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1.
A cDNA clone, called CLB1, was isolated from a cDNA library from tomato (Lycopersicon esculentum) and characterized. The CLB1 cDNA contains an open reading frame of 1518 bp, and encodes a putative protein of 506 amino acids with a predicted molecular mass of 54 633 Da. The deduced CLB1 amino acid sequence contains a domain that exhibits from 26% to 37% identity with the Ca2+-dependent lipid-binding domains of cytosolic phospholipase A2, protein kinase C, Rabphilin-3A, and Synaptotagmin I of animals. Southern blot analysis indicates that the CLB1 gene belongs to a small gene family in the tomato genome. The CLB1 mRNA is preferentially expressed in fruit tissues. 相似文献
2.
Elizabeth Zubrzycka-Gaarn Glen MacDonald Laurie Phillips Annelise O. Jorgensen David H. MacLennan 《Journal of bioenergetics and biomembranes》1984,16(5-6):441-464
In order to determine whether polymorphic forms of the Ca2+ + Mg2+-dependent ATPase exist, we have examined the cross-reactivity of five monoclonal antibodies prepared against the rabbit skeletal muscle sarcoplasmic reticulum enzyme with proteins from microsomal fractions isolated from a variety of muscle and nonmuscle tissues. All of the monoclonal antibodies cross-reacted in immunoblots against rat skeletal muscle Ca2+ + Mg2+-dependent ATPase but they cross-reacted differentially with the enzyme from chicken skeletal muscle. No cross-reactivity was observed with the Ca2+ + Mg2+-dependent ATPase of lobster skeletal muscle. The pattern of antibody cross-reactivity with a 100,000 dalton protein from sarcoplasmic reticulum and microsomes isolated from various muscle and nonmuscle tissues of rabbit demonstrated the presence of common epitopes in multiple polymorphic forms of the Ca2+ + Mg2+-dependent ATPase. One of the monoclonal antibodies prepared against the purified Ca2+ + Mg2+-dependent ATPase of rabbit skeletal muscle sarcoplasmic reticulum was found to cross-react with calsequestrin and with a series of other Ca2+-binding proteins and their proteolytic fragments. Its cross-reactivity was enhanced in the presence of EGTA and diminished in the presence of Ca2+. Its lack of cross-reactivity with proteins that do not bind Ca2+ suggests that it has specificity for antigenic determinants that make up the Ca2+-binding sites in several Ca2+-binding proteins including the Ca2+ + Mg2+-dependent ATPase.This paper is dedicated to the memory of Dr. David E. Green. 相似文献
3.
Two kinds of ATP binding sites were found on the ATPase molecule in deoxycholic acid-treated sarcoplasmic reticulum. One was the catalytic site (1 mol/mol active site) and its affinity was high. Upon addition of Ca2+, all the ATP bound to the catalytic site disappeared at 75 mM KCl, while a significant amount of ATP remained bound to the site at 0–2 mM KCl. The latter binding was found to be due to the formation of a slowly exchanging enzyme-ATP complex, which is in equilibrium with phosphoenzyme + ADP. The other binding site was the regulatory one (1 mol/mol active site) and its affinity was low, changing only insignificantly upon addition of Ca2+. The ATP binding to the regulatory site shifted the equilibrium between the slowly exchanging complex and EP toward EP. 相似文献
4.
Zoltan Olah Laszlo Bogre Csaba Lehel Anna Farago Janos Seprodi Denes Dudits 《Plant molecular biology》1989,12(4):453-461
A 50 kDa, calcium-dependent protein kinase (CDPK) was purified about 1000-fold from cultured cells of alfalfa (Medicago varia) on the basis of its histone H1 phosphorylation activity. The major polypeptide from bovine histone H1 phosphorylated by either animal protein kinase C (PK-C) or by the alfalfa CDPK gave an identical phosphopeptide pattern. The phosphoamino acid determination showed phosphorylation of serine residues in histone H1 by the plant enzyme. Histone-related oligopeptides known to be substrates for animal histone kinases also served as substrates for the alfalfa kinase. Both of the studied peptides (GKKRKRSRKA; AAASFKAKK) inhibited phosphorylation of H1 histones by bovine and alfalfa kinases. The results of competition studies with the nonapeptide (AAASFKAKK), which is a PK-C specific substrate, suggest common features in target recognition between the plant Ca2+-dependent kinase and animal protein kinase C. We also propose that synthetic peptides like AAASFKAKK can be used as a tool to study substrates of plant kinases in crude cell extracts. 相似文献
5.
