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1.
We have investigated the localization of a set of intrinsic ATPase activities associated with purified synaptic plasma membranes and consisting of (a) a Mg2+-ATPase; (b) an ATPase active at high concentrations of Ca2+ in the absence of Mg2+ (CaH-ATPase); (c) a Ca2+ requiring Mg2+-dependent ATPase (Ca + Mg)-ATPase, stimulated by calmodulin (Ca-CaM-ATPase); (d) a Ca2+-dependent ATPase stimulated by dopamine (DA-ATPase); and (e) the ouabain-sensitive (Na + K)-ATPase. The following results were obtained: (1) All ATPases are largely confined to the presynaptic membrane; (2) the DA-, (Ca + Mg)-, (Ca-CaM)-, and (Na + K)-ATPases are oriented with their ATP hydrolysis sites facing the synaptoplasm; (3) the Mg- and CaH-ATPases are oriented with their ATP hydrolysis sites on the junctional side of the presynaptic membrane and are therefore classified as ecto-ATPases of as yet unknown function.  相似文献   

2.
Vanadate inhibition of sarcoplasmic reticulum Ca2+-ATPase and other ATPases.   总被引:15,自引:0,他引:15  
Vanadate is a potent inhibitor of the Ca2+-ATPase activity of sarcoplasmic reticulum in the presence of A-23187. The purified enzyme is sensitive to vanadate even in the absence of the ionophore. Ca2+ and norepinephrine protect the enzyme against inhibition of vanadate. The nonspecificity of vanadate is emphasized by the finding of inhibition of several other ATPases including the Ca2+Mg2+-ATPases of the ascites and human red cell plasma membranes, Mg2+-ATPase of the ascites plasma membrane, and the K+-ATPases of E.coli and hog gastric mucosal cell membranes. The ascites plasma membrane Ca2+-ATPase (an ecto ATPase) and mitochondrial ATPase are not inhibited by vanadate.  相似文献   

3.
《Insect Biochemistry》1991,21(4):399-405
Na+,K+-activated ATPase activity in tick salivary glands increases during the rapid stage of tick feeding paralleling similar increases in dopamine and cAMP-stimulated fluid secretion. High concentrations of cyclic AMP increase Na+,K+-ATPase activity in a plasma membrane-enriched fraction from the salivary glands of rapidly feeding ticks. Cyclic AMP-dependent protein kinase inhibitor protein blocks activation of Na+,K+-ATPase activity at low but not high concentrations of cAMP indicating that both activator and inhibitor modulator phosphoproteins of Na+,K+-ATPase activity exist in the plasma membrane-enriched fraction.ATPase activity in the plasma membrane-enriched fraction is not measurable in the absence of Mg2+, Ca2+ and Na+. Ca-stimulated nucleotidase activity is highest with ATP serving as the preferred substrate in a series including CTP, UTP, GTP and ADP. Calcium, Mg2+ stimulated ATPase activity is activated further by calmodulin and partially inhibited by low concentration of vanadate, trifluoperazine and oligomycin. Results suggest that the plasma membrane-enriched fraction of tick salivary glands contains both Ca2+-ATPase activity and oligomycin-sensitive Ca2+, Mg2+-ATPase activities, the latter likely from a small amount of mitochondria in the partially purified organelle fraction.  相似文献   

4.
Antibodies raised in rabbits against the purified erythrocyte membrane Ca2+ pumping ATPase were affinity-purified using an ATPase-Sepharose column. Addition of a few molecules of the purified antibody per molecule of ATPase was sufficient to inhibit the ATPase activity. Extensively washed ghosts or preincubated pure ATPase sometimes develop an appreciable Mg2+-ATPase activity. In such cases, the antibodies inhibited the Mg2+-ATPase as well as the Ca2+-ATPase. This is consistent with the hypothesis that a portion of the Mg2+-ATPase activity of ghosts is derived from the Ca2+-ATPase. When nitrophenylphosphatase activity was observed, both Mg2+ - and Ca2+-stimulated activities were observed. Only the Ca2+ activity was inhibited by the antibodies, confirming that this activity is due to the Ca2+ pump, and suggesting that the Mg2+-nitrophenylphosphatase is due to a separate enzyme. Amounts of antibody comparable to those which inhibited the Ca2+-ATPases had no effect on the Na+-K+-ATPase; 4-fold higher amounts of antibody significantly stimulated the Na+-K+-ATPase, but this effect of the antibody was not specific: Immunoglobulins from the nonimmune serum also significantly stimulated the Na+-K+-ATPase.In resealed erythrocyte membranes, antibodies incorporated into the ghosts inactivated the Ca2+-ATPase, while antibodies added to the outside had no significant effect.  相似文献   

