Reversible attachment of adenosine triphosphatase to streptococcal membranes and the effect of magnesium ions

Enzyme level of enterococcal F1Fo-ATPase is regulated by pH at the step of assembly

The amount of F1Fo-ATPase in Enterococcus hirae (formerly Streptococcus faecalis) increases when the cytoplasmic pH is lowered below 7.6, and protons are extruded to maintain the cytoplasmic pH at around 7.6. In the present study, we found that the transcriptional activity of the F1Fo-ATPase operon was not regulated by pH. The synthesis of F1 subunits was increased 1.65 +/- 0.12-fold by the acidification of medium from pH 8.0 to pH 5.3. Western-blot analysis showed that there were F1 subunits in the cytoplasm, and the number of alpha plus beta subunits in the cytoplasm was 50% of the total number of the subunits in cells growing at pH 8.0. This decreased to 22% after shifting the medium pH to 5.3, with a concomitant 5.1-fold increase in the level of membrane-bound F1Fo-ATPase. The cytoplasmic F1 subunits were shown to be degraded, and Fo subunits not assembled into the intact F1Fo complex were suggested to be digested. These data suggest that regulation of the enzyme level of F1Fo-ATPase by the intracellular pH takes place mainly at the step of enzyme assembly from its subunits.

Study of the lipid-protein interaction of F ATPases

Mg2+ may play a role in altering the lipid fluidity of the bilayers which would induce a change in conformation of the F0 portion of the H(+)-ATPase complex. This change could be transmitted to the soluble F1 portion, the conformation of which is in turn altered, resulting in higher enzymic activity. In addition to mitochondrial H(+)-ATPase, similar Mg2+ effects on the reconstitution of chloroplast H(+)-ATPase and other intrinsic membrane proteins have also been observed in our laboratory.

Further study on the role of Mg2+ in lipid-protein interaction in reconstituted porcine heart mitochondrial H+-ATPase

Porcine heart mitochondrial H+-ATPase was reconstituted by cholate dialysis method in liposomes containing neutral (PC, PE), acidic (PG, PI, PA, PS, DPG) or neutral and acidic phospholipids. The Mg2+ effect on the ATPase activity and its sensitivity to oligomycin, ATP-induced delta psi and delta pH formation was observed for the proteoliposomes containing acidic but not neutral phospholipids. Maleimide spin labels with varying arm lengths or bromoacetamide spin probe were used to monitor the conformational difference of H+-ATPase in the Mg2+-containing and Mg2+-'free' samples. A difference in W/S ratio (weakly immobilized/strongly immobilized component in the ESR spectra) could be detected for the F0.F1-containing and F1-depleted, (F0)-containing proteoliposomes, suggesting conformational difference in the F0-F1 complex and F0 portion induced by the Mg2+ effect. A conformational change of the beta-subunits in the F1 portion was also deduced from the ATP-induced fluorescence quenching of aurovertin-complex for Mg2+-containing samples. The results obtained are in favor of our previous assumption that Mg2+ may play its role by altering the physical state of the lipid bilayer, which would induce a conformational change in F0 (buried in the lipid core), which in turn is transmitted to the catalytic F1, resulting in a higher enzyme activity.

Altered expression of the H+ ATPase in Streptococcus faecalis membranes

Evidence is presented that expression of the H+ ATPase in S. faecalis is influenced by the extracellular pH and K+ level during growth. Altered expression was detected by assay of F1 ATPase and electrophoretic analysis of membrane proteins. K+-limited growth caused about a 2-fold increase in the F1 ATPase. The effect of growth at pH 6, 7 and 9 was studied. Compared to cells grown at pH 7, growth at pH 6 increased the F1 ATPase about 2-fold while growth at pH 9 reduced the F1 ATPase by nearly 4-fold. The elevated F1 ATPase activity in the pH 6 cells was associated with an increase in the F1 ATPase alpha and beta subunits in the membrane while the decrease in F1 ATPase in the pH 9 cells was associated with a marked loss of the alpha subunit. It is suggested that intracellular protons may act as effectors which regulate expression of the F1F0 gene cluster at the level of translation.

