共查询到20条相似文献,搜索用时 62 毫秒
1.
Paired sedimentation studies of isolated, native thick filaments at pH 6.8, I = 0.12 and in the presence of 0.3 mm-free Mg2+ show that the sedimentation coefficient increases with Ca2+ concentration (pCa2 midpoint = 5.5), leveling off at pCa 4.7. The addition of ATP or ADP (5 mm) has no effect on the hydrodynamic changes induced by Ca2+. At much higher free Mg2+ concentrations (5 mm), the midpoint of the transition is shifted to pCa = 5.3. Viscosity measurements of the filament system under comparable conditions reveal a decrease in the relative viscosity over the same range of Ca2+ concentration. Synthetic filaments prepared from purified myosin free of C-protein also show the same behavior. Native filaments from which myosin heads have been removed by treatment with papain do not show Ca2+ dependence. The dependence of the sedimentation coefficient of filament on protein concentration, as measured by differential sedimentation, is unaffected by Ca2+, indicating that the changes in hydrodynamic properties are probably not related to aggregation of the filaments. The Ca2+ effects are reversible and are not observed on replacing Ca2+ by Mg2+. Binding studies carried out at low ionic strength reveal two binding sites for Ca2+ (Ka = 1.7 × 105m?1) per mole myosin within the filament and evidence is presented showing that the DTNB light chain is the site of binding. The combined results are interpreted as indicating that thick filaments of vertebrate muscle undergo conformational changes at physiological levels of Ca2+ and provide evidence for a Ca2+-sensitive regulatory mechanism at the level of the thick filament. 相似文献
2.
MARK MCMENAMIN 《Invertebrate reproduction & development.》2013,57(2-3):165-166
Summary The role of Ca2+ in activation and early development of locust eggs was examined through measurement of ooplasmic Ca2+ levels before and after fertilization, and through experimental activation of unfertilized eggs. Ooplasmic pCa (i.e. the negative logarithm of Ca2+ activity) measured in intact eggs decreased from 5.35 before fertilization, to 4.77 and 3.00 by 1 day and 3 days after fertilization, respectively. pCa was also determined for samples of ooplasm collected by rupturing eggs under paraffin oil. The pCa was 5.10 in ooplasm isolated from unfertilized eggs, and 3.84 in ooplasm collected from eggs within 4 h of fertilization. Ooplasmic pCa remained between 3.97 and 3.12 from 1–6 days after fertilization. Since a decline in pCa indicates an increase in ooplasmic Ca2+ activity, the data suggest that regulation of ooplasmic Ca2+ during post-fertilization development involves release of Ca2+ from internal stores. Experimental egg activation was examined in eggs dissected from the oviducts before fertilization and incubated on moist filter paper. Some eggs were first immersed in experimental solutions for 30–60 minutes before incubation. The presence of an embryo 2 or 4 days after fertilization or experimental treatment was used as an indicator of egg activation. Activation occurred in 92% and 12% of fertilized and untreated eggs, respectively. The percentage of unfertilized eggs which activated increased to 47% if eggs were soaked 30–60 minutes in physiological saline, and to as much as 65%-68% if eggs were injected with Ca2+ buffers or if a Ca2+ action potential was evoked. Up to 36% and 42% of unfertilized eggs activated after incubation in Ca2+-free salines or in the presence of the Ca2+-channel blocker Cd2+, respectively. Taken together, the results suggest that entry of external Ca2+ through voltage dependent channels increases the proportion of eggs which activate, but is not an absolute requirement for activation. 相似文献
3.
The rate constant of modification of a specific thiol group, SH2, with N-ethylmaleimide (NEM) has been used to estimate the conformational change in the local area containing SH2 (SH2 region) of skeletal myosin as a structural probe. The rate of Mg2+-ATP-induced SH2 modification of subfragment-1 (S-l) isozymes was regulated by Ca2+ in the pCa range below 6.4 and was not regulated in the pCa range above 6.4. No substantial difference between S-1 containing alkali light chain, A1, (S-1(A1)) and S-1 containing alkali light chain, A2, (S-1(A2)) was observed in the Ca2+-dependent rate of SH2 modification. Due to the presence of this Ca2+ regulation in myosin (absence in S-1 isozymes) in the pCa range above 6.4, absence of 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) light chain in S-1 isozymes, and high affinity of Ca2+ for DTNB light chain, this Ca2+ regulation in the pCa range above 6.4 is possibly related to the Ca2+ binding to DTNB light chain. F-Actin, which is entirely free from tropomyosin and troponin, enhanced the rate of Mg2+-ATP-induced SH2 modification of S-1 isozymes equally and of myosin, and reduced the Ca2+ sensitivity with an increase in F-actin concentration. 相似文献
4.
