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.     

二价金属离子对嵌有线粒体H~+-ATP酶的脂酶体不同层次脂质流动性的影响

本文报道用荧光偏振及顺磁共振两种方法研究Mg~(2+)及其它二价金属离子对嵌有H~+-ATP酶的脂酶体不同层次脂质流动性的影响。 (1)顺磁标记探剂5-、12-、16-氮氧基硬脂酸测定结果表明Mg~(2+)和其它二价金属离子都能降低膜脂双分子层表层的流动性。降低流动性的顺序为Mg~(2+)=Ca~(2+)>Sr~(2+)>Cd~(2+)。较深层脂则无明显变化。 (2)荧光探剂7-、12-(9-蒽酰)硬脂酸及16-(9-蒽酰)棕榈酸的测定结果也表明Mg~(2+)和其它二价金属离子降低了膜脂表层的流动性,尤以Mn~(2+)、Ca~(2+)降低流动性最显著,流动性降低的顺序为;Mn~(2+) Ca>Sr~(2+) Mg~(2+) Cd~(2+)。除Mn~(2+)、Ca~(2+)还能影响膜脂深层的流动性外,其它与对照无明显差异。     

Mg~(2+)对线粒体H~+-ATP酶的F_O在脂质体重建时的影响

线粒体ATP合成酶是由具有H~+转运活性的F_0亚基,可溶性的催化中心F_1和连接二者的致寡霉素敏感蛋白(OSCP)所组成. 将纯化的猪心线粒体H—ATP酶复合体的F_0亚基,用胆酸盐透析法在有Mg~(2+)和无Mg~(2+)条件下在大豆磷脂脂质体上重建得脂酶体(L·F_0).用探剂9-AA荧光淬灭法和电权法测定了两种脂酶体的质子转运活力.由两种方法所得的实验结果均表明,在透返介质中加入1mmolmg~(2+)条件下形成的脂酶体(L·F_0)+Mg~(2+)较无Mg~(2+)者的质子转运活性明显增加.前者的荧光强度变化较后者增加约30%;由电极法测得的质子转运的初速度,前者为5nmolH~+′sF_0,后者为3nmolH~+′s·nmolF_O,质子转运活性高约一倍.这进一步支持Mg~(2+)通过调节脂的物理状态而诱导F_O具有较适合的构象,并进而将这一影响传递至F_1,使整个H~+—AhP酶具有较高活性的假设.     

Energy-linked reactions catalyzed by the purified ATPase complex (F0F1) from Rhodospirillum rubrum chromatophores

1. The isolation of F0F1-ATPase complex from Rhodospirillum rubrum chromatophores by the use of taurodeoxycholate is described. 2. The enzyme preparation contains about 12 polypeptides; five are subunits of the F1 moiety. 3. The ATPase activity of the purified enzyme is dependent on the addition of phospholipids. 4. Km-vales for Mg2+-ATP and Ca2+-ATP are similar to the values obtained for the membrane-bound enzyme. 5. The F0F1-ATPase complex is more than 70% inhibited by oligomycin and N,N'-dicyclohexylcarbodiimide. 6. The F0F1-ATPase complex was integrated into liposomes. The reconstituted proteoliposomes catalyzed energy transduction as shown by ATP-dependent quenching of acridine dye fluorescence and ATP-32Pi exchange.     

