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1.
When a Euglena, in a medium containing ATP, is microinjected with 7 × 10?14 l of 0.02 M EDTA, which binds Ca2+ and Mg2+, flagellar motility stops. Flagellar arrest in Chlamydomonas occurs with the injection of 2 × 10?14 l of 0.02 M EDTA. The injection of similar amounts (7 × 10?14 l in Euglena and 3 × 10?14 l in Chlamydomonas) of 0.02 M EGTA, which preferentially binds Ca2+, did not significantly alter flagellar motility. This suggests that a decrease in the internal Ca2+ concentration in Euglena or Chlamydomonas did not stimulate flagellar beating. Further, flagellar motility decreased when internal Mg2+ was chelated. The microinjection of Zn2+ into these cells caused a decrease in flagellar frequency analogous to the decrease in frequency caused by the injection of Ca2+ and EDTA. The microinjection of 7 × 10?14 l of 0.2 M Mn2+ caused an approx. 1.5-fold increase in Euglena flagellar motility. Chlamydomonas flagella, which cease to beat upon impalement in an Mg2+-free medium, resume a flagellar frequency of 18 Hz when injected with 3 × 10?14 l of 0.2 M Mn2+. In the experiments reported here, Mn2+ acts as an analog of Mg2+. 相似文献
2.
When a Euglena, in a medium containing ATP, is microinjected with 7 × 10−14 l of 0.02 M EDTA, which binds Ca2+ and Mg2+, flagellar motility stops. Flagellar arrest in Chlamydomonas occurs with the injection of 2 × 10−14 l of 0.02 M EDTA. The injection of similar amounts (7 × 10−14 l in Euglena and 3 × 10−14 l in Chlamydomonas) of 0.02 M EGTA, which preferentially binds Ca2+, did not significantly alter flagellar motility. This suggests that a decrease in the internal Ca2+ concentration in Euglena or Chlamydomonas did not stimulate flagellar beating. Further, flagellar motility decreased when internal Mg2+ was chelated. The microinjection of Zn2+ into these cells caused a decrease in flagellar frequency analogous to the decrease in frequency caused by the injection of Ca2+ and EDTA. The microinjection of 7 × 10−14 l of 0.2 M Mn2+ caused an approx. 1.5-fold increase in Euglena flagellar motility. Chlamydomonas flagella, which cease to beat upon impalement in an Mg2+-free medium, resume a flagellar frequency of 18 Hz when injected with 3 × 10−14 l of 0.2 M Mn2+. In the experiments reported here, Mn2+ acts as an analog of Mg2+. 相似文献
3.
The ability of CASF (Ca2+-activated sarcoplasmic factor), a proteolytic enzyme that has recently been isolated from muscle and that removes Z-disks from myofibrils, to remove soluble material from myofibrils and to alter the Mg2+-modified ATPase activity of myofibrils was studied. A new assay involving determination of soluble material released from myofibrils was developed to measure CASF activity quantitatively. Optimum pH and optimum Ca2+ concentration for CASF activity as determined by this new assay were 7.0 and 1 mm, respectively. Proteolytic activity of CASF on myofibrils was prevented completely by excess EDTA. CASF treatment of myofibrils at CASF to myofibril ratios of 1: 20 by weight for 30 min caused a 20~25% increase in Mg2+-modified ATPase activity. CASF treatment for 360 min under these same conditions caused a decrease in Mg2+-modified ATPase activity at the highest ionic strengths used in this study (46.7 and 66.7 mm KCI). The increase in Mg2+-modified ATPase activity may originate from CASF degradation of troponin, whereas the decrease in Mg2+- modified ATPase activity may be due to CASF destruction or release of α-actinin from myofibrils. Digestion of myofibrils by CASF causes in the myofibrils (degradation of Z-lines, increase of ATPase activity) that are very similar to the changes caused by postmortem storage. 相似文献
4.