5.
Calcium is actively transported into intracellular organelles and out of the cytoplasm by Ca2+/Mg2+-ATPases located in the endoplasmic reticulum and plasma membranes. We studied the effects of aluminum on calcium transport in the adult rat brain. We examined 45Ca-uptake in microsomes and Ca2+-ATPase activity in microsomes and synaptosomes isolated from the frontal cortex and cerebellum of adult male Long-Evans rats. ATP-dependent45Ca-uptake was similar in microsomes from both brain regions. The addition of 50-800 μM AICI3 resulted in a concentration-dependent inhibition of 45Ca-uptake. Mg2+-dependent Ca2+-ATPase activity was significantly lower in synaptosomes compared to microsomes in both frontal cortex and cerebellum. In contrast to the uptake studies, AICI3 stimulated Mg2+-dependent Ca2+-ATPase activity in both microsomes and synaptosomes from both brain regions. To determine the relationship between aluminum and Mg2+, we measured ATPase activity in the presence of increasing concentrations of Mg2+ or AICI3. Maximal ATPase activity was obtained between 3 and 6 mM Mg2+. When we substituted AICI3 for Mg2+, ATPase activity was also stimulated in a concentration-dependent manner, but to a greater extent than with Mg2+. One interpretation of these data is that aluminum acts at multiple sites to displace both Mg2+ and Ca2+, increasing the activity of the Ca2+-ATPase, but disrupting transport of calcium.  相似文献   

6.
1. Homogenates of neural lobes of bovine pituitary glands were fractionated by differential and density-gradient ultracentrifugation and the distribution of adenosine triphosphatase (ATPase) activity was studied. It was shown that all the activity was membrane-bound. 2. On the basis of ionic requirements the ATPase activity was grouped into three categories: (a) Mg2+-dependent, (b) Ca2+-dependent and (c) Mg2++Na++K+-dependent (ouabain-sensitive) ATPases. The activity in the absence of bivalent cations was negligible. The ratio between the activities of the three ATPases varied between the different subcellular fractions. 3. Preincubation of the subcellular fractions with deoxycholate increased the activity of the Mg2++Na++K+-dependent enzyme, whereas the Mg2+- and Ca2+-activated ATPases were either unaffected or slightly inhibited. Triton X-100 solubilized the Mg2+- and Ca2+-ATPases; however, the activity of the Mg2++Na++K+-ATPase was abolished by the concentration of Triton X-100 used. 4. All the subfractions displayed unspecific nucleotide triphosphatase activity towards GTP, ITP and UTP. These substrates inhibited the hydrolysis of ATP by all three ATPases. ADP also inhibited the ATPases. 5. Polyacrylamide-gel electrophoresis of extracts containing the Mg2+- and Ca2+-dependent ATPase activity solubilized by Triton X-100 revealed the presence of two enzymes; one activated by either Mg2+ or Ca2+ and the other activated only by Ca2+. 6. In sucrose density gradients the distribution of vasopressin was different from that of all three types of ATPases. It is therefore suggested that the neurosecretory granules do not possess ATPase activity.  相似文献   

