization of the mycoplasma membrane proteins. V. Release and localization of membrane-bound enzymes in Acholeplasma laidlawii

The peripheral membrane protein fraction released by washing Acholeplasma laidlawii membranes with low-ionic strength buffers contained about 50% of the total membrane-bound ribonuclease and deoxyribonuclease activities. The ATPase, NADH oxidase and p-nitrophenylphosphatase activities remained bound to the membrane even when EDTA was added to the wash fluids, and thus appear to belong to the integral membrane protein group. Serving as a marker for peripheral membrane proteins, the membrane-bound ribonuclease activity was solubilized by bile salts much more effectively than the integral membrane-bound enzymes. On the other hand, the solubilized ribonuclease showed a much lower capacity to reaggregate with other solubilized membrane components to membranous structures. Yet, most of the ribonuclease molecules which were bound to the reaggregated membranes could not be released by low-ionic strength buffer. The reaggregated membranes differed from the native membranes in the absence of particles on their fracture faces obtained by freeze cleaving, and by their much higher labeling by the [125-I]lactoperoxidase iodination system. These results suggest that most of the proteins are exposed on the reaggregated membrane surfaces, with very little, if any, protein embedded in its lipid bilayer core. Enzyme disposition in the A. laidlawii membrane was studied by comparing the activity of isolated membranes with that of membranes of intact cells after treatment with pronase or with an antiserum to membranes. The data indicate the asymmetrical disposition of these activities, the ATPase and NADH oxidase being localized on the inner membrane surface, while the nucleases are exposed on the external membrane surface.

The possible role of tightly bound adenine nucleotides in oxidative and photosynthetic phosphorylation

The tightly bound nucleotides of the beff-heart mitochondrial ATPase are released during cold inactivation followed by ammonium sulfate precipitation. During incubation at 0 degrees C the sedimentation coefficient (S20W) of the ATPase first declines from 12.1S to 9S. Prolonged incubation or precipitation with ammonium sulfate leads to dissociation of the 9S component into subunits with S20W of 3.5S. The 9S component still bears bound nucleotides which exchange more extensively and rapidly with added nucleotides than those bound to the active 12.1S component. The bound nucleotides are lost when the 9S form dissociates into the smaller subunits. Thus, firm binding of nucleotides is a property of the quarternary structure of the enzyme. The exchangeability of the nucleotides bound to the ATPase of chloroplast membranes is greatly increased in membranes illuminated in the presence of pyocyanine. Pi can exchange into both the beta and gamma positions of the bound nucleotides when the membranes are energized in the presence of Mg2+. The exchange of the nucleotides and the incorporation of Pi are insensitive to the inhibitor Dio-9 but are inhibited by the uncoupler S13. This inhibition by S13 parallels that of the inhibition of photosynthetic phosphorylation. These findings are discussed with regard to our hypothesis that electron transfer causes release of preformed tightly bound ATP from the ATPase by inducing a conformational change.