Depletion of Mg2+ in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by 3H-thymidine incorporation, and concomitant decreases in cellular K+ and Mg2+ and increases in Na+ and Ca2+. In cells grown in media containing 0.2 mM Ca2+, graded reduction of Mg2+ from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg2+. Concomitantly, cell cations showed graded changes, Na+ increasing to 227%, K+ decreasing to 52.5%, Mg2+ decreasing to 57.5% and Ca2+ increasing to 153.5% of control. The effects of Mg2+ depletion on DNA synthesis and cell cation content exhibited a dependence on Ca2+ concentration, the effects being larger at low Ca2+ concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg2+ caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg2+ depletion. The effects of Mg2+ depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg2+ concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg2+ in the coordinate control of growth and metabolism in animal cells. 相似文献
5.
The optimum Ca2+ concentration for growth of cotton (Gossypium hirsutum cv. Acala SJ-2) was in the range 1 to 15 mol m–3 for plants growing in hydroponic culture with 100–150 mol m–3 NaCl. Most saline (but not sodic) soils contain higher Ca2+ concentrations. CaCl2 was inhibitory to the growth of cotton above 20–50 mol m–3. Increasing concentrations of Ca2+ in the range 0–2 mol m–2 drastically reduced Na+ accumulation in the leaves. As CaCl2 concentrations were increased above the optimum for growth there was a further reduction in leaf Na+ accumulation, but this was more than offset by increased leaf Ca2+ and Cl– concentrations. Leaf K+ concentrations were not much affected by changes in external CaCl2 concentrations. The response of Mg2+ varied from an increase to a decrease with increasing external CaCl2 and was influenced by nutritional status. There was no evidence that high Ca2+ caused a deficiency of Mg2+ in cotton. Except for Cl–, whose concentrations tended to decrease initially and then increase as the CaCl2 concentration increased, the anions were largely unaffected by changes in external CaCl2. 相似文献
6.
Calcium,magnesium, and serum factors in multiplication of normal and transformed human lung fibroblasts 总被引:6,自引:0,他引:6
Wallace L. McKeehan Kerstin A. McKeehan 《In vitro cellular & developmental biology. Plant》1980,16(6):475-485
Summary Serum factors determine the extracellular requirement for both Ca2+ and Mg2+ for multiplication of normal human lung fibroblasts in vitro. Serum factors also affect the extracellular Ca2+ requirement for transformed fibroblasts but to a different extent than for normal cells. Transformed cells exhibit a reduced
requirement for both Ca2+ and Mg2+ for multiplication. The apparent reduction in Ca2+ requirement of transformed cells is dependent on the level of serum factors in the medium. The reduced Mg2+ requirement for transformed cells is more striking than the loss of Ca2+ and independent of the level of serum factors in the medium. A sequential effector relationship among serum factors, Ca2+ and Mg2+, in a proliferative control system for normal cells is proposed. Alteration or bypass of an intracellular Mg2+-requiring process is proposed as a major lesion in the transformed cells. This alteration causes an observed loss of requirements
for both Ca2+ and serum factors for the multiplication of transformed cells.
This work was supported by Grant CA-15305 from the National Cancer Institute, Contract 223-74-1156 from the Bureau of Biologics,
Food and Drug Administration, HEW Biomedical Research Support Grant S07RR05800, and the W. Alton Jones Foundation. 相似文献
7.
Yuyang Sun Senthil Selvaraj Archana Varma Susan Derry Abe E. Sahmoun Brij B. Singh 《The Journal of biological chemistry》2013,288(1):255-263
TRPM7 is a novel magnesium-nucleotide-regulated metal current (MagNuM) channel that is regulated by serum Mg2+ concentrations. Changes in Mg2+ concentration have been shown to alter cell proliferation in various cells; however, the mechanism and the ion channel(s) involved have not yet been identified. Here we demonstrate that TRPM7 is expressed in control and prostate cancer cells. Supplementation of intracellular Mg-ATP or addition of external 2-aminoethoxydiphenyl borate inhibited MagNuM currents. Furthermore, silencing of TRPM7 inhibited whereas overexpression of TRPM7 increased endogenous MagNuM currents, suggesting that these currents are dependent on TRPM7. Importantly, although an increase in the serum Ca2+/Mg2+ ratio facilitated Ca2+ influx in both control and prostate cancer cells, a significantly higher Ca2+ influx was observed in prostate cancer cells. TRPM7 expression was also increased in cancer cells, but its expression was not dependent on the Ca2+/Mg2+ ratio per se. Additionally, an increase in the extracellular Ca2+/Mg2+ ratio led to a significant increase in cell proliferation of prostate cancer cells when compared with control cells. Consistent with these results, age-matched prostate cancer patients also showed a subsequent increase in the Ca2+/Mg2+ ratio and TRPM7 expression. Altogether, we provide evidence that the TRPM7 channel has an important role in prostate cancer and have identified that the Ca2+/Mg2+ ratio could be essential for the initiation/progression of prostate cancer. 相似文献
8.