7.
The presence of an energy-dependent calcium uptake system in adipocyte endoplasmic reticulum (D. E. Bruns, J. M. McDonald, and L. Jarett, 1976, J. Biol. Chem.251, 7191–7197) suggested that this organelle might possess a calcium-stimulated transport ATPase. This report describes two types of ATPase activity in isolated microsomal vesicles: a nonspecific, divalent cation-stimulated ATPase (Mg2+-ATPase) of high specific activity, and a specific, calcium-dependent ATPase (Ca2+ + Mg2+-ATPase) of relatively low activity. Mg2+-ATPase activity was present in preparations of mitochondria and plasma membranes as well as microsomes, whereas the (Ca2+ + Mg2+)-ATPase activity appeared to be localized in the endoplasmic reticulum component of the microsomal fraction. Characterization of microsomal Mg2+-ATPase activity revealed apparent Km values of 115 μm for ATP, 333 μm for magnesium, and 200 μm for calcium. Maximum Mg2+-ATPase activity was obtained with no added calcium and 1 mm magnesium. Potassium was found to inhibit Mg2+-ATPase activity at concentrations greater than 100 mm. The energy of activation was calculated from Arrhenius plots to be 8.6 kcal/mol. Maximum activity of microsomal (Ca2+ + Mg2+)-ATPase was 13.7 nmol 32P/mg/min, which represented only 7% of the total ATPase activity. The enzyme was partially purified by treatment of the microsomes with 0.09% deoxycholic acid in 0.15 m KCl which increased the specific activity to 37.7 nmol 32P/mg/min. Characterization of (Ca2+ + Mg2+)-ATPase activity in this preparation revealed a biphasic dependence on ATP with a Hill coefficient of 0.80. The apparent Kms for magnesium and calcium were 125 and 0.6–1.2 μm, respectively. (Ca2+ + Mg2+)-ATPase activity was stimulated by potassium with an apparent Km of 10 mm and maximum activity reached at 100 mm potassium. The energy of activation was 21.5 kcal/mol. The kinetics and ionic requirements of (Ca2+ + Mg2+)-ATPase are similar to those of the (Ca2+ + Mg2+)-ATPase in sarcoplasmic reticulum. These results suggest that the (Ca2+ + Mg2+)-ATPase of adipocyte endoplasmic reticulum functions as a calcium transport enzyme.  相似文献   

8.
  • 1.1. Parotid plasma membrane nonpump low-affinity Ca2+-ATPase, which possesses high-affinity (Ca2+ + Mg2+ )-ATPase activity, was characterized.
  • 2.2. Purified Ca2+-ATPase hydrolyzed the nucleoside triphosphates, GTP, ITP, CTP, UTP, TTP (67–93% of ATP) and nucleoside diphosphates, ADP. GDP, IDP, CDP, TDP (12–40% of ATP) but not AMP and p-NPP.
  • 3.3. The maximum activities of Ca2+- and (Ca2+ +Mg2+ )-ATPases were obtained in the presence of 1 mM and 0.13 μ M Ca2+, respectively.
  • 4.4. The Km values for Ca2+ in Ca2+- and (Ca2++ Mg2+ )-ATPases were 0.2 mM and 22 nM. respectively.
  • 5.5. The activities of both Ca2+- and (Ca2+ + Mg2+ )-ATPases were found in the right-side-out-vesicles obtained from the plasma membrane-rich fraction.
  • 6.6. These features suggest that Ca2+-ATPase is an ecto-Ca2+-dependent nucleoside triphosphatase.
  相似文献   

9.
The flagellar motion of impaled bull spermatozoa can be maintained by external ADP or ATP. The post-impalement flagellar frequency depends sharply on the external Mg2+ concentration. 0.3 mM Mg2+ is required for half-optimal activity with ADP, 0.05 mM Mg2+ with ATP as external power source. Mn2+ can substitute partially for Mg2+ as ionic co-factor. Ca2+ cannot substitute for Mg2+, and at concentrations above 0.5 mM it inhibits motility slightly. Zn2+ acts only as inhibitor of post-impalement flagellar activity, reducing it to zero at concentrations above 1 mM.  相似文献   

10.
Nucleotide-metabolizing enzymes play important roles in the regulation of intracellular and extracellular nucleotide levels. We studied ATPase activity in the nervous ganglia of Phyllocaulis soleiformis, a terrestrial slug. The ATPase was divalent cation-dependent, with a maximal rate for ATP hydrolysis at pH 6.0 and 7.2 in the presence of Ca2+ (5 mM). Mg2+-ATPase activity was only 26% of the activity observed in the presence of Ca2+ (5 mM). ZnCl2 (10 mM) produced a significant inhibition of 70%. Ca2+-ATPase activity was insensitive to the classical ATPase inhibitors ouabain, N-ethylmaleimide, orthovanadate and sodium azide. Levamisole, an inhibitor of alkaline phosphatase, was ineffective. Among nucleotides, ATP was the best substrate. The apparent Km (ATP) for Ca2+-ATPase was 348±84 μM ATP and the Vmax was 829±114 nmol Pi min−1 mg−1 protein. The P. soleiformis ganglial ATPase does not appear to fit clearly into any of the previously described types of Ca2+-ATPases.  相似文献   

