Abbreviations: HEPES, N-2-hydroxyethylpiperazine-N′-ethanesulphonic acid; MES, 2-(N-morpholino)-ethanesulphonic acid 相似文献
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 prokaryotic 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. 相似文献
1. 1. A soluble, alkaline, Mg2+-dependent inorganic pyrophosphatase (EC 3.6.1.1) has been isolated from the stroma of intact spinach and pea chloroplasts and purified some 100-fold. The enzyme has a high specificity for inorganic pyrophosphate and Mg2+, and exhibits maximal activity at pH 8.2–8.6. The enzyme shows allosteric characteristics with Mg2+ as activator and optimal rates are obtained with a ratio of Mg2+ to PPi of approximately 4 to 1. The enzyme is inhibited by anionic PPi and by its own reaction product, orthophosphate.
2. 2. If Mg2+ is excluded from the medium in which isolated chloroplasts are assayed, active photosynthetic oxygen evolution can still be observed. The addition of Pi, but not PPi, will then offset a phosphate deficiency. If external Mg2+ is present PPi will also offset a phosphate deficiency and in these circumstances the rapidity and nature of the response is related to the external pyrophosphatase activity.
3. 3. Evidence is presented that the chloroplast envelope is relatively impermeable to PPi and that the response to added PPi is due to external hydrolysis followed by entry of Pi to the chloroplast. These results have significance concerning proposed mechanisms for control of photosynthesis.
(2) A light dependent increase in the Mg2+ content of the stroma was detected when chloroplasts were subjected to osmotic shock, amounting to 26 nmol/mg chlorophyll. Furthermore, a rapid and reversible light-dependent efflux of Mg2+ has been observed in intact chloroplasts when the divalent cation ionophore A 23 187 was added, indicating a light-dependent transfer of about 60 nmol of Mg2+ per mg chlorophyll from the thylakoid membranes to the stroma.
(3) CO2 fixation, but not phosphoglycerate reduction, could be completely inhibited when A 23 187 was added to intact chloroplasts in the absence of external Mg2+. If Mg2+ was then added to the medium, CO2 fixation was restored. Half of the maximal restoration was achieved with about 0.2 mM Mg2+, which is calculated to reflect a Mg2+ concentration in the stroma of 1.2 mM. The further addition of Ca2+ strongly inhibits CO2 fixation.
(4) The results suggest that illumination of intact chloroplasts causes an increase in the Mg2+ concentration of 1–3 mM in the stroma. Compared to the total Mg2+ content of chloroplasts, this increase is very low, but it appears to be high enough to have a possible function in the light regulation of CO2 fixation. 相似文献
The activity exhibited an absolute requirement for Mg2+ in the neutral pH range, while Ca2+ was found able to activate ATPase at more alkaline pH. Optimal activity was observed at pH 7.5, with a Mg/ATP ratio of 0.5.
ADP was found to inhibit ATP hydrolysis and to transform the Michaelian ATP concentration dependence with a Km of 0.5 mM into a sigmoid curve with increasing Km and decreasing V.
In contrast ADP activated an ATP-ADP exchange process and this shift from hydrolysis to exchange was stimulated by high Mg2+ and by orthophosphate.
All nucleoside triphosphates tested interfered with ATP hydrolysis, all could be hydrolyzed and could donate their terminal phosphate group to ADP. The relative efficiencies of nucleoside triphosphates in these three processes varied in parallel with minor discrepancies.
ATP hydrolysis was inhibited by N,N′-dicyclohexylcarbodiimide (DCCD) Dio 9, NaN3 and pyrophosphate, the first two being ineffective against ATP-ADP exchange, the third being stimulatory and the last inhibitory.
ATP hydrolysis and ATP-ADP exchange are tentatively attributed to the terminal enzyme of oxidative phosphorylation. 相似文献
The Mg2+-dependent or the (Mg2+ + Na+)-dependent phosphorylation of ADP by the phospho-protein (the exchange reaction) is reversibly inhibited when the microsomes are incubated with hydroxylamine.
The Na+-induced increment of 32P-labelling of microsomes previously incubated with [λ-32P]ATP is completely eliminated by hydroxylamine, but the Mg2+-dependent 32P-labelling of such microsomes is unaffected by hydroxylamine.