David M. Barnes Destiny B. Sykes James J. Smith David S. Miller 《Journal of cellular physiology》1995,164(2):304-314
The insulin mimic, peroxide of vanadate (pervanadate), stimulated 35S-methionine incorporation into Xenopus oocyte protein in a Mg2+-dependent manner. Reducing the extracellular Mg2+ concentration from 1.0 to 0.1 mM decreased the pervanadate-stimulated component of incorporation by 35%; with 0.01 mM Mg2+ or lower, the pervanadate-stimulated component was abolished. In addition, reducing extracellular Mg2+ to 0.01 mM inhibited about 50% of the insulinstimulated component of methionine incorporation. Mg2+ depletion had no effects on incorporation in controls or when protein synthesis was stimulated by Zn2+ or bovine growth hormone. Thus, not all substances that stimulated protein synthesis showed a dependence on extracellular Mg2+. Reducing extracellular Ca2+ had no effects on methionine incorporation in control cells or in cells stimulated by pervanadate or insulin. When oocytes maintained in a paraffin oil medium were brought into contact with a 0.5 m?I droplet of buffer containing the Mg2+ indicator dye, mag-fura-2, and pervanadate, apparent droplet Mg2+ decreased rapidly, indicating net uptake by the cells. Insulin also caused a net uptake of Mg2+. In contrast, apparent extracellular Mg2+ was constant when cells were in contact with droplets containing no effectors. Together, these data indicate that extracellular Mg2+, but not Ca2+, is involved in the stimulation of protein synthesis by pervanadate, and to a lesser extent by insulin. Pervanadate appears to induce a net uptake of Mg2+, and this change in membrane transport may be an early event in signalling the increase in translation. © 1995 Wiley-Liss, Inc. 相似文献
9.
1-adrenaline, ACTH and glucagon activate the adenylate cyclase of rat adipocytes by decreasing its S0.5(Mg2+) (concentration yielding 0.5 Vmax) from its basal value of 11.5 to 1.2, 0.3 and 1.8 mM and by increasing its Ki(ATP4?) from 0.03 to 0.25; 0.62 and 0.16 mM respectively. The kinetic properties of the enzyme are regulated by its state of saturation with ATP4? or Mg2+; its saturation with ATP4? and citrate3? suppressed its basal and hormone-dependent activities. The hormone-dependent decrease in Km and increase in Vmax of the enzyme occur when shifting from suboptimal low concentrations of hormone and Mg2+ to optimal conditions, i.e., high concentration of hormone and low concentration of Mg2+. The increase in the state of saturation of the enzyme with Mg2+ decreases the hormone-dependent effects on Vmax and results in identical values of Km (0.14 mM) for its basal and 1-adrenaline dependent activities. CaCl2 saturation curves at 5 mM ATP with either 5, 10 or 20 mM MgCl2 show that the substitution of 5 mM MgCl2 by 10 mM and 20 mM MgCl2 increased the Ki(Ca2+) of the enzyme from 0.19 to 0.49 and 0.94 mM but decreased its Ki(CaATP) from 0.42 to 0.19 and 0.14 mM respectively. Only when the concentration of MgCl2 exceeded that of ATP did 1-adrenaline and ACTH activate the enzyme by increasing its Ki(Ca2+), although only ACTH increased its Ki(CaATP). An increase in energy charge would decrease the intracellular concentrations of Mg2+ and Ca2+ because ATP4? has stronger binding constants for Mg2+ and Ca2+ than ADP3? and AMP2?. Hence, the reported properties of the enzyme suggests that changes in energy charge may allow for metabolic feedback control of the hormonal responsiveness of the Mg2+, Ca2+, ATP4? -sensitive adenylate cyclase. 相似文献
10.