Shilpa Rani Chang Sik Park Pradeep Kumar Sreenivasaiah Do Han Kim 《Molecules and cells》2016,39(2):149-155
In the heart, excitation-contraction (E-C) coupling is mediated by Ca2+ release from sarcoplasmic reticulum (SR) through the interactions of proteins forming the Ca2+ release unit (CRU). Among them, calsequestrin (CSQ) and histidine-rich Ca2+ binding protein (HRC) are known to bind the charged luminal region of triadin (TRN) and thus directly or indirectly regulate ryanodine receptor 2 (RyR2) activity. However, the mechanisms of CSQ and HRC mediated regulation of RyR2 activity through TRN have remained unclear. We first examined the minimal KEKE motif of TRN involved in the interactions with CSQ2, HRC and RyR2 using TRN deletion mutants and in vitro binding assays. The results showed that CSQ2, HRC and RyR2 share the same KEKE motif region on the distal part of TRN (aa 202–231). Second, in vitro binding assays were conducted to examine the Ca2+ dependence of protein-protein interactions (PPI). The results showed that TRN-HRC interaction had a bell-shaped Ca2+ dependence, which peaked at pCa4, whereas TRN-CSQ2 or TRN-RyR2 interaction did not show such Ca2+ dependence pattern. Third, competitive binding was conducted to examine whether CSQ2, HRC, or RyR2 affects the TRN-HRC or TRN-CSQ2 binding at pCa4. Among them, only CSQ2 or RyR2 competitively inhibited TRN-HRC binding, suggesting that HRC can confer functional refractoriness to CRU, which could be beneficial for reloading of Ca2+ into SR at intermediate Ca2+ concentrations. 相似文献
5.
Powers Frances M. Palmiter Kimberly A. Solaro R. John 《Molecular and cellular biochemistry》1996,160(1):33-39
E-1020 is a cardiotonic agent that acts as a cyclic-AMP phosphodiesterase inhibitor but also may have actions which alter myofilament response to Ca2+. To identify direct actions of E-1020 on cardiac contractile proteins, effects of E-1020 on myofibrillar Ca2+ dependent MgATPase and force generation in chemically skinned fiber bundles were measured. In bovine cardiac myofibrils, E-1020 (100 M) significantly increased myofilament Ca2+ sensitivity and Ca2+-dependent ATPase activity at submaximal pCa values. At pCa 6.75, E-1020 significantly increased ATPase activity in bovine (10–100 pM) and canine (1–100 pM) cardiac myofibrils but had no effect on rat cardiac myofibrils. Moreover, in one population of canine ventricular fiber bundles, E-1020 (0.0–10 M) significantly increased isometric tension at pCa 6.5 and 6.0, whereas in another population of bundles E-1020 had no effect on tension. In no case was resting (pCa 8.0) or maximal tension (pCa 4.5) increased by E-1020. Measurements of Ca2+ binding to canine ventricular skinned fiber preparations demonstrated that E-1020 does not alter the affinity of myofilament troponin C for Ca2+. We conclude that part of the mechanism by which E-1020 acts as an inotropic agent may involve alterations in the responsiveness of contractile proteins to Ca2+. The lack of effect of E-1020 on some preparations may be dependent on isoform populations of myofilament proteins. 相似文献
6.