Binding of Mg2+ to the beta subunit or F1 of H+-ATPase from Escherichia coli

The bindings of Mg2+ to the F1 portion of Escherichia coli H+-ATPase and its isolated alpha and beta subunits were studied with 8-anilinonaphthalene-1-sulfonate (ANS). The fluorescence of ANS increased upon addition of F1 or its alpha subunit or beta subunit, as reported previously (M. Hirano, K. Takeda, H. Kanazawa, and M. Futai (1984) Biochemistry 23, 1652-1656). The fluorescence of ANS bound to F1 or its beta subunit increased significantly with further addition of Mg2+, whereas that of the alpha subunit increased only slightly. Ca2+ and Mn2+ had similar effects on the fluorescence of ANS with F1 and its beta subunit. The Mg2+-induced fluorescence enhancement (delta F) was high at an alkaline pH and was lowered by addition of ethylenediaminetetraacetic acid. Dicyclohexylcarbodiimide and azide had no effect on the delta F. Binding analysis showed that the concentration dependence of Mg2+ on the fluorescence enhancement of the beta subunit is similar to that of F1. These results suggest that both the beta subunit and F1 have binding sites for Mg2+ and that the delta F observed with F1 may be due to the binding of Mg2+ to the beta subunit.     

Ca~(2+)通过膜脂影响肌质网Ca~(2+)-ATP酶的活性与Ca~(2+)转运功能

重建在大豆磷脂脂质体上的兔骨骼肌肌质网Ca~(2+)—ATP酶在ATP驱动下可将溶液中的Ca~(2+)转运到脂酶体内部;外加EGTA则可除去脂酶体外部的Ca~(2+),由此可得到四种含Ca~(2+)状态不同的脂酶体:(1)内、外都无Ca~(2+);(2)仅外部有Ca~(2+);(3)内、外都有Ca~(2+);(4),仅内部有Ca~(2+).用DPH和AS系列萤光探针对这四种含Ca~+状态不同的脂酶体的膜脂流动性进行了测定,结果表明:脂酶体外部加入Ca~(2+),脂双层外表面的流动性降低.当Ca~(2+)进入脂酶体内部后,内表面膜脂的流动性也降低,而且外层膜脂流动性进一步降低.脂酶体内、外的Ca~(2+)含量不同时,Ca~(2+)—ATP酶功能状态也不同.转运到脂酶体内部的ca~(2+)积累到一定浓度后,通过Ca~(2+)泵向内转运的Ca~(2+)及Ca~(2+)—ATP酶活力都受到了抑制.转运进行到第四分钟时的酶活只有第一分钟的9%.但在相同的实验条件下,失去了完整的膜结构的纯化的Ca~(2+)—ATP酶蛋白没有被抑制.这提示完整的膜结构是这种抑制作用所必需的,而且膜两侧Ca~(2+)浓度的梯差可通过影响膜脂来调节Ca~(2+)—ATP酶的功能.     

Specificity of acidic phospholipids (CL & PA) in the activation of mitochondrial F0F1 ATPase by Mg2+

The interaction of Mg2+ with native F0F1 ATPase was studied. The hydrolytic activity of F0F1 ATPase could be competitively activated by Mg2+, but the preincubation of F0F1 ATPase with cholate eliminated the Mg2+ effect. The result from the comparison of the effect of Mg2+ on F0F1 ATPase with that on soluble F1 ATPase, and the fact that the activation of Mg2+ on cholate-treated F0F1 ATPase could be reconstituted only by divalent acidic phospholipid cardiolipin, indicate that there exists a specificity between the acidic phospholipids of the mitochondrial inner membrane and Mg2+ enhancement of ATP-hydrolyzing activity of F0F1 ATPase.     

Regulation of the skeletal sarcoplasmic reticulum Ca2+-ATPase by phospholamban and negatively charged phospholipids in reconstituted phospholipid vesicles