Zenon Grabarek 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2011,1813(5):913-921
The Ca2+-binding helix-loop-helix structural motif called “EF-hand” is a common building block of a large family of proteins that function as intracellular Ca2+-receptors. These proteins respond specifically to micromolar concentrations of Ca2+ in the presence of ~1000-fold excess of the chemically similar divalent cation Mg2+. The intracellular free Mg2+ concentration is tightly controlled in a narrow range of 0.5-1.0 mM, which at the resting Ca2+ levels is sufficient to fully or partially saturate the Ca2+-binding sites of many EF-hand proteins. Thus, to convey Ca2+ signals, EF-hand proteins must respond differently to Ca2+ than to Mg2+. In this review the structural aspects of Mg2+ binding to EF-hand proteins are considered and interpreted in light of the recently proposed two-step Ca2+-binding mechanism (Grabarek, Z., J. Mol. Biol., 2005, 346, 1351). It is proposed that, due to stereochemical constraints imposed by the two-EF-hand domain structure, the smaller Mg2+ ion cannot engage the ligands of an EF-hand in the same way as Ca2+ and defaults to stabilizing the apo-like conformation of the EF-hand. It is proposed that Mg2+ plays an active role in the Ca2+-dependent regulation of cellular processes by stabilizing the “off state” of some EF-hand proteins, thereby facilitating switching off their respective target enzymes at the resting Ca2+ levels. Therefore, some pathological conditions attributed to Mg2+ deficiency might be related to excessive activation of underlying Ca2+-regulated cellular processes. This article is part of a Special Issue entitled: 11th European Symposium on Calcium. 相似文献
11.
《Micron and Microscopica Acta》1987,18(4):259-271
The effect of Ca2+ and Mg2+ on feline parathyroid cells during perfusion fixation with glutaraldehyde and subsequent immersion in OsO4 was investigated. Both Ca2+ and Mg2+ may exert a stabilizing or destabilizing effect on cell membranes and on elements of the cytoskeleton. The effect depends (1) on the ion concentration, (2) on the buffer concentration and (3) on the fixative. Stabilization due to Ca2+ or Mg2+ during glutaraldehyde fixation is not altered during subsequent osmication but both cations may cause destabilization during osmication in tissue prefixed without cations. Ca2+ and Mg2+ also reduce cell volume in combination with low osmolar buffer but they prevent cells from excessive shrinkage due to high osmolar buffers. Ca2+ and Mg2+ alone or in combination reduce swelling of RER, extraction of cellular material and loss of subcellular compartments, such as secretory granules, under optimal conditions. Ca2+, however, provokes formation of dark (shrunken) and light (swollen) cells accompanied by loss of subcellular components when used in low concentration during osmication. Low concentrations of Mg2+ added to glutaraldehyde exert similar effects. Stabilization of membranes is assumed to be due to the binding capacity of Ca2+ and Mg2+ to both phospholipids and proteins. The influence of Ca2+ and Mg2+ to changes in cell volume is considered likely to be the result of ionic interaction in the cytoplasmic gel, the maintenance of cell volume being a matter of equilibrium between the swelling pressure of the cytoplasmic gel and osmotic pressure of the fixative solution. 相似文献
12.
Peter Nygren 《Bioscience reports》1986,6(12):1057-1063
Monolayer culture of bovine parathyroid cells for 24 hours resulted in a right-shift of the dose-effect relationships for Ca2+-inhibition of parathyroid hormone (PTH) release and the dependence of the cytoplasmic Ca2+ concentration (Ca2+) on extracellular Ca2+ as well as in a less suppressible hormone release. After 4 days of culture, hormone secretion was almost non-suppressible and Ca
i
2+
increased poorly in response to a rise in extracelluiar Ca2+. Ionomycin, a Ca2+ ionophore, raised Ca
i
2+
, but there was only a small inhibition of PTH release and the correlation between Ca
i
2+
and secretion was weak. A deteriorated Ca
i
2+
regulation and a decreased inhibitory action of cytoplasmic Ca2+ on PTH release were also found in ceils from human parathyroid adenomas. Functional dedifferentiation of the parathyroid cell thus results from both defective regulation and action of cytoplasmic Ca2+. 相似文献
13.