Ca2+,Mg2+- and Ca2+,Mn2+-dependent and acid DNases were isolated from spermatozoa of the sea urchin Strongylocentrotus intermedius. The enzymes have been purified by successive chromatography on DEAE-cellulose, phenyl-Sepharose, Source 15Q, and by gel filtration, and the principal physicochemical and enzymatic properties of the purified enzymes were determined. Ca2+,Mg2+-dependent DNase (Ca,Mg-DNase) is a nuclear protein with molecular mass of 63 kD as the native form and its activity optimum is at pH 7.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca2+ + Mg2+) > Mn2+ = (Ca2+ + Mn2+) > (Mg2+ + EGTA) > Ca2+. Ca,Mg-DNase retains its maximal activity in sea water and is not inhibited by G-actin and N-ethylmaleimide, whereas Zn2+ inhibits the enzyme. The endogenous Ca,Mg-DNase is responsible for the internucleosomal cleavage of chromosomal DNA of spermatozoa. Ca2+,Mn2+-dependent DNase (Ca,Mn-DNase) has molecular mass of 25 kD as the native form and the activity optimum at pH 8.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca2+ + Mn2+) > (Ca2+ + Mg2+) > Mn2+ > (Mg2+ + EGTA). In seawater the enzyme is inactive. Zinc ions inhibit Ca,Mn-DNase. Acid DNase of spermatozoa (A-DNase) is not a nuclear protein, it has molecular mass of 37 kD as a native form and the activity optimum at pH 5.5, it is not activated by bivalent metal ions, and it is inhibited by N-ethylmaleimide and iodoacetic acid. Mechanisms of the endonuclease cleavage of double-stranded DNA have been established for the three enzymes. The possible involvement of DNases from sea urchin spermatozoa in programmed cell death is discussed. 相似文献
6.
Vincenzo Panagia Vijayan Elimban Pallab K. Ganguly Naranjan S. Dhalla 《Molecular and cellular biochemistry》1987,78(1):65-71
Heart sarcolemma has been shown to possess three catalytic sites (I, II and III) for methyl transferase activity (Panagia V, Ganguly PK and Dhalla NS. Biochim Biophys Acta 792: 245–253, 1984). In this study we examined the effect of phosphatidylethanolamine N-methylation on ATP-independent Ca2+ binding and ATPase activities in isolated rat heart sarcolemma. Both low affinity (1.25 mM Ca2+) and high affinity (50 µM Ca2+) Ca2+ binding activities were decreased following incubation of sarcolemmal membranes with AdoMet under optimal conditions for site II and III. Similarly, Ca2+ ATPase activities measured at 1.25 mM and 4 mM Ca2+ were depressed by phospholipid N-methylation. S-adenosyl homocysteine, a specific inhibitor of phospholipid N-methylation, prevented the depression of low affinity Ca2+ binding and Ca2+ ATPase activities, whereas the methylation-induced effect on the high affinity Ca2+ binding was not influenced by this agent. Pretreatment of sarcolemma with methyl acetimidate hydrochloride, an amino group blocking agent, also prevented the methylation-induced inhibition of both Ca2+ binding and Ca2+ ATPase. A further decrease in Ca2+ binding and Ca2+ ATPase activities together with a marked increase in the intramembranal level of PC was seen when membranes were methylated under the site III conditions in the presence of phosphatidyldimethylethanolamine as exogenous substrate. There was no effect of phospholipid methylation on sarcolemmal Na+-K+ ATPase and Mg2+ ATPase activities. These results indicate a role of phospholipid N-methylation in the regulation of sarcolemmal Ca2+ ATPase and low affinity ATP-independent Ca2+ binding. 相似文献
7.