The Ca²⁺-ATPase of skeletal sarcoplasmic reticulum was purified and reconstituted in proteoliposomes containing phosphatidylcholine (PC). When reconstitution occurred in the presence of PC and the acidic phospholipids, phosphatidylserine (PS) or phosphatidylinositol phosphate (PIP), the Ca²⁺-uptake and Ca²⁺-ATPase activities were significantly increased (2–3 fold). The highest activation was obtained at a 50:50 molar ratio of PSYC and at a 10:90 molar ratio of PIP:PC. The skeletal SR Ca²⁺-ATPase, reconstituted into either PC or PC:PS proteoliposomes, was also found to be regulated by exogenous phospholamban (PLB), which is a regulatory protein specific for cardiac, slow-twitch skeletal, and smooth muscles. Inclusion of PLB into the proteoliposomes was associated with significant inhibition of the initial rates of Ca²⁺-uptake, while phosphorylation of PLB by the catalytic subunit of cAMP-dependent protein kinase reversed the inhibitory effects. The effects of PLB on the reconstituted Ca²⁺-ATPase were similar in either PC or PC: PS proteoliposomes, indicating that inclusion of negatively charged phospholipid may not affect the interaction of PLB with the skeletal SR Ca²⁺-ATPase. Regulation of the Ca²⁺-ATPase appeared to involve binding with the hydrophilic portion of phospholamban, as evidenced by crosslinking experiments, using a synthetic peptide which corresponded to amino acids 1–25 of phospholamban. These findings suggest that the fast-twitch isoform of the SR Ca²⁺-ATPase may be also regulated by phospholamban although this regulator is not expressed in fast-twitch skeletal muscles.     

Purification of Na+,K+-ATPase expressed in Pichia pastoris reveals an essential role of phospholipid-protein interactions

Na+,K+-ATPase (porcine alpha/his10-beta) has been expressed in Pichia Pastoris, solubilized in n-dodecyl-beta-maltoside and purified to 70-80% purity by nickel-nitrilotriacetic acid chromatography combined with size exclusion chromatography. The recombinant protein is inactive if the purification is done without added phospholipids. The neutral phospholipid, dioleoylphosphatidylcholine, preserves Na+,K+-ATPase activity of protein prepared in a Na+-containing medium, but activity is lost in a K+-containing medium. By contrast, the acid phospholipid, dioleoylphosphatidylserine, preserves activity in either Na+- or K+-containing media. In optimal conditions activity is preserved for about 2 weeks at 0 degrees C. Both recombinant Na+,K+-ATPase and native pig kidney Na+,K+-ATPase, dissolved in n-dodecyl-beta-maltoside, appear to be mainly stable monomers (alpha/beta) as judged by size exclusion chromatography and sedimentation velocity. Na+,K+-ATPase activities at 37 degrees C of the size exclusion chromatography-purified recombinant and renal Na+,K+-ATPase are comparable but are lower than that of membrane-bound renal Na+,K+-ATPase. The beta subunit is expressed in Pichia Pastoris as two lightly glycosylated polypeptides and is quantitatively deglycosylated by endoglycosidase-H at 0 degrees C, to a single polypeptide. Deglycosylation inactivates Na+,K+-ATPase prepared with dioleoylphosphatidylcholine, whereas dioleoylphosphatidylserine protects after deglycosylation, and Na+,K+-ATPase activity is preserved. This work demonstrates an essential role of phospholipid interactions with Na+,K+-ATPase, including a direct interaction of dioleoylphosphatidylserine, and possibly another interaction of either the neutral or acid phospholipid. Additional lipid effects are likely. A role for the beta subunit in stabilizing conformations of Na+,K+-ATPase (or H+,K+-ATPase) with occluded K+ ions can also be inferred. Purified recombinant Na+,K+-ATPase could become an important experimental tool for various purposes, including, hopefully, structural work.     

Direct evidence for the cytoplasmic location of the NH2- and COOH-terminal ends of the Neurospora crassa plasma membrane H+-ATPase