《Molecular cell biology research communications》1999,1(3):221-226
It has been well established that increases in extracellular calcium concentration ([Ca2+]) inhibit parathyroid hormone (PTH) secretion. The effects of [Ca2+] are mediated through a G-protein-coupled receptor that has been cloned and characterized. Additionally, it has been demonstrated in parathyroid cells that an increase in [Ca2+] results in an increase in steady-state levels of intracellular calcium ([Ca2+]i). At present, it has not been fully resolved whether changes in [Ca2+]i are related to changes in PTH secretion. In the current study, the effect of increased [Ca2+] on PTH secretion and the connection regarding changes in concentrations of intracellular calcium [Ca2+]i have been examined in primary cultures of bovine parathyroid cells. PTH secretion was measured by radioimmunoassay and intracellular calcium was determined by single cell calcium imaging. Bovine parathyroid cells pre-incubated with either 0.5 or 1 mM calcium responded to rapid increases in [Ca2+] (≥0.5 mM) with an immediate and sustained increase in steady-state levels of [Ca2+]i that persisted for time intervals greater than 15 minutes. Although the magnitude of the sustained increase in [Ca2+]i varied among individual cells (∼40% to >300%), the overall pattern and course of time were similar in all cells examined (n = 142). In all trials, [Ca2+]i immediately returned to baseline levels following the addition of the calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Additional control studies, however, suggest that sustained increases in [Ca2+]i do not correlate with regulation of parathyroid hormone secretion. Sustained elevations of [Ca2+]i were not observed when [Ca2+] was gradually increased by the addition of 0.1 mM increments at 1 minute intervals. Furthermore, the effect on inhibition of PTH secretion was the same regardless of whether [Ca2+] was increased by gradual or rapid addition. 相似文献
14.
L. S. Krayushkina A. A. Panov A. A. Gerasimov W. T. W. Potts 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,165(7):527-533
During adaptation to brackish water the young great sturgeon Huso huso is able to regulate its serum osmolarity and ion concentrations. After transfer from fresh water to brackish water the ion concentrations in the urine increase and the urine becomes isoosmotic to the blood serum after 24h. The Na+ and K+ concentrations in the urine increase during the first 12 h by 4.4 and 7.7 times, respectively, later decreasing again. The Mg2+ and Ca2+ concentrations in the urine increase by 3.4 and 14 times during the first 72h in brackish water and remain high thereafter. These results suggest that the kidneys play an important part in the regulation of serum osmolarity and in the removal of Ca2+; however, in contrast to teleosts, Mg2+ must be removed extrarenally. During adaptation to a hyperosmotic medium the diameters of the Malpighian bodies, the glomeruli and the diameter of the tubules initially all decrease, but the distal tubules become morphologically differentiated into two regions and the diameter of the distal section later increases again. It is suggested that this is the site of Ca2+ secretion into the urine. 相似文献
15.
1. The enzymatic steps of the CO2 fixation cycle responsible for the overall inhibition of CO2 fixation caused by the lowering of the Mg2+ concentration in the stroma were investigated. For this the Mg2+ concentration in the stroma was decreased by addition of the ionophore A 23187, and the levels of the intermediates of the CO2 fixation cycle in the stroma of intact chloroplasts were assayed by ion exchange chromatography.2. The addition of the ionophore caused an increase of NADPH, ATP, fructose- and sedoheptulosebisphosphate and a dramatic decrease of phosphoglycerate in the stroma. These changes were reversed by the addition of Mg2+ and again affected by a subsequent addition of Ca2+. Ribulosebisphosphate and pentosemonophosphate levels in the stroma were only a little affected under these different conditions.3. The increase of the NADPH and ATP reflects the decreased utilization of these compounds due to the overall inhibition of CO2 fixation. As phosphoglycerate and triosephosphate appear to be in near equilibrium with NADPH and ATP, the decrease of phosphoglycerate seems to be a consequence of the changes in the nucleotide levels.4. The rapid increase of fructose- and sedoheptulosebisphosphate after the addition of the ionophore A 23187 clearly demonstrates that the overall inhibition of CO2 fixation caused by lowering the stromal Mg2+ is due to the inhibition of the hydrolysis of these sugar bisphosphates. It is concluded that the activities of fructose- and sedoheptulosebisphosphatase can be controlled by light dependent changes of the stromal Mg2+ concentration. 相似文献
16.