11.
A S Bloom  C O Haavik  D Strehlow 《Life sciences》1978,23(13):1399-1404
The effect of (?)-Δ9-THC on the activities of Mg2+?, Na+?K+? and Mg2+Ca2+-ATPases were studied in mouse brain subcellular fractions. In vitrotreatment with Δ9-THC produced a dose dependent stimulation of Mg2+ ATPase in the crude mitochondrial fraction and its subfractions and a dose-related inhibition of this activity in the microsomal fraction. Na+-K+- and Mg2+-Ca2+-ATPase activities were inhibited in a dose-related manner in all subcellular fractions studied.  相似文献   

12.
13.
In order to gain some information regarding Ca2+-dependent ATPase, the enzyme was purified from cardiac sarcolemma and its properties were compared with Ca2+-ATPase activity of myosin purified from rat heart. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by Ca2+ but the maximal activation of Ca2+-dependent ATPase required 4 mM Ca2+ whereas that of myosin ATPase required 10 mM Ca2+. These ATPases were also activated by other divalent cations in the order of Ca2+ > Mn2+ > Sr2+ > Br2+ > Mg2+; however, there was a marked difference in the pattern of their activation by these cations. Unlike the myosin ATPase, the ATP hydrolysis by Ca2+-dependent ATPase was not activated by actin. The pH optima of Ca2+-dependent ATPase and myosin ATPase were 9.5 and 6.5 respectively. Na+ markedly inhibited Ca2+-dependent ATPase but had no effect on the myosin ATPase activity. N-ethylmaleimide inhibited Ca2+-dependent ATPase more than myosin ATPase whereas the inhibitory effect of vanadate was more on myosin ATPase than Ca2+-dependent ATPase. Both Ca2+-dependent ATPase and myosin ATPase were stimulated by K-EDTA and NH4-EDTA. When myofibrils were treated with trypsin and passed through columns similar to those used for purifying Ca2+-ATPase from sarcolemma, an enzyme with ATPase activity was obtained. This myofibrillar ATPase was maximally activated at 3–4 mM Ca2+ and 3 to 4 mM ATP like sarcolemmal Ca2+-dependent ATPase. K+ stimulated both ATPase activities in the absence of Ca2+ and inhibited in the presence of Ca2+. Both enzymes were inhibited by Na+, Mg2+, La3+, and azide similarly. However, Ca2+ ATPase from myofibrils showed three peptide bands in SDS polyacrylamide gel electrophoresis whereas Ca2+ ATPase from sarcolemma contained only two bands. Sarcolemmal Ca2+-ATPase had two affinity sites for ATP (0.012 mM and 0.23 mM) while myofibrillar Ca2+-ATPase had only one affinity site (0.34 mM). Myofibrillar Ca2+-ATPase was more sensitive to maleic anhydride and iodoacetamide than sarcolemmal Ca2+-ATPase. These observations suggest that Ca2+-dependent ATPase may be a myosin like protein in the heart sarcolemma and is unlikely to be a tryptic fragment of myosin present in the myofibrils.  相似文献   

14.
Neuronal ATPases comprise a wide variety of enzymes which are not uniformly distributed in different membrane preparations. Since purified vesicle fractions have Mg2+/Ca2+-ATPase, the purpose of the present study was to know whether such enzyme activities have a preferential concentration in a synaptic vesicle fraction in order to be used as markers for these organelles. Resorting to a procedure developed in this Institute, we fractionated the rat cerebral cortex by differential centrifugation following osmotic shock of a crude mitochondrial fraction and separated a purified synaptic vesicle fraction over discontinuous sucrose gradients. Mg2+/Ca2+-ATPase activities and ultrastructural studies of isolated fractions were carried out. It was observed that similar specific activities for Mg2+/Ca2+-ATPases were found in all fractions studied which contain synaptic vesicles and/or membranes. Although the present results confirm the presence of Mg2+ and Ca2+-ATPase activities in synaptic vesicles preparations, they do not favor the contention that Mg2+/Ca2+-ATPase is a good marker for synaptic vesicles.  相似文献   