The conformational states of Ca2+-ATPase in sarcoplasmic reticulum (SR) vesicles with or without a thousand-fold transmembrane Ca2+ gradient have been studied by fluorescence spectroscopy and fluorescence quenching. In consequence of the establishment of the transmembrane Ca2+ gradient, the steady-state fluorescence results revealed a reproducible 8% decrease in the intrinsic fluorescence while time-resolved fluorescence measurements showed that 13 tryptophan residues in SR · Ca2+-ATPase could be divided into three groups. The fluorescence lifetime of one of these groups increased from 5.5 ns to 5.95 ns in the presence of a Ca2+ gradient. Using KI and hypocrellin B (a photosensitive pigment obtained from a parasitic fungus, growing in Yunnan, China), the fluorescence quenching further indicated that the dynamic change of this tryptophan group, located at the protein-lipid interface, is a characteristic of transmembrane Ca2+ gradient-mediated conformational changes in SR · Ca2+-ATPase.Abbreviations SR
sarcoplasmic reticulum
- HB
hypocrellin B
- Trp
tryptophan
- DMSO
dimethysulfoxide
- Hepes
N-2-hydroxyethyl piperazine-N-ethanesulfonic acad
- SR(50005)
SR vesicles with 1000-fold transmembrane Ca2+ gradient
- SR(5050)
SR vesicles without Ca2+ gradient
- Ksv(app)
apparent Stern-Volmer constant
- Ksvi
Stern-Volmer constant of component i for dynamic quenching 相似文献
8.
Ligand binding to transport sites constitutes the initial step in the catalytic cycle of transport ATPases. Here, we consider the well characterized Ca2+ ATPase of sarcoplasmic reticulum (SERCA) and describe a series of Ca2+ binding isotherms obtained by equilibrium measurements in the presence of various H+ and Mg2+ concentrations. We subject the isotherms to statistical mechanics analysis, using a model based on a minimal number of mechanistic steps. The analysis allows satisfactory fits and yields information on occupancy of the specific Ca2+ sites under various conditions. It also provides a fundamental method for analysis of binding specificity to transport sites under equilibrium conditions that lead to tightly coupled catalytic activation. 相似文献
9.
Ca2+ is believed to be a critical second messenger in ABA signal transduction. Ca2+-dependent protein kinases (CDPKs) are the best characterized Ca2+ sensors in plants. Recently, we identified an Arabidopsis CDPK member CPK12 as a negative regulator of ABA signaling in seed germination and post-germination growth, which reveals that different members of the CDPK family may constitute a regulation loop by functioning positively and negatively in ABA signal transduction. We observed that both RNA interference and overexpression of CPK12 gene resulted in ABA-hypersensitive phenotypes in seed germination and post-germination growth, suggesting a high complexity of the CPK12-mediated ABA signaling pathway. CPK12 stimulates a negative ABA-signaling regulator (ABI2) and phosphorylates two positive ABA-signaling regulators (ABF1 and ABF4), which may partly explain the ABA hypersensitivity induced by both downregulation and upregulation of CPK12 expression. Our data indicate that CPK12 appears to function as a balancer in ABA signal transduction in Arabidopsis. 相似文献
10.
Naranjan S. Dhalla Vincenzo Panagia Naoki Makino Robert E. Beamish 《Molecular and cellular biochemistry》1988,82(1-2):75-79
In order to identify defects in Na+-Ca2+ exchange and Ca2+-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na+-dependent Ca2+ uptake, Na+-induced Ca2+ release, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na+-induced Ca2+-release. Similar results were obtained in Ca2+-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca2+ following a 5 min perfusion with Ca2+-free medium. Although a 2 min reperfusion of the Ca2+-free perfused hearts depressed sarcolemmal Ca2+-pump activities without any changes in Na+-induced Ca2+-release, Na+-dependent Ca2+ uptake was increased. These results indicate that alterations in the sarcolemmal Ca2+-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca2+ overload. 相似文献
11.