Role of Mg2+ in lipid-protein interaction in reconstituted procine heart mitochondrial H+-ATPase

During reconstitution of pig heart mitochondrial H+-ATPase in soybean phospholipid liposomes by the cholate dialysis method, Mg2+ greatly enhances 32Pi-ATP exchange activity, ATPase activity and the sensitivity to oligomycin of the reconstituted enzyme complex. The effect of Mg2+ on the fluidity of the reconstituted proteoliposomes was measured by means of a fluoursecent probe. 1-anilinonaphthalene ¿e-8-sulfonate, and spin-label probes, 5-nitroxide stearate, 12-nitroxide stearate and 16-nitroxide stearate. A difference in fluidity seems to be localized near the polar faces of the lipid bilayers of the reconstituted proteolipsomes. Fluidity was less in the presence of Mg2+ than it is absence. The conformations of the Mg2+-containing proteoliposomes was higher. We postulate that Mg2+ may play a role in altering the fluidity of the proteoliposomes, which would favor the formation of a conformation of the reconstituted H+-ATPase with higher activity.

Separation of odontoblast Ca2+-ATPase and alkaline phosphatase

Ca2+-ATPase activity was solubilized, partly purified, and separated from nonspecific alkaline phosphatase activity (APase1) of dentinogenically active rat incisor odontoblasts. Attempts were made to extract the enzymes by various agents, such as Triton X-100, deoxycholate, butanol, EDTA, and buffers of decreasing ionic strength. Solubilization by butanol followed by extraction with low concentrations of EDTA proved to be most effective. Purification and separation were done by molecular sieve chromatography. Ca2+-ATPase showed no activity against p-nitrophenyl phosphate (p-NPP) or inorganic pyrophosphate (PPi) and was unaffected by R 8231 [+/-)-6(m-bromophenyl)-5,6-dihydroimidazo(2,1-b)thiazole oxalate]. It was activated by Ca2+ and Mg2+ ions in equimolar concentrations with the substrate. The enzyme was rapidly inactivated in the solubilized state. An apparent molecular weight of about 18,000 was obtained from molecular sieve data. APase, showing activity against ATP, PPi, and p-NPP, was virtually totally inhibited by R 8231. It was activated by Mg2+ ions but slightly reduced in activity by Ca2+ ions. It had an apparent mol. wt. of 79,000. The results provide direct evidence for earlier suggestions of the existence in hard tissue forming cells of two phosphatases active at alkaline pH.

Site of ATPase activity in Myxococcus xanthus: lipid requirement for enzyme activity. Dedicated to Professor Dr. W. Schwartz on his 80th birthday

Treatment of cells with lysophosphatidylcholine, lysozyme, and phospholipase D removed most of their phospholipids and reduced ATPase activity to near zero. Addition of a microdispersion of phospholipids restored enzyme activity to various degrees. Phosphatidylcholine was most effective in reconstitution experiments, less effective were phosphatidylethanolamine and phosphatidylserine. Lipid analyses of cell fractions were possible through separation of cell wall and cell membrane in a sucrose gradient after differentiated treatment of glutaraldehyde fixed cells with lysophosphatidylcholine, lysozyme, and pronase. Phosphatidylcholine was almost exclusively a component of the cell membrane, whereas phosphatidylethanolamine was that of the wall. It is concluded that lipids are necessary for in vivo function of a Mg-dependent ATPase, and that membrane-associated phosphatidylcholine may serve as a matrix for the enzyme. Lipid extracts made from cells or cell fractions contained plasmologens, not previously reported to occur in Gram-negative, aerobic bacteria.