Tudor Porumb A. Crivici Perry J. Blackshear M. Ikura 《European biophysics journal : EBJ》1997,25(4):239-247
The myristoylated alanine-rich C kinase substrate (MARCKS) and the MARCKS-related protein (MRP) are members of a distinct
family of protein ki-nase C (PKC) substrates that bind calmodulin (CaM) in a manner regulated by Ca2+ and phosphorylation by PKC. The CaM binding region overlaps with the PKC phosphorylation sites, suggesting a potential coupling
between Ca2+-CaM signalling and PKC-mediated phosphorylation cascades. We have studied Ca2+ binding of CaM complexed with CaM binding peptides from MARCKS and MRP using flow dialysis, NMR and circular dichroism (CD)
spectroscopy. The wild-type MARCKS and MRP peptides induced significant increases in the Ca2+ affinity of CaM (pCa 6.1 and 5.8, respectively, compared to 5.2, for CaM in the absence of bound peptides), whereas a modified
MARCKS peptide, in which the four serine residues susceptible to phosphorylation in the wild-type sequence have been replaced
with aspartate residues to mimic phosphorylation, had smaller effect (pCa 5.6). These results are consistent with the notions
that phosphorylation of MARCKS reduces its binding affinity for CaM and that the CaM binding affinity of the peptides is coupled
to the Ca2+ affinity of CaM. All three MARCKS/MRP peptides perturbed the backbone NMR resonances of residues in both the N- and C-terminal
domains of CaM and, in addition, the wild-type MARCKS and the MRP peptides induced strong positive cooperativity in Ca2+ binding by CaM, suggesting that the peptides interact with the amino- and carboxy-terminal domains of CaM simultaneously.
NMR analysis of the Ca2+-CaM-MRP peptide complex, as well as CD measurements of Ca2+-CaM in the presence and absence of MARCKS/MRP peptides suggest that the peptide bound to CaM is non-helical, in contrast
to the α-helical conformation found in the CaM binding regions of myosin light-chain kinase and CaM-dependent protein kinase II. The
adaptation of the CaM molecule for binding the peptide requires disruption of its central helical linker between residues
Lys-75 and Glu-82.
Received: 26 September 1996 / 22 October 1996 相似文献
7.
The activation of rabbit muscle, liver, and kidney fructose bisphosphatases by histidine and citrate 总被引:2,自引:0,他引:2
A G Datta B Abrams T Sasaki J W van den Berg S Pontremoli B L Horecker 《Archives of biochemistry and biophysics》1974,165(2):641-645
Purified fructose 1,6-bisphosphatases from rabbit muscle, liver, and kidney require a metal chelator for optimal activity at neutral pH. This requirement is satisfied by physiological concentrations of histidine and citrate, and at pH 7 their effects are additive. In the presence of both histidine and citrate the optimum activity is shifted from about pH 8 to pH 7.2, and the activity is greater than that obtained with optimal concentrations of EDTA. Carnosine, anserine, and 1-methyl histidine are also effective, but only at much higher concentrations, while 3-methyl histidine is effective in the same concentration range as is histidine. Isocitrate can replace citrate. The results suggest that fructose bisphosphatases possess distinct binding sites for divalent cations (Mg2+ or Mn2+) and also for histidine and citrate complexes of these cations. 相似文献
8.
Allan C. Stam Jr. William B. Weglicki Edward W. Gertz Edmund H. Sonnenblick 《生物化学与生物物理学报:生物膜》1973,298(4):927-931
An active intracellular to extracellular Ca2+ efflux has been proposed in heart muscle. A myocardial sarcolemmal ATPase stimulated by an intracellular pCa and serving as a Ca2+ pump has been postulated. A recently developed myocardial sarcolemmal preparation has not permitter a search for such an enzymatic activity. In these studies, an ATPase has been demonstrated in the sarcolemma which is activated by Mg2+, stimulated as the Ca2+ is raised to a pCa of 6, and is inhibited by ouabain. These findings suggest a mechanism by which Ca2+ within the myocardium may be modulated and thus how the force of contraction may be altered by cardiac glycosides. 相似文献
9.