It is concluded that the phospho-enzyme formed during the Mg2+-dependent hydrolysis does not contribute to the Mg2+-dependent exchange reaction. Instead, the phosphoenzyme formed during the (Na+ + K+)-stimulated hydrolysis is apparently the only substance which phosphorylates ADP in the exchange reaction, even in the absence of Na+ and/or K+.
The hydroxylamine-sensitive nature of the sodium form of the phospho-enzyme in the (Na+ + K+)-stimulated ATPase sequence is consistent with the existence of an enzyme-acyl-phosphate bond of high internal energy with respect to that of ADP.
On the other hand, the hydroxylamine-resistant nature of the phospho-enzyme in the Mg2+-ATPase sequence suggests the existence of a non-acyl type of enzyme phosphate bond with low internal energy relative to that of ADP. 相似文献
The signal was seen only with intact, but not with broken, envelope-free chloroplasts, which had lost most of their divalent cations. This is interpreted to show that the indicator responds to an increase of Mg2+ concentration in the chloroplast stroma, which represents an efflux of Mg2+ from the intra-thylakoid space caused by light-dependent proton pumping.
As calculated from corrected values of the absorbance increase of Eriochrome Blue, the light-induced internal release of Mg2+ was close to 100 nequiv per mg chlorophyll at pH 7.6 and 250 nequiv at pH 7.1. This corresponds to a light-dependent increase in the concentration of free Mg2+ in the stroma of about 2 and 5 mM, respectively. 相似文献
1. 1. (Mg2+ + Ca2+) ATPases of microsomal and synaptic membrane preparations from immature and adult rat brain were activated by calcium (0.1–10 μM), maximal activation was found at 3 μM. The increase in (Mg2+ + Ca2+) ATPase seen during development was greatest in the synaptic membrane preparations.
2. 2. At 37°C both Na+ or K+ at concentrations higher than 30 mM inhibited the microsomal Mg2+ ATPase, but the (Mg2+ + Ca2+) ATPase was stimulated by both Na+ and K+. Synaptic membrane Mg2+ ATPase was inhibited by concentrations higher than 100 mM K+; Na+ however stimulated this enzyme at all concentrations. Much of this Na+ stimulated activity was ouabain sensitive. Synaptic membrane (Mg2+ + Ca2+) ATPase was stimulated by Na+ or K+, this stimulation follows approximate saturation kinetics with an apparent Km of 18.8 mM Na+ or K+.
3. 3. Arrhenius plots of microsomal (Mg2+ + Ca2+) ATPase were curvilinear, but two intersecting lines with a break at 20°C could be fitted. The calculated energies of activation from these lines were very similar in immature and adult preparations. The synaptic membrane preparation (adult) also gave a curvilinear plot; but two intersecting lines with a break at 25°C could be fitted to the data. These lines had slopes of 21 and 28 Kcal mole−1 above and below the break, respectively. The immature preparation when made using EDTA gave a Arrhenius plot of very similar form to the adult preparation. Without EDTA however the Arrhenius plot was complex with a plateau at 25–32°C. Pretreatment with EDTA activated the synaptic membrane (Mg2+ + Ca2+) ATPase from both immature and adult brain.
Author Keywords: Brain; ATPase; temperature; development; synaptic membranes 相似文献
异;低氧组甘肃鼢鼠SOD、CAT、GR、Ca2 + - ATP 酶、Ca2 + - Mg2 + - ATP 酶和Na + - K + - ATP 酶活性迅速升高,显著高于SD 大鼠,MDA 含量则显著低于SD 大鼠。说明甘肃鼢鼠心脏通过提高抗氧化酶活性清除低氧诱导产生的多余自由基,并通过提高ATP 酶活性保证心电活动正常、心率稳定,应对低氧应激。 相似文献
1. 1. The effect of the Mg2+ concentration on the CO2 fixation activity in situ in isolated and intact spinach chloroplasts upon suspension in hypotonic medium was examined. CO2 fixation in the dark was activated 25–100 fold by 20 mM Mg2+ in the presence of added ATP plus either ribulose 5-phosphate or ribose 5-phosphate. 20 mM Mg2+-stimulated fixation only 2–3 fold in the presence of the substrate of fixation, ribulose 1,5-diphosphate. The highest Mg2+-stimulated rate of fixation in the dark observed with chloroplasts was 480 μmoles CO2 fixed per mg chlorophyll per h.