Energy conservation in chemotrophic anaerobic bacteria

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Properties and function of clostridial membrane ATPase

ATPase (ATP phosphohydrolase, EC 3.6.1.3) was detected in the membrane fraction of the strict anaerobic bacterium, Clostridium pasteurianum. About 70% of the total activity was found in the particulate fraction. The enzyme was Mg2+ dependent; Co2+ and Mn2+ but not Ca2+ could replace Mg2+ to some extent; the activation by Mg2+ was slightly antagonized by Ca2+. Even in the presence of Mg2+, Na+ or K+ had no stimulatory effect. The ATPase reaction was effectively inhibited by one of its products, ADP, and only slightly by the other product, inorganic phosphate. Of the nucleoside triphosphates tested ATP was hydrolyzed with highest affinity ([S]0.5 v = 1.3 mM) and maximal activity (120 U/g). The ATPase activity could be nearly completely solubilized by treatment of the membranes with 2 M LiCl in the absence of Mg2+. Solubilization, however, led to instability of the enzyme. The clostridial solubilized and membrane-bound ATPase showed different properties similar to the "allotopic" properties of mitochondrial and other bacterial ATPases. The membrane-bound ATPase in contrast to the soluble ATPase was sensitive to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). DCCD, at 10(-4) M, led to 80% inhibition of the membrane-bound enzyme; oligomycin ouabain, or NaN3 had no effect. The membrane-bound ATPase could not be stimulated by trypsin pretreatment. Since none of the mono- or divalent cations had any truly stimulatory effect, and since a pH gradient (interior alkaline), which was sensitive to the ATPase inhibitor DCCD, was maintained during growth of C. pasteurianum, it was concluded that the function of the clostridial ATPase was the same as that of the rather similar mitochondrial enzyme, namely H+ translocation. A H+-translocating, ATP-consuming ATPase appears to be intrinsic equipment of all prolaryotic cells and as such to be phylogenetically very old; in the course of evolution the enzyme might have been developed to a H+-(re)translocating, ATP-forming ATPase as probably realized in aerobic bacteria, mitochondria and chloroplasts.

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.

Solubilization of bacterial membrane proteins using alkyl glucosides and dioctanoyl phosphatidylcholine

The non-ionic detergent octyl glucoside solubilizes a substantial amount of Streptococcus faecalis membrane protein without loss of the monitored enzyme activities. A secondary detergent, dioctanoyl phophatidycholine, appears to increase the yield of solubilized material. In addition, the effect of ionic strength indicates that it may be possible to selectively extract groups of membrane proteins by their characteristic solubility at different ionic strengths. The solubilized membrane-associated enzymes, ATPase and NADH dehydrogenase, enter polyacrylamide gels as distict species. Electrophoretic studies suggest that there are two membrane-associated ATPase in the Streptococcus faecalis, one which dissociates from the membrane in the absence of Mg-2+ ions and the other which remains particulate until solubilized by detergents. Octyl glucoside can be easily removed from a solution containing solubilized proteins and lipid by dialysis.

The binding of deoxycholate, Triton X-100, sodium dodecyl sulfate, and phosphatidylcholine vesicles to cytochrome b5

Cytochrome b5 is composed of two domains that can be isolated after tryptic cleavage as two polypeptide fragments. One fragment is globular and hydrophilic and contains the heme; the other fragment is rich in hydrophobic amino acids and is essential for recombination of cytochrome b5 with microsomal membranes (Ito, A., and Sato, R. (1968), J. Biol. Chem. 243, 4922; Spatz, L., and Strittmatter, P. (1971), Proc. Nat. Acad. Sci. U.S. 68, 1042). Equilibrium dialysis and sedimentation equilibrium measurements of the binding of deoxycholate, Triton X-100 and dodecyl sulfate show that neither intact cytochrome b5 nor its proteolytic fragments possess high affinity binding sites for any of these amphiphiles. However, each detergent binds to the protein in a highly cooperative manner at concentrations near the critical micelle concentration. Binding measurements using the separated tryptic fragments show that deoxycholate and Triton X-100 (both nondenaturing detergents) bind to the hydrophobic fragment to the same extent as to intact cytochrome b5, and not at all to the polar fragment. Sodium dodecyl sulfate (a denaturing detergent) is bound to both tryptic fragments, but 70% of the detergent is bound to the hydrophobic fragment although it comprises only 30% of the protein mass. Less detailed measurements were made with synthetic and natural phosphatidylcholines, and show that the intact protein is quantitatively incorporated into phosphatidylcholine vesicles, but that no interaction with the polar fragment occurs. These results are interpreted in terms of the hydrophobic domain of cytochrome b5 having a diffuse hydrophobic surface that can act as a nonspecific nucleus for the formation of a micelle with a variety of amphiphilic substances. This domain of the molecule will insert into any available hydrophobic environment, whether it be detergent micelles, synthetic phospholipid vesicles, or the microsomal membrane. The incorporation of cytochrome b5 into the microsomal membrane is only a specialized case of the general property.