Insect indirect flight muscle is activated by sinusoidal length change, which enables the muscle to work at high frequencies, and contracts isometrically in response to Ca2+. Indirect flight muscle has two TnC isoforms: F1 binding a single Ca2+ in the C-domain, and F2 binding Ca2+ in the N- and C-domains. Fibres substituted with F1 produce delayed force in response to a single rapid stretch, and those with F2 produce isometric force in response to Ca2+. We have studied the effect of TnC isoforms on oscillatory work. In native Lethocerus indicus fibres, oscillatory work was superimposed on a level of isometric force that depended on Ca2+ concentration. Maximum work was produced at pCa 6.1; at higher concentrations, work decreased as isometric force increased. In fibres substituted with F1 alone, work continued to rise as Ca2+ was increased up to pCa 4.7. Fibres substituted with various F1:F2 ratios produced maximal work at a ratio of 100:1 or 50:1; a higher proportion of F2 increased isometric force at the expense of oscillatory work. The F1:F2 ratio was 9.8:1 in native fibres, as measured by immunofluorescence, using isoform-specific antibodies. The small amount of F2 needed to restore work to levels obtained for the native fibre is likely to be due to the relative affinity of F1 and F2 for TnH, the Lethocerus homologue of TnI. Affinity of TnC isoforms for a TnI fragment of TnH was measured by isothermal titration calorimetry. The Kd was 1.01 μM for F1 binding and 22.7 nM for F2. The higher affinity of F2 can be attributed to two TnH binding sites on F2 and a single site on F1. Stretch may be sensed by an extended C-terminal domain of TnH, resulting in reversible dissociation of the inhibitory sequence from actin during the oscillatory cycle. 相似文献
10.
Survival and death of Chara internodal cells in electrolyte solutions and calcium release from the cell wall 总被引:4,自引:4,他引:0
Abstract. Survival and death of Chara internodal cells were investigated in one of the alkali metal salts KCl, some of the alkali earth metal salts CaCl2, Ca(NO3)2, MgCl2, Mg(NO3)2, SrCl2, Sr(NO3)2, BaCl2 and Ba(NO3)2, potassium phosphate pH buffer solution (pH 7.0), Tris-maleate pH buffer solution (pH 7.0), HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid)-KOH (pH 7.0) pH buffer solution, calcium buffer solutions, and deionized water. Most of the internodal cells died within a day or a few days in KCl, MgCl2, Mg(NO3)2, BaCl2 and Ba(NO3)2 solutions of higher concentrations, calcium buffer solutions of pCa 6.0, 10.0 mol m-3 potassium phosphate pH buffer solution and 10.0 mol m-3 Trismaleate pH buffer solution. However, all of the internodal cells survived more than 10 d in deionized water, 80.0 mol m-3 CaCl2, 80.0 mol m-3 Ca(NO3)2, 80.0 mol m-3 SrCl2, 80.0 mol m-3 Sr(NO3)2 calcium buffer solutions of pCa 4.0 and pCa 5.0, and 10.0 mol m-3 HEPES-KOH (pH 7.0) pH buffer solution. Addition of Ca2+ or Sr2+ to K+, Mg2+ and Ba2+ salt solutions increased the survival rates of the internodal cells. Calcium release from the internodal cell wall was measured in deionized water, KCl, NaCl, MgCl2, CaCl2, SrCl2 and BaCl2 solutions. Except in deionized water and CaCl2 solution, most of the calcium binding to the cell wall was released within one or a few hours in respective electrolyte solutions. Thus, survival and death of the internodal cells in the electrolyte solutions tested were interpreted in terms of the calcium release from the cell wall and the cell membrane, and intrinsic ability of Sr2+ to maintain the cell membrane normal. 相似文献
11.
Donald J. Messner Christine Surrago Celia Fiordalisi Wing Yin Chung Kris V. Kowdley 《Biometals》2017,30(5):699-708
Iron overload disorders may be treated by chelation therapy. This study describes a novel method for isolating iron chelators from complex mixtures including plant extracts. We demonstrate the one-step isolation of curcuminoids from turmeric, the medicinal food spice derived from Curcuma longa. The method uses iron-nitrilotriacetic acid (NTA)-agarose, to which curcumin binds rapidly, specifically, and reversibly. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin each bound iron-NTA-agarose with comparable affinities and a stoichiometry near 1. Analyses of binding efficiencies and purity demonstrated that curcuminoids comprise the primary iron binding compounds recovered from a crude turmeric extract. Competition of curcuminoid binding to the iron resin was used to characterize the metal binding site on curcumin and to detect iron binding by added chelators. Curcumin-Iron-NTA-agarose binding was inhibited by other metals with relative potency: (>90% inhibition) Cu2+ ~ Al3+ > Zn2+ ≥ Ca2+ ~ Mg2+ ~ Mn2+ (<20% inhibition). Binding was also inhibited by pharmaceutical iron chelators (desferoxamine or EDTA) or by higher concentrations of weak iron chelators (citrate or silibinin). Investigation of the physiological effects of iron binding by curcumin revealed that curcumin uptake by cultured cells was reduced >80% by addition of iron to the media; uptake was completely restored by desferoxamine. Ranking of metals by relative potencies for blocking curcumin uptake agreed with their relative potencies in blocking curcumin binding to iron-NTA-agarose. We conclude that curcumin can selectively bind toxic metals including iron in a physiological setting, and propose inhibition of curcumin binding to iron-NTA-agarose for iron chelator screening. 相似文献
12.