Reconstituted proteoliposomes containing Neurospora plasma membrane H+-ATPase molecules oriented predominantly with their cytoplasmic portion facing outward have been used to determine the location of the NH2 and COOH termini of the H+-ATPase relative to the lipid bilayer. Treatment of the proteoliposomes with trypsin in the presence of the H+-ATPase ligands Mg2+, ATP, and vanadate produces approximately 97-, 95-, and 88-kDa truncated forms of the H+-ATPase similar to those already known to result from cleavage at Lys24, Lys36, and Arg73 at the NH2-terminal end of the molecule. These results establish that the NH2-terminal end of the H+-ATPase polypeptide chain is located on the cytoplasmic side of the membrane. Treatment of the same proteoliposome preparation with trypsin in the absence of ligands releases approximately 50 water-soluble peptides from the proteoliposomes. Separation of the released peptides by high performance liquid chromatography and spectral analysis of the purified peptides identified only a few peptides with the properties expected of a COOH-terminal, tryptic undecapeptide with the sequence SLEDFVVSLQR, and NH2-terminal amino acid sequence analysis identified this peptide among the possible candidates. Quantitative considerations indicate that this peptide must have come from H+-ATPase molecules oriented with their cytoplasmic portion facing outward, and could not have originated from a minor population of H+-ATPase molecules of reverse orientation. These results directly establish that the COOH-terminal end of the H+-ATPase is also located on the cytoplasmic side of the membrane. These findings are important for elucidating the topography of the membrane-bound H+-ATPase and are possibly relevant to the topography of other aspartyl-phosphoryl-enzyme intermediate ATPases as well.     

Mn~(2+)和Cu~(2+)与脂质体和脂酶体相互作用的ESR研究

用ESR实验研究了Mn~(2 )、Cu~(2 )与DOPC,DPPC,SPL,DOPA,DPPA脂质体及其与H~ -ATP酶复合体重组的脂酶体的相互作用.通过Mn~(2 )—ESR谱线强度以及Cu~(2 )—ESR谱g因子的测量得出,磷脂分子头部不同的化学组成及其脂酰链的不同状态决定了Mn~(2 )、Cu~(2 )与膜脂结合的强弱程度,通过脂质体和脂酶体中自旋标记物5NS—ESR谱的测量进一步得出Mn~(2 )的结合增大了膜脂排列的序参数,而酶复合体的嵌入都导致与膜脂结合的Mn~(2 )比例减小.因而,当Mn~(2 )与脂酶体相互作用时,膜脂的排列最终达到一个平衡状态.在中性磷脂脂酶体的膜与Mn~(2 )之间,这种相互作用不明显.     

The role of phospholipids in the modulation of enzyme activities in the chromaffin granule membrane

(1) 93% of protein of chromaffin granule membranes can be solubilized by 1.3% (w/v) sodium cholate. The solubilized material can be substantially delipidated by ammonium sulphate precipitation. After three such cycles less than 2% of the endogenous phospholipids remain. (2) The chromaffin granule membrane Mg2+-ATPase depends on the presence of phospholipids for retention of its full activity. Soybean and extracted chromaffin granule phospholipids fully reactivate the delipidated enzyme provided only one delipidation step is used. (3) Successive ammonium sulphate precipitation steps result in a delipidated, and deactivated ATPase preparation which can be only partially reactivated on re-addition of phospholipids. (4) The phospholipid specificity for reactivation of the Mg2+-ATPase is broad. Although acidic phospholipids allow higher activities than neutral phospholipids, the main requirement appears to be the hydrophobic environment provided by the phospholipid hydrocarbon chains. (5) Correlations between changes in slope in the Arrhenius plot of the Mg2+-ATPase, and phase transitions in the phospholipid used for reactivation suggest that the 'fluidity' of the hydrocarbon chains modulates the activity of the enzyme.     

Reconstitution of sodium channels in large liposomes formed by the addition of acidic phospholipids and freeze-thaw sonication