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.

Two classes of membrane binding of replicative RNA of bacteriophage MS2

Escherichia coli membranes were isolated in the presence of 6 mM Mg(++). They were washed with buffer containing no Mg(++) to yield a fraction containing material bound only in the presence of divalent cations, "membrane eluate," and that bound in the absence of divalent cations, "membrane." When E. coli infected with bacteriophage MS2 are labeled with [(14)C]uracil, all MS2 replicative RNA, i.e., the RNA species containing MS2 complementary RNA, is in the membrane eluate and membrane. The amount of [(14)C]uracil in replicative RNA found in the membrane eluate increases with time of labeling, whereas that in the replicative RNA in the membrane reaches a plateau in 1-2 min. This finding is consistent with a precursor-product relationship. Most of the label entering single-stranded viral RNA comes from the replicative RNA in the membrane eluate. This result suggests that polymerase components or factors required for complementary-strand synthesis are bound to membrane even in the absence of divalent cations and that the polymerase is no longer bound to these factors when it is making the bulk of the progeny single-stranded RNA.

Divalent cations in native and reaggregated mycoplasma membranes

The Mg(2+) content of membranes of several Mycoplasma and Acholeplasma species varied between 0.88 and 1.98 mug of Mg(2+) per mg of protein, depending on the species and on growth conditions. Ca(2+) could be detected only when it was added to the growth medium. The Mg(2+) content of isolated A. laidlawii membranes could be increased almost threefold by dialysis against 20 mm Mg(2+), whereas aggregated A. laidlawii membranes contained about six to eight times more Mg(2+) per mg of protein than the native membranes. This was taken to indicate that the molecular organization of the lipid and protein in the reaggregated membranes differs from that of the native membranes. Between 60 and 83% of the Mg(2+) in native and reaggregated A. laidlawii membranes was associated with the lipid fraction extracted with chloroform-methanol. The removal of over 80% of membrane protein by Pronase digestion did not release any significant amount of Mg(2+). Hence, most of the divalent cation appears to be bound to membrane lipids, most probably to phospholipids. Ethylenediaminetetraacetic acid released the bulk of Mg(2+) bound to the native and reaggregated A. laidlawii membranes, except for about 0.5 mug of Mg(2+) per mg of protein which was too tightly bound. Hence, a small but fairly constant amount of Mg(2+) is unavailable for chelation.

Reconstitution of Micrococcus lysodeikticus reduced nicotinamide adenine dinucleotide and L-malate dehydrogenases with dehydrogenase-depleted membrane residues: a basis for restoration of oxidase activities

Deoxycholate disruption of Micrococcus lysodeikticus protoplast membranes resulted in solubilization of both l-malate and reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase enzymes (substrate: 2,6-dichlorophenolindophenol oxidoreductases). Insoluble residues contained cytochromes of the b, c, and a type. Solubilized dehydrogenases were reconstituted with insoluble residues by treatment of disrupted membranes with magnesium ions. Most of the solubilized l-malate and NADH dehydrogenase activities were precipitated by magnesium ions independent of enzyme reconstitution with insoluble residues. Reconstituted dehydrogenases explained the mechanism for restoration of disrupted l-malate and NADH oxidase activities (4). Black light irradiation inhibited oxidase activities of both native and reconstituted membranes. These irradiated membrane oxidases were partially restored by exogenous napthoquinones [K(2(20)) and K(2(50))] but not by CoQ((6)). Reconstitution experiments showed that native membrane napthoquinone was retained in the insoluble residues of deoxycholate-disrupted membranes.