Carlos A. Perez 《Journal of inorganic biochemistry》2009,103(3):326-332
Baicalein and baicalin, the major bioactive compounds found in the Chinese herb Scutellaria baicalensis, have been shown to be effective against cancer, bacterial infections and oxidative stress diseases. However, little is known about their mechanisms of action. To probe whether iron homeostasis modulation may play a role in their bioactivity, we have investigated their iron binding characteristics under physiologically relevant conditions. A 2:1 baicalein-ferrous complex was readily formed in 20 mM phosphate buffer, pH 7.2, with a binding constant ∼2-9 × 1011 M−2, whereas a 1:1 baicalein-ferric complex was formed, under the same conditions, with an apparent binding constant ∼1-3 × 106 M−1. Baicalein appears to bind the ferrous ion more strongly than ferrozine, a well known iron(II) chelator. Using 1 H NMR and Zn2+ and Ga3+ as probes, the iron-binding site on baicalein was elucidated to be at the O6/O7 oxygen atoms of the A-ring. No binding was observed for baicalin under the same NMR conditions. Furthermore, baicalein strongly inhibits the Fe-promoted Fenton chemistry via a combination of chelation and radical scavenging mechanism while baicalin can provide only partial protection against radical damage. These results indicate that baicalein is a strong iron chelator under physiological conditions and hence may play a vital role in modulating the body’s iron homeostasis. Modulation of metal homeostasis and the inhibition of Fenton chemistry may be one of the possible mechanisms for herbal medicine. 相似文献
13.
The binding of Ca2+ and Mg2+ ions to commercially available and easily synthesizable metallochromic indicators has been systematically examined at pH 7.35, temperature 37°C, ionic strength 0.16, the conditions of blood plasma. The pCa and pMg midpoints of the colour changes of all the useful indicators are reported. In addition to the well-known indicators arsenazo III, chlorophosphonazo III, antipyrylazo III, and murexide for Ca2+, and Eriochrome Black T and Eriochrome Blue SE for Mg2+, we draw attention to the values of oxyacetazo I, carboxyazo III, tropolone, methylthymol blue, Mordant Black 32, and the tetracyclines. 相似文献
14.
H. Satoh 《Amino acids》1995,9(3):235-246
Summary Effects of taurine on the delayed rectifier K+ channel in isolated 10-day-old embryonic chick ventricular cardiomyocytes were examined at different intracellular Ca2+ concentrations ([Ca]i), using whole-cell voltage and current clamp techniques. Experiments were performed at room temperature (22°C). Test pulses were applied between -20 to +90m V from a holding potential of -40mV. When [Ca]i was pCa 7, addition of 10 and 20 mM taurine to the bath solution reduced the delayed rectifier K+ current (IK) at +90mV by 17.4 ± 2.8% (n = 5, P < 0.01) and 25.5 ± 2.6% (n = 5, P < 0.001), respectively. In contrast, when [Ca]i was pCa 10, IK at +90 mV was enhanced by 19.1 ± 3.1% (n = 7, P < 0.01) at 10mM taurine, and by 29.3 ± 2.4% (n = 7, P < 0.001) at 20mM taurine. The voltage of half-maximum activation (V1/2) was shifted in a hyperpolarizing direction; at pCa 7, the value was +0.2 ± 2.2mV (n = 5) in control and -10.6 ± 1.8mV (n = 5) in 20mM taurine. At pCa 10, the V1/2 value was +18.5 ± 4.6mV (n = 5) in control and +6.6 ± 5.2mV (n = 5) in taurine (20mM). Taurine decreased the action potential duration (APD) at pCa 10, but at pCa 7 did not affect it. In addition, taurine enhanced the transient outward current in a concentration-dependent manner. These results indicate that taurine modulates the delayed rectifier K+ channel, an effect dependent on [Ca]i and capable of regulating APD. 相似文献
15.