《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1988,968(2):253-260
When raising the extracellular Ca2+ concentration stepwise from 0.5 to 3.0 mM, bovine parathyroid cells reacted with initial transient and sustained elevations of the cytoplasmic Ca2+ concentration (Ca2+i), as well as more than 50% inhibition of parathyroid hormone (PTH) release. Human parathyroid adenoma cells and bovine cells cultured for 1 day or exposed to a low concentration of a monoclonal antiparathyroid antibody exhibited right-shifted dependencies of PTH release and Ca2+i on extracellular Ca2+ and reduced Ca2+i transients. The protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA) further right-shifted the dose response relationship for Ca2+ regulated Ca2+i of the adenoma cells, whereas the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) tended to normalize it, without affecting Ca2+i of normal bovine cells. In cells from an oxyphil adenoma and a parathyroid carcinoma as well as in bovine cells cultured 4 days or exposed to a high concentration of the antiparathyroid antibody, there were no Ca2+i transients, very small increases in steady-state Ca2+i and nonsuppressible PTH release. The results suggest that reduced availability of a putative Ca2+-receptor and increased protein kinase C activity may be important factors in the decreased Ca2+ sensitivity of abnormal parathyroid cells. 相似文献
17.
18.
P. E. Lindahl 《Experimental cell research》1973,81(2):413-431
Mg2+, Ca2+ and Mn2+ were found to act as activators of the ATP-dependent surface reaction, leading to head-to-head association in bull spermatozoa. Ca2+ was more efficient than Mg2+, while Zn2+, like Na+ + K+ in combination with Mg2+, seemed to have no such effect. High ionic strength induced head-to-head association, as did higher concentrations of Mg2+ and Ca2+ than those necessary for the activation of ATP, Ca2+ acting in a lower conc. than Mg2+. To this effect was added that of the ATP-dependent reaction when ATP was also present. As activators, Mg2+ and Ca2+ did not potentiate each other; their effects were cumulative when the ions acted together.When the ATP concentration within the range 1 × 10−5 to 8 × 10−5 M was increased stepwise in the presence of 2 × 10−5 M Mg2+ or Ca2+, the association resulting from each single concentration step progressively increased. At low cation concentrations, the increase was about the same for the two cations: at higher concentrations it was much steeper in the presence of Ca2+ than in that of Mg2+. In the latter case, it was not statistically significant above 4 × 10−5 M ATP.Increasing the cation concentration in the range 1 × 10−5 to 4 × 10−5 M in the presence of 2 × 10−5 M ATP produced an immediate high increase in association, which was followed by a lower increase. The optimum concentration ratio for Mg2+:ATP was at least 1:1 and for Ca2+: ATP at least 1.5:1.Oubain, containing enone structure, abolishes association. 相似文献
19.
Specific activity and Ca2+-affinity of (Ca2++Mg2+)ATPase of calmodulin-depleted ghosts progressively increase during preincubation with 0.1–2 mM Ca2+. Concomitantly, the increment in ATPase activity caused by calmodulin and the binding of calmodulin to ghosts decrease. The effects of calcium ions are abolished by the addition of calmodulin. ATP protects the enzyme from a Ca2+-dependent decrease of the maximum activity but does not seem to influence the Ca2+-dependent transformation of the low Ca2+-affinity enzyme into a high Ca2+-affinity form. 相似文献
20.
Specific activity and Ca2+-affinity of (Ca2++Mg2+)ATPase of calmodulin-depleted ghosts progressively increase during preincubation with 0.1–2 mM Ca2+. Concomitantly, the increment in ATPase activity caused by calmodulin and the binding of calmodulin to ghosts decrease. The effects of calcium ions are abolished by the addition of calmodulin. ATP protects the enzyme from a Ca2+-dependent decrease of the maximum activity but does not seem to influence the Ca2+-dependent transformation of the low Ca2+-affinity enzyme into a high Ca2+-affinity form. 相似文献