A high affinity Ca2+/Mg2+ ATPase has been identified and localized in synaptic membrane subfractions. This enzyme is stimulated by low concentrations of Ca2+ (1 M) believed to approximate the range of Ca2+ in the synaptosomal cytosol (0.1 to 5.0 M). The opiate agonist levorphanol, in a concentration-dependent fashion, inhibited Ca2+-stimulated ATP hydrolysis in lysed synaptic membranes. This inhibition was reversed by naloxone, while dextrorphan, the inactive opiate isomer, was without effect. Inhibition by levorphanol was most pronounced in a subfraction of synaptic membranes (SPM-1). The inhibition of Ca2+-stimulated ATP hydrolysis was characterized by a reduction inV
max for Ca2+. Levorphanol pretreatment reduced the Hill coefficient (HN) of 1.5 to 0.7, suggesting cooperative interaction between the opiate receptor and the enzyme protein. Levorphanol, but not dextrorphan, also inhibited (28%) ATP-dependent Ca2+ uptake by synaptic membranes. Opiate ligand stereoisomers were tested for their effects on calmodulin stimulating of high affinity Ca2+/Mg2+ ATPase in synaptic membranes. Levorphanol (10 M), but not the inactive stereoisomer (+)dextrorphan, significantly inhibited (35%) the calmodulin-activated Ca2+-dependent ATP hydrolysis activity in a preparation of lysed synaptic membranes. Both Ca2+-dependent and calmodulin-dependent stimulation of the enzyme in the presence of optimal concentrations of the other co-substrate were inhibited by levorphanol (35–40%) but not dextrorphan. Inhibition of ATP hydrolysis was characterized by a reduction inV
max for both Ca2+ and calmodulin stimulation of the enzyme. Calmodulin stimulation of enzyme activity was most pronounced in SPM-1, the membrane fraction which also exhibits the maximal opiate inhibition (40%) of the Ca2+-ATPase. The results demonstrate that opiate receptor activation inhibits a high affinity Ca2+/Mg2+ ATPase in synaptic plasma membranes in a stereospecific fashion. The inhibition of the enzyme may occur by a mechanism involving both Ca2+ and calmodulin. Inhibition of calmodulin activation may contribute to the mechanism by which opiate ligands disrupt synaptosomal Ca2+ buffering mechanisms. Changes in the cytosolic distribution of synaptosomal Ca2+ following inhibition of Ca2+/Mg2+ ATPase may underlie some of the pharmacological effects of opiate drugs. 相似文献
12.
Summary The two high affinity calcium binding sites of the cardiac (Ca2+ + Mg2+)-ATPase have been identified with the use of Eu3+. Eu3+ competes for the two high affinity calcium sites on the enzyme. With the use of laser-pulsed fluorescent spectroscopy, the environment of the two sites appear to be heterogeneous and contain different numbers of H2O molecules coordinated to the ion. The ion appears to be occluded even further in the presence of ATP. Using non-radiative energy transfer studies, we were able to estimate the distance between the two Ca2+ sites to be between 9.4 to 10.2 A in the presence of ATP. Finally, from the assumption that the calcium site must contain four carboxylic side chains to provide the 6–8 ligands needed to coordinate calcium, and based on our recently published data, we predict the peptidic backbone of the two sites. 相似文献
13.
With the help of a standard voltage-clamp technique, we investigated transmembrane ion currents in isolated smooth muscle
cells of the guinea pigtaenia coli. In Ca2+-dependent K+ current, we identified and studied the properties of an apamin-sensitive voltage-independent component carried through the
channels of low conductance (in many publications called small conductance,I
SK(Ca)). This component did not show the temporal inactivation;I
SK(Ca) was insensitive to the action of 4 mM tetraethylammonium, but was completely blocked by 500 nM of apamin. It was shown thatI
SK(Ca) is very sensitive to changes in the intracellular Ca2+ concentration ([Ca2+]
i
): a decrease in [Ca2+]
i
up to 50 nM resulted in the almost complete blockade of the current. The entry of Ca ions into a cell from the external solution
through the voltage-operated Ca2+ channels of L-type was not an obligatory condition for activation ofI
SK(Ca). The current-voltage relationship forI
SK(Ca) had a maximum within the voltage range of +20 to +50 mV.
Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 87–94, March–April, 2000. 相似文献
14.
PKC-induced sensitization of Ca2+-dependent exocytosis is mediated by reducing the Ca2+ cooperativity in pituitary gonadotropes
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The highly cooperative nature of Ca2+-dependent exocytosis is very important for the precise regulation of transmitter release. It is not known whether the number of binding sites on the Ca2+ sensor can be modulated or not. We have previously reported that protein kinase C (PKC) activation sensitizes the Ca2+ sensor for exocytosis in pituitary gonadotropes. To further unravel the underlying mechanism of how the Ca2+ sensor is modulated by protein phosphorylation, we have performed kinetic modeling of the exocytotic burst and investigated how the kinetic parameters of Ca2+-triggered fusion are affected by PKC activation. We propose that PKC sensitizes exocytosis by reducing the number of calcium binding sites on the Ca2+ sensor (from three to two) without significantly altering the Ca2+-binding kinetics. The reduction in the number of Ca2+-binding steps lowers the threshold for release and up-regulates release of fusion-competent vesicles distant from Ca2+ channels. 相似文献
15.
Massilia GR Eliseo T Grolleau F Lapied B Barbier J Bournaud R Molgó J Cicero DO Paci M Schininà ME Ascenzi P Polticelli F 《Biochemical and biophysical research communications》2003,303(1):238-246
Contryphan-Vn is a D-tryptophan-containing disulfide-constrained nonapeptide isolated from the venom of Conus ventricosus, the single Mediterranean cone snail species. The structure of the synthetic Contryphan-Vn has been determined by NMR spectroscopy. Unique among Contryphans, Contryphan-Vn displays the peculiar presence of a Lys-Trp dyad, reminiscent of that observed in several voltage-gated K(+) channel blockers. Electrophysiological experiments carried out on dorsal unpaired median neurons isolated from the cockroach (Periplaneta americana) nerve cord on rat fetal chromaffin cells indicate that Contryphan-Vn affects both voltage-gated and Ca(2+)-dependent K(+) channel activities, with composite and diversified effects in invertebrate and vertebrate systems. Voltage-gated and Ca(2+)-dependent K(+) channels represent the first functional target identified for a conopeptide of the Contryphan family. Furthermore, Contryphan-Vn is the first conopeptide known to modulate the activity of Ca(2+)-dependent K(+) channels. 相似文献
16.
Marianne S. Jurkowitz Gerald P. Brierley 《Journal of bioenergetics and biomembranes》1982,14(5-6):435-449
A rapid loss of accumulated Ca2+ is produced by addition of H+ to isolated heart mitochondria. The H+-dependent Ca+ efflux requires that either (a) the NAD(P)H pool of the mitochondrion be oxidized, or (b) the endogenous adenine nucleotides be depleted. The loss of Ca2+ is accompanied by swelling and loss of endogenous Mg2–. The rate of H+-dependent Ca2+ efflux depends on the amount of Ca2+ and Pi taken up and the extent of the pH drop imposed. In the absence of ruthenium red the H+-induced Ca2+-efflux is partially offset by a spontaneous re-accumulation of released Ca2+. The H+-induced Ca2+ efflux is inhibited when the Pi transporter is blocked withN-ethylmaleimide, is strongly opposed by oligomycin and exogenous adenine nucleotides (particularly ADP), and inhibited by nupercaine. The H+-dependent Ca2+ efflux is decreased markedly when Na+ replaces the K+ of the suspending medium or when the exogenous K+/H+ exchanger nigericin is present. These results suggest that the H+-dependent loss of accumulated Ca2+ results from relatively nonspecific changes in membrane permeability and is not a reflection of a Ca2+/H+ exchange reaction. 相似文献
17.