15.
Trifluoperazine dihydrochloride-induced inhibition of calmodulin-activated Ca2+-ATPase and calmodulin-insensitive (Na+ + K+)- and Mg2+-ATPase activities of rat and human red cell lysates and their isolated membranes was studied. Trifluoperazine inhibited both calmodulin-sensitive and calmodulin-insensitive ATPase activities in these systems. The concentration of trifluoperazine required to produce 50% inhibition of calmodulin-sensitive Ca2+-ATPase was found to be slightly lower than that required to produce the same level of inhibition of other ATPase activities. Drug concentrations which inhibited calmodulin-sensitive ATPase completely, produced significant reduction in calmodulin-insensitive ATPases as well. The data presented in this report suggest that trifluoperazine is slightly selective towards calmodulin-sensitive Ca2+-ATPase but that it is also capable of inhibiting calmodulin-insensitive (Na+ + K+)-ATPase and Mg2+-ATPase activities of red cells at relatively low concentrations. Thus the action of the drug is not due entirely to its interaction with calmodulin-mediated processes, and trifluoperazine cannot be assumed to be a selective inhibitor of calmodulin interactions under all circumstances.  相似文献   

16.
Plant cells frequently and rapidly have to respond to environmental changes for survival. Regulation of transport and other energy-requiring processes in the plasmalemma of root cells is therefore one important aspect of the ecological adaptation of plants. Wheat (Triticum aestivum L. cv. Drabant) was grown hydroponically, with or without 50 nM benzyladenine in the medium, and plasma membranes from root cells of 8-day-old plants were prepared by aqueous polymer two-phase partitioning. The influence of Ca2+ and Mg2+ on the plasmalemma ATPase activities was investigated. The presence of benzyladenine during growth increased the ATPase activity, that dependent upon Ca2+ more than that elicited by Mg2+. As a general characteristic, ATP was the preferred substrate, but all nucleotide tri- and diphosphates could be accepted with activities in plasma membranes from control plants of 7-36% (Mg2+) and 40-86% (Ca2+) and in plasma membranes from benzyladenine-treated plants of 12-47% (Mg2+) and 53-102% (Ca2+) as compared with activities obtained with ATP. Nucleotidemonophosphates were not hydrolyzed by the preparations. In preparations from benzyladenine-treated plants one peak of Ca2+-ATPase at pH 5.2–5.6, with a tail from pH 6 and upwards, and one peak of Mg2+-ATPase at pH 6.0–6.5 were observed in the presence of EDTA in the assay media. In preparations from control plants, the addition of EDTA to the assays resulted in a wide optimum between pH 6 and 7 for Mg2+-ATPase and low Ca2+-ATPase activity with no influence of pH in the range 4.5 to 8. Analysis of the pH dependence in the presence of both Ca2+ and Mg2+ indicates that the control plants mainly contain Mg2+-ATPase corresponding to the proton pump. Preparations from benzyladenine-treated wheat roots show, in addition, activation by Ca2+, which, in the slightly alkaline pH range may correspond to a Ca2+-extruding (Ca2++ Mg2+)-ATPase. In the acidic range, the responses are more complicated: the Mg2+-ATPase is inhibited by vanadate, while the Ca2+-ATPase is insensitive, and benzyladenine added during growth influences the interaction between Ca2+ and Mg2+ in a way that parallels the effect of high salt medium.  相似文献   

17.
Summary The aim of this study was to provide further evidence for the existence of a nonmitochondrial bicarbonate-stimulated Mg2+-ATPase in brush border membranes derived from rat kidney cortex. A plasma membrane fraction rich in brush border microvilli and a mitochondrial fraction were isolated by differential centrifugation. Both fractions contain a Mg2+-ATPase activity which can be stimulated by bicarbonate. The two Mg2+-ATPases are stimulated likewise by chloride, bicarbonate, and sulfite or inhibited by oligomycin and aurovertin, though to different degrees. In contrast to these similarities, only the Mg2+-ATPase activity of the mitochondrial fraction is inhibited by atractyloside, a substance which blocks an adenine nucleotide translocator in the inner mitochondrial membrane. On the other hand, filipin, an antibiotic that complexes with cholesterol in the membranes inhibits exclusively the Mg2+-ATPase of the cholesterol-rich brush border membranes. Furthermore it could be demonstrated by the use of bromotetramisole, an inhibitor of alkaline phosphatase activity, that the Mg2+-ATPase activity in the membrane fraction is not due to the presence of the highly active alkaline phosphatase in these membranes. These results support the assumption that an intrinsic bicarbonate-stimulated Mg2+-ATPase is present in rat kidney brush border membranes.  相似文献   