Phosphatidylcholine (PC) alone or with phosphatidylethanolamine (PE) are sufficient for the reconstitution of Na+ channels in planar lipid bilayers. However, when Na+ channels were first reconstituted into liposomes using the freeze-thaw-sonication method, addition of acidic phospholipids, such as phosphatidylserine (PS), to the neutral phospholipids was necessary to obtain a significant toxin-modulated 22Na uptake. To further investigate the acidic phospholipid effect on reconstitution into liposomes, Na+ channels purified from Electrophorus electricus electrocytes were reconstituted into liposomes of different composition by freeze-thaw sonication and the effect of batrachotoxin and tetrodotoxin on the 22Na flux was measured. The results revealed that, under our experimental conditions, the presence of an acidic phospholipid was also necessary to obtain a significant neurotoxin-modulated 22Na influx. Though neurotoxin-modulated 22Na fluxes have been reported in proteoliposomes made with purified Na+ channels and PC alone, the 22Na fluxes were smaller than those found using lipid mixtures containing acidic phospholipids. Electron microscopy of negatively stained proteoliposomes prepared with PC, PC/PS (1:1 molar ratio), and PS revealed that the acidic phospholipid increases the size of the reconstituted proteoliposomes. The increment in size caused by the acidic phospholipid, due to the associated increase in internal volume for 22Na uptake and in area for Na+ channel incorporation, appears to be responsible for the large neurotoxin-modulated 22Na fluxes observed.     

Characterization of (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum by laser-excited europium luminescence

The molecular environment of Ca2+ translocating sites of skeletal muscle sarcoplasmic reticulum (SR) (Ca2+ + Mg2+)-ATPase has been studied by pulsed-laser excited luminescence of Eu3+ used as a Ca2+ analogue. Interaction of Eu3+ with SR was characterized by investigating its effect on partial reactions of the Ca2+ transport cycle. In native SR vesicles, Eu3+ was found to inhibit Ca2+ binding, phosphoenzyme formation, ATP hydrolysis activity and Ca2+ uptake in parallel fashion. The non-specific binding of Eu3+ to acidic phospholipids associated with the enzyme was prevented by purifying (Ca2+ + Mg2+)-ATPase and exchanging the endogenous lipids with a neutral phospholipid, dioleoylglycerophosphocholine. The results demonstrate that the observed inhibition of Ca2+ transport by Eu3+ is due to its binding to Ca2+ translocating sites. The 7F0----5D0 transition of Eu3+ bound to these sites was monitored. The non-Lorentzian nature of the excitation profile and a double-exponential fluorescence decay revealed the heterogeneity of the two sites. Measurement of fluorescence decay rates in H2O/D2O mixture buffers further distinguished the sites. The number of water molecules in the first co-ordination sphere of Eu3+ bound at transport sites were found to be 4 and 1.5. Addition of ATP reduced these numbers to zero and 0.6. These data show that the calcium ions in translocating sites are well enclosed by protein ligands and are further occluded down to zero or one water molecule of solvation during the transport process.     

The thermodynamic essence of the reversible inactivation of Na+/K+-transporting ATPase by various digitalis derivatives is relaxation of enzyme conformational energy

This paper reports on the kinetic and thermodynamic parameters describing the interaction of selected digitalis derivatives with hog and guinea-pig cardiac (Na+ + K+)-ATPase (Na+/K+-transporting ATPase EC 3.6.1.37). 32 digitalis derivatives were characterized as to the values of the delta G0', delta G----not equal to, and delta G----not equal to quantities in their interaction with (Na+ + K+)-ATPase from hog cardiac muscle in the presence of ATP, Mg2+, Na+ and K+. Nine derivatives were additionally characterized as to the values of the delta H0', delta S0', delta H----not equal to, delta S----not equal to, delta H not equal to, and delta S not equal to quantities in their interaction with the hog enzyme promoted by ATP, Mg2+ and Na+ in the presence or absence of K+. The formation of the inhibitory complexes is in any case an endothermic, entropically driven process. The Gibbs energy barriers in the formation and dissociation of the complexes, delta G----not equal to and delta G----not equal to, are imposed by large, unfavourable delta H not equal to values. K+ decreases the delta G0' value by increasing the delta G----not equal to value more than the delta G----not equal to value. In comparison with hog (Na+ + K+)-ATPase, the interaction of three derivatives with guinea-pig cardiac enzyme in the presence of ATP, Mg2+, Na+ and K+ is characterized by lower delta G0' values caused by lower favourable delta S0' values, and is accompanied by lower delta G----not equal to values. The magnitude of the kinetic parameters and the characteristic of the thermodynamic quantities describing the interaction between various digitalis derivatives and (Na+ + K+)-ATPase, indicate the induction of substantial conformational changes in the enzyme protein. A large entropy gain in the enzyme protein, observed irrespective of enzyme origin and ligation, appears to be the common denominator of the inhibitory action of all digitalis derivatives studied, suggesting that the digitalis-elicited relaxation of high conformational energy (negentropy strain) of the enzyme protein is the thermodynamic essence of the reversible inactivation of (Na+ + K+)-ATPase.     