2. 2. The concentration of bicarbonate at half of the maximal velocity (apparent Km) during the Mg2+-stimulated fixation of CO2 was 0.4 mM in the presence of ATP plus ribose 5-phosphate and 0.6 mM with ribulose 1,5-diphosphate.
3. 3. Dithioerythritol or light enhanced Mg2+-stimulated CO2 fixation 1–3 fold in the presence of ATP plus ribose 5-phosphate but not ribulose 1,5-diphosphate.
4. 4. These results indicate that Mg2+ fluxes in the stroma of the chloroplast could control the activity of the phosphoribulokinase with a lesser effect on the ribulosediphosphate carboxylase. An increase in Mg2+ of 6–10 mM in the stroma region of the chloroplast would be enough to activate CO2 fixation during photosynthesis.
Abbreviations: Rib-5-P, ribose 5-phosphate; Ribul-5-P, ribulose 5-phosphate; Ribul-1,5-P2, ribulose 1,5-diphosphate; HEPES, N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid; MES, 2-(N-morpholino)ethanesulfonic acid 相似文献
These results show that trypsin modifies the actin-myosin interaction in at least two ways: (1) a very rapid initial modification that increases the Mg2+ + Ca2+-modified ATPase activity and the rate of turbidity increase, and (2) a slower modification that decreases the Mg2+ + Ca2+-modified ATPase activity and rate of turbidity response, and that lengthens contracted sarcomeres. Tryptic modification is not due to cleavage of myosin to light and heavy meromyosin. Since tryptic modification occurs more rapidly than conversion of myosin to light and heavy meromyosin, all heavy meromyosin preparations will be modified. 相似文献
In accordance with the results of our previous study concerning the effects of Mg2+ on the excitation transfer in the chloroplasts, it was concluded that ions of alkaline earths and manganese suppress the excitation transfer from bulk chlorophylla of pigment system II to that of pigment system I. 相似文献
2. The ATPase is activated up to 18-fold by lysolecithin and to a smaller extent by cardiolipin, phosphatidylinositol and phosphatidylethanolamine. The amount required of each of these phospholipids to give half-maximal activation is apparently inversely related to the number of fatty acid chains in the lipid. Lecithin, which is a poor activator of the ATPase, competitively inhibits the activation by cardiolipin.
3. The activation of the ATPase consists of an increase in both the maximal velocity of the reaction and the affinity for substrate ATP. The pH optimum of the reaction is not influenced by the charge of the lipid.
4. Arrhenius plots of ATPase activated with lysolecithin show a transition to a higher activation energy at temperatures below 19 °C. The sensitivity of the lysolecithin-activated enzyme to oligomycin is markedly reduced below the same temperature. With cardiolipin the transition is observed at 13 °C.
5. ADP, Mg2+ and to a smaller extent ATP, Mg2+ enhance the activation of ATPase by suboptimal amounts of phospholipid. 相似文献
1. 1. It has been proposed that Mg2+, inorganic pyrophosphate and a protein fraction which exhibits fructose-1,6-diphosphatase activity may interact to regulate photosynthesis by isolated chloroplasts.
2. 2. Evidence is presented which confirms the interaction and regulation but shows that these effects are indirectly attributable to pyrophosphatase activity rather than fructose-1,6-diphosphatase.
3. 3. When provided with Mg2+ and PPi the pyrophosphatase simply alters the proportions of orthophosphate and PPi in the reaction mixture. As the Pi concentration is increased, it first stimulates and then inhibits, the degree of inhibition being enhanced by additional Mg2+. PPi ameliorates the inhibition, possibly by chelation of Mg2+.
4. 4. It is concluded that the proposed regulation is ultimately governed by the Pi concentration and the known relationship between Pi uptake and triose phosphate export across the chloroplast envelope.
Abbreviations: HEPES, N-2-hydroxyethylpiperazine-N′-ethanesulphonic acid; MES, 2-(N-morpholino)-ethanesulphonic acid 相似文献