18.
In contrast to everted mitochondrial inner membrane vesicles and eubacterial plasma membrane vesicles, the ATPase activity of chloroplast ATP synthase in thylakoid membranes is extremely low. Several treatments of thylakoids that unmask ATPase activity are known. Illumination of thylakoids that contain reduced ATP synthase (reduced thylakoids) promotes the hydrolysis of ATP in the dark. Incubation of thylakoids with trypsin can also elicit higher rates of ATPase activity. In this paper the properties of the ATPase activity of the ATP synthase in thylakoids treated with trypsin are compared with those of the ATPase activity in reduced thylakoids. The trypsin-treated membranes have significant ATPase activity in the presence of Ca2+, whereas the Ca2+-ATPase activity of reduced thylakoids is very low. The Mg2+-ATPase activity of the trypsinized thylakoids was only partially inhibited by the uncouplers, at concentrations that fully inhibit the ATPase activity of reduced membranes. Incubation of reduced thylakoids with ADP in Tris buffer prior to assay abolishes Mg2+-ATPase activity. The Mg2+-ATPase activity of trypsin-treated thylakoids was unaffected by incubation with ADP. Trypsin-treated membranes can make ATP at rates that are 75–80% of those of untreated thylakoids. The Mg2+-ATPase activity of trypsin-treated thylakoids is coupled to inward proton translocation and 10 mM sulfite stimulates both proton uptake and ATP hydrolysis. It is concluded that cleavage of the γ subunit of the ATP synthase by trypsin prevents inhibition of ATPase activity by the ε subunit, but only partially overcomes inhibition by Mg2+ and ADP during assay.  相似文献   

19.
Flagellar activity in the biflagellate chlorophyte Chlamydomonas reinhardtii is selectively inhibited by Ni2+ or by treatment with Ca2+-chelating agents. Inhibitions of swimming speed, geotaxis, phototaxis, and pattern swimming result from qualitative and quantitative losses in the activity of individual flagella and in the coordination of activity beween the 2 flagella of each cell. Addition of Ca2+ (a) prevents inhibition and (b) restores normal flagellar activity in inhibited cells. Mg2+ is partially effective in reversal of inhibition. Other ions do not cause similar inhibition or reversal of nickel inhibition. The characteristics of inhibition and reversal suggest that the prmary target for nickel is a component of the flagellar apparatus, and that this component uses Ca2+ to perform its normal function in the regulation of flagellar activity. A 2nd target for nickel is a Carequiring process specific to phototaxis (and not involved in the photophobic response).  相似文献   

20.
To further study the toxicity of cadmium in the euryhaline alga, Dunaliella bioculata, ATPase activity and Cd2+ interactions were investigated in this species.Ultracytochemical studies showed the presence of ATPase reaction after incubation with Ca2+ and Mg2+, on different cell structures, the cytoplasm, the nucleoplasm, the axoneme and the membrane of the flagellae. In the cytoplasm, the localization of the lead precipates suggests that they are associated with the endoplasmic reticulum.The in vitro measurement of enzyme activity in crude cell extracts obtained by a partial solubilization of deflagellated algae with Triton X100, revealed a high Mg2+ dependent pyrophosphatase activity, a weak Mg2+-ATPase and a Ca2+-ATPase (Km = 0.12 mM) which was little sensitive to vanadate. In these extracts, a Ca2+ dependent ATPase was detected at the level of a double band by a non-denaturing electrophoresis. The same activity was found in the supernatant of sonicated cells in the absence of detergent, which suggests that this ATPase could be a cytosolic enzyme.In plasma membrane fractions, vanadate-sensitive ATPase activity was measured. This reaction was activated either by Mg2+ at relatively low concentrations (Km = 150µm) or by Ca2 +, but required unusually high concentrations of this ion, 50–100 mM.The inhibitory effects of Cd2+ on Ca2+ ATPase activity in cell extracts were compared with those of other cations. The range of toxicity was: Zn2+ > Cd2+ > Cu2+ > La3+ > Co2+. For Cd2+, the IC50 was 42 µM. The nature of inhibition, though, mixed was for the most part competitive, since the competitive constant value (Ki = 7 µM) was lower than the non-competitive constant value (Ki = 35 µM).In plasma membrane fractions, ATPase activity showed a high sensitivity to the heavy metal. It was non-competitively inhibited by cadmium in a narrow range of micromolar concentrations.  相似文献   

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