Mg~(2+)加强嵌有H~+-ATP酶脂酶体脂质分子的堆积(packing)

用亲脂性的灵敏的荧光MC 540标记在有Mg~(2+)(1mM)与无Mg~(2+)条件下重建的线粒体H~+-ATP酶脂酶体,后者的荧光强度较前者增加30%左右.这提示,含Mg~(2+)的脂酶体的脂质分子间的堆积紧密度增加.在N-AF系列(n=27和16)探剂与MC 540之间的能量转移效率,又以反应靠近脂双层表面变化的2-AP与MC 54O之间最高.这进一步表明,含Mg~(2+)的脂酶体具有较适合流动性是与Mg~(2+)通过调节靠近脂双层表面的脂质分子具有适度的堆积相关的.这对阐明我们已提出的Mg~(2+)促进线粒体H~+-ATP酶重建作用模型进一步提供了较直接的证据.     

Reconstitution of the purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes into lipid vesicles and a characterization of the resulting proteoliposomes

The purified (Na+ + Mg2+)-ATPase from Acholeplasma laidlawii B membranes was reconstituted with dimyristoylphosphatidylcholine using a cholate solubilization and dialysis procedure. The incorporation of this enzyme into the phospholipid bilayer is accompanied by an enhancement of its specific activity and by a restoration of its lipid phase state-dependent properties which were lost during solubilization and purification from native membranes. Moreover, reconstitution of this ATPase with phospholipid also stabilizes it against cold inactivation at low temperatures (approximately equal to 0 degrees C), oxidative degradation at room temperature, and thermal denaturation at elevated temperatures (approximately equal to 55 degrees C). The elution profile from a Sepharose 4B-CL column indicates that all of the ATPase protein is associated with the phospholipid vesicles and that the Stoke's radius of the proteoliposomes formed is smaller than that of the lipid vesicles formed in the absence of any protein. The latter conclusion is supported by sedimentation velocity measurements and by an electron microscopic examination of negatively stained preparations. The electron microscopic studies demonstrate that sealed vesicles are formed only at low protein-to-lipid ratios. These observations indicate that the Acholeplasma laidlawii B (Na+ + Mg2+)-ATPase has been structurally and functionally reconstituted into lipid vesicles and that the proteoliposomes formed are amenable to studies aimed at the clarification of its proposed role as a sodium ion pump.     

The high affinity (Ca2+-Mg2+)-ATPase in liver plasma membranes is a Ca2+ pump. Reconstitution of the purified enzyme into phospholipid vesicles