Using non-invasive ion-selective microprobes, that were placed in substomatal cavities, long-distance signalling has been
investigated in intact Hordeum vulgare and Vicia faba seedlings. Heat (flame), applied to one leaf (S-leaf), triggers apoplastic ion activity (pH, pCa, pCl) transients in a distant
leaf (T-leaf), all largely independent of simultaneously occurring action potential-like voltage changes. While apoplastic
pCa and pH increase (Ca2+-, H+-activities decrease), pCl decreases (Cl−-activity increases). As the signal transfer from the S- to the T-leaf is too fast to account for mass flow, the heat-induced
pressure change is primarily responsible for changes in voltage (H+ pump deactivation) as well as for the ion fluxes. The pCa transient precedes the pCl- and pH responses, but not the voltage
change. Since the apoplastic pCl decrease (Cl− increase) occurs after the pCa increase (Ca2+ decrease) and after the depolarization, we argue that the Cl− efflux is a consequence of the Ca2+ response, but has no part in the depolarization. Kinetic analysis reveals that pH- and pCl changes are interrelated, indicated
by the action of the anion channel antagonist NPPB, which inhibits both pCl- and pH changes. It is suggested that efflux of
organic anions into the apoplast causes the pH increase rather than the deactivation of the plasma membrane H+ pump. Since there is considerably more information in ion activity changes than in a single action- or variation potential
and heat-induced ion fluxes occur more reliably than voltage changes, released by milder stimuli, they are considered systemic
signalling components superior to voltage. 相似文献
16.
Both ADP production and tension have been measured in segments of chemically skinned fibers contracting at different Ca2+ concentrations. Full mechanical activation occurred between pCa 7.00 and pCa 6.50. The total ATPase was due to both actomyosin and non-actomyosin ATPase. Actomyosin ATPase was observed at pCa 7.09 without accompanying tension. The Ca2+ dependence of tension was steeper than actomyosin ATPase. This finding implies some rate constants of the mechanochemical cycle are Ca2+ dependent. Non-actomyosin ATPase was measured in fibers stretched beyond overlap of the thick and thin filaments. Sarcoplasmic reticulum was isolated and sarcoplasmic reticulum activity was measured in vitro under the same conditions as the single-fiber experiments. Non-actomyosin ATPase in the single fibers was found to be small compared to maximally activated actomyosin ATPase but larger than the ATPase that could be attributed to sarcoplasmic reticulum activity. 相似文献
17.
Adawia A. Alousi Alison M. Grant John R. Etzler Barry R. Cofer Joanna Van der Bel-Kahn David Melvin 《Molecular and cellular biochemistry》1990,96(1):79-88
In this study we tested the hypothesis that reduced myofibrillar ATPase activities in end-stage heart failure are associated with a redistribution of myosin isozymes. Cardiac myofibrils were isolated from left ventricular free wall from normal human hearts and hearts at end-stage heart failure caused by coronary artery diseases, cardiomyopathy or immunological rejection. The hearts had been excised in preparation for a heart transplant. Myofibrillar Ca2–-dependent Mg-ATPase and myosin Ca–- and K–EDTA-ATPase activities were compared. Possible changes in myosin isozyme distribution in the diseased heart were investigated using polyacrylamide gel electrophoresis of native myosin in the presence of pyrophosphate. Significant reduction in myofibrillar Ca2+-dependent Mg-ATPase with no changes in the sensitivity of the myofibrils to Ca+ was observed in heart with coronary artery diseases (25.2 to 27.1% at pCa 5.83 to pCa 5.05), cardiomyopathy (21.1 to 25.5% at pCa 5.41 to pCa 5.05), and in the immunologically rejected heart (18.4 to 22.8% at pCa 5.41 to pCa 5.05). Significantly lower myosin Ca2+-ATPase was observed with coronary artery diseases only and myosin K-EDTA activities did not differ in diseased and normal hearts. Polyacrylamide gel electrophoresis of native myosin from the normal and three models of end-stage heart failure revealed two distinct bands in the human left ventricle and one diffuse band in the human right atria. No apparent differences in myosin isoenzyme pattern were observed between the normal and diseased hearts. Further evaluation is needed to clarify the ATPase nature of the two bands. 相似文献
18.