Netticadan T Temsah RM Kawabata K Dhalla NS 《Biochemical and biophysical research communications》2002,293(2):727-732
There is increasing evidence to suggest that Ca2+-calmodulin dependent protein kinase (CaMK) regulates the sarcoplasmic reticulum (SR) function and thus plays an important role in modulating the cardiac performance. Because intracellular Ca2+-overload is an important factor underlying cardiac dysfunction in a heart disease, its effect on SR CaMK was examined in the isolated rat heart preparations. Ca2+-depletion for 5 min followed by Ca2+-repletion for 30 min, which is known to produce intracellular Ca2+-overload, was observed to attenuate cardiac function as well as SR Ca2+-uptake and Ca2+-release activities. Attenuated SR function in the heart was associated with reduced CaMK phosphorylation of the SR Ca2+-cycling proteins such as Ca2+-release channel, Ca2+-pump ATPase, and phospholamban, decreased CaMK activity, and depressed levels of SR Ca2+-cycling proteins. These results indicate that alterations in cardiac performance and SR function following the occurrence of intracellular Ca2+-overload may partly be due to changes in the SR CaMK activity. 相似文献
18.
Vijayan Elimban Dayuan Zhao Naranjan S. Dhalla 《Molecular and cellular biochemistry》1987,77(2):143-152
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
19.
Summary Different cytochemical methods were employed to demonstrate the existence of Ca2+-binding sites (Ca2+-bs) at the membranes of barley root tip cells, involving addition of CaCl2 (10 mM or 1 mM) to all aqueous solutions used for tissue processing for electron microscopy, treatment of ultrathin sections by Ca-chelating agents, enzymic digestion of ultrathin sections and modification of Wachstein-Meisel procedure for localization of Ca2+-dependent ATPase activity. Addition of 10 mM CaCl2 to the fixatives and rinsing solutions causes electron-dense globules (EDG) to be formed in a variety of cells, those in cortical cells being associated mainly with the plasma membranes, in root cap cells with the plasmalemma as well as with majority of intracellular membranes. The obligatory presence of EDG at the membranes of Golgi vesicles and secretory vesicles approaching plasmalemma was revealed in the secreting root cap cells. Besides, electron opaque connecting material was found between the plasmalemma and adjacent secretory vesicle membranes. In true meristematic cells Ca-supplemented solutions induce formation of EDG localized at the ER membranes, and nuclear and plastid envelopes. In root cells of seeds germinated in the presence of 1 mM CaCl2 electron opaque deposits were found only in local areas of plasmalemma collars around plasmodesmata neck regions, contacting the terminals of subsurface ER channels. In control speciemens (germination, fixation and washing without added CaCl2) EDG were absent in cortical and ground meristem cells, but present in root cap cells, although their number and average size were greatly reduced.Treatment of thin sections by 10mM EGTA or EDTA led to complete removing of EDGs, electron-transparent holes replacing them. Digestion by a variety of proteolytic enzymes and by phospholipase A induced partial destruction of EDG matrices, confirming the presence of protein as well as of phospholipid membrane components. Visualization of electron-dense granular product of cytochemical Ca-ATPase reaction at the same membrane areas where EDG were located suggests that one of the Ca-binding proteins in EDG may represent Ca-ATPase.It is proposed that EDG at plant cell membranes have a certain resemblance to the Ca2+-bs revealed by the same method on plasma membrane of a variety of animal cells. The data obtained are discussed regarding possible regulatory roles of calcium ions in plant cells, especially in exocytotic secretion. 相似文献
20.
Although cis-diamminedichloroplatinum (II) (cisplatin) is a potent anticancer drug, clinical use of this agent is highly limited predominantly because of its strong side effects on the kidney and gastrointestinal tracts. We found that cisplatin impaired respiratory function and DNA of mitochondria in renal proximal tubules and small intestinal mucosal cells, thereby inducing apoptosis of epithelial cells. Cisplatin-induced mitochondrial dysfunction and DNA (mtDNA) injury, lipid peroxidation, and apoptosis of epithelial cells in the kidney and small intestine were strongly inhibited by L-carnitine. However, carnitine had no appreciable effect on the tumoricidal action of cisplatin against cancer cells inoculated in the peritoneal cavity. These results indicate that L-carnitine may have therapeutic potential for inhibiting the side effects of cisplatin and other anticancer agents in the kidney and small intestine. 相似文献