The purified (Ca2+-Mg2+)-ATPase from rat liver plasma membranes (Lotersztajn, S., Hanoune, J., and Pecker, F. (1981) J. Biol. Chem. 256, 11209-11215) was incorporated into soybean phospholipid vesicles, together with its activator. In the presence of millimolar concentrations of Mg2+, the reconstituted proteoliposomes displayed a rapid, saturable, ATP-dependent Ca2+ uptake. Half-maximal Ca2+ uptake activity was observed at 13 +/- 3 nM free Ca2+, and the apparent Km for ATP was 16 +/- 6 microM. Ca2+ accumulated into proteoliposomes (2.8 +/- 0.2 nmol of Ca2+/mg of protein/90 s) was totally released upon addition of the Ca2+ ionophore A-23187. Ca2+ uptake into vesicles reconstituted with enzyme alone was stimulated 2-2.5-fold by the (Ca2+-Mg2+)-ATPase activator, added exogenously. The (Ca2+-Mg2+)-ATPase activity of the reconstituted vesicles, measured using the same assay conditions as for ATP-dependent Ca2+ uptake activity (e.g. in the presence of millimolar concentrations of Mg2+), was maximally activated by 20 nM free Ca2+, half-maximal activation occurring at 13 nM free Ca2+. The stoichiometry of Ca2+ transport versus ATP hydrolysis approximated 0.3. These results provide a direct demonstration that the high affinity (Ca2+-Mg2+)-ATPase identified in liver plasma membranes is responsible for Ca2+ transport.     

Rabbit platelet calcium ATPase differs from the human erythrocyte (Ca2+ + Mg2+)-ATPase in its response to three purified phospholipases A2, exogenous phospholipids and calmodulin

Human erythrocyte (Ca2+ + Mg2+)-ATPase and calcium ATPase of rabbit platelets were compared by their responses to a variety of treatments. These included three purified phospholipases A2 (acidic, neutral and basic) from Agkistrodon halys blomhoffii, as well as several phospholipids and lysophospholipids. The erythrocyte enzyme was stimulated 2-3-fold by all three phospholipases with maximal stimulation occurring at different concentrations of the three enzymes. The basic phospholipase was the most potent, followed by the neutral and acidic enzymes in that order. The calcium ATPase activity of the platelet was also stimulated by phospholipase treatment, but only by 10-20%. The stimulatory activity was attributable to hydrolysis of a very small portion of the total membrane phospholipid. Inactivation of the phospholipases by heating or chemical modification with p-bromophenacyl bromide abolished their ability to stimulate. Addition of polyphosphoinositides stimulated both ATPases. However, another acidic phospholipid, lysophosphatidic acid, stimulated only the erythrocyte enzyme and failed to affect the platelet calcium ATPase. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) had no effect on either enzyme, while the platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), its lyso compound and lysoPC inhibited both ATPases. Calmodulin stimulated the erythrocyte enzyme, but did not affect the platelet calcium ATPase. These results demonstrate that the protein-lipid interactions operative in the erythrocyte and platelet calcium ATPases are quite different.     

On the functional role of coupling factor B in the mitochondrial H+ -ATPase

Evidence for the presence of a functionally important vicinal dithiol in mitochondrial coupling factor B (FB) has been presented earlier (Sanadi, D. R. (1982) Biochim. Biophys. Acta 683, 39-56). FB was completely inactivated by 38 micron of copper o-phenanthroline or 0.63 mM iodosobenzoate, and the kinetics were consistent with intramolecular disulfide formation as were polyacrylamide gel patterns which showed that FB which had been treated with copper o-phenanthroline had a different mobility from that of untreated FB. ATP-Pi exchange activity and ATP-induced binding of bis[3-propyl-5-oxoisoxazol-4-yl]pentamethine oxonol (oxonol VI) to H+ -ATPase were also inhibited by the thiol oxidizing reagents, although oligomycin-sensitive ATPase activity was unaffected. F0 isolated from H+ -ATPase rebinds purified F1 with the restoration of ATP-induced oxonol-binding activity. Prior treatment of F0 (but not of F1) with copper o-phenanthroline abolished the oxonol-binding activity of reconstituted F0-F1. 115Cd binds tightly to H+ -ATPase and the bound protein can be recovered by gel electrophoresis in phosphate buffer in the presence of sodium dodecyl sulfate at a position corresponding to FB. Prior treatment of the H+ -ATPase with copper o-phenanthroline abolished 115Cd binding. The results indicate that the major effect of these inhibitors is on FB dithiol and leave little doubt that Cd2+ is indeed bound to a vicinal dithiol group.