Contraction in vertebrate striated muscle is known to be dependent upon the binding of calcium ions to the regulatory protein troponin C (TnC). Our electrical (Donnan potential) studies of the subsarcomeric regions have revealed an electrical switching mechanism, which is sensitive to both cation concentration and to particular anions. In a buffer containing phosphate and chloride ions and at 2.7 mM Mg2+ we observe a single charge transition at pCa50 6.8 in both A- and I-bands. At zero Mg2+ the pCa50 of the A-band transition is shifted to 8.0 and the I-band shows two transitions (pCa50 approximately 6.8 and approximately 8.2). Increasing [Mg2+] to 4.5 mM produces a complex effect between pCas 7 and 9 in both bands. All effects are abolished at 9 mM Mg2+. In a chloride-only buffer (imidazole) at zero Mg2+ the direction of the charge transitions is reversed. In addition, two transitions (pCa50 approximately 8.5 and approximately 7.0) are evident in the A-band and three in the I-band (pCa50 approximately 8.5, approximately 7.4, approximately 6.7). In the presence of Mg2+, again the effects of pCa upon the Donnan potential are complex. In the A-band at 2.7 mM Mg2+ two transitions of opposite sign predominate (pCa approximately 7 and approximately 8), whilst in the I band a single transition (pCa approximately 8.3) occurs in the same direction as that observed in phosphate buffer. At 4.5 mM Mg2+ the 'W' shape observed in the corresponding phosphate buffer is preserved in both bands with similar pCa50s. This shape is also apparent in the 9 mM Mg2+ solution. In these two buffer systems, the magnitude of the charge change in terms of electron binding is far larger than expected from simple Ca2+/Mg2+ binding to troponin. In an acetate-only buffer, however, the Donnan potentials of the A-band and I-band were very similar in magnitude and the charge change across the full pCa curve is close to the expected value for Ca2+/Mg2+ binding to troponin. We speculate that titin has a role in the calcium activation of striated muscle in vertebrates for four reasons. First, the effects of long-term storage of the glycerinated muscle; second, the action of [Mg2+]ions; third the effect of anions; and fourth, our published and unpublished observations of sarcomere-length dependence. We also demonstrate the validity of our methodology, relating the charge transitions that we observe to cation-binding studies of a more traditional nature. 相似文献
19.
Shimamoto Y Suzuki M Ishiwata S 《Biochemical and biophysical research communications》2008,366(1):233-238
The length-dependent activation of skeletal myofibrils was examined at the single-sarcomere level with phase-contrast microscopy at sarcomere length (SL) >2.2 μm. At the maximal activation by Ca2+ (pCa 4.5) the active force linearly decreased with increasing SL, while at partial activation by Ca2+ (pCa 6.1-6.5) the larger active force was generated at longer SL. Throughout these experiments, the distribution of SL was kept homogeneous upon activation. In addition, we found that the spontaneous oscillation of force and SL frequently occurs in the SL range 2.2-2.6 μm at pCa 6.1-6.2. Either changes in [Ca2+] or osmotic compression of the myofilament lattice induced by the addition of dextran T-500, affected both the length dependence of activation and the occurrence of auto-oscillation. These results suggest that the force-generating properties of sarcomeres in striated muscle are determined not only by [Ca2+], but also by the lattice spacing as a function of SL. 相似文献
20.
Dorota Rutkowska-Zbik Małgorzata Witko Leszek Fiedor 《Journal of molecular modeling》2013,19(11):4661-4667
Water binding to several Mg2+ chelates, ethylenediamine, ethylenediamine-N,N’-diacetate, porphyrin, chlorophyll a and bacteriochlorophyll a, to form five- and six-coordinate complexes is studied by means of density functional theory. The results obtained for magnesium chelates are compared with the properties of the respective aqua complexes and the influence of the permittivity of environment on the ligand binding energies is discussed. Although the most common coordination number of Mg2+ is six, in the tetrapyrrolic chelates it is reduced to five because the accommodation of the sixth water ligand results in no gain in energy. This is in line with the experimental observations made for coordination of chlorophylls in vivo. The binding between Mg2+ and water is mostly of electrostatic nature, which is supported by the finding that its energy is correlated both with the electron density of the chelator and with electrostatic potential determined at the ligand binding site. 相似文献