首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 216 毫秒
1.
研究了超越亚纯函数的分式线性变换的特征函数与其导数的特征函数增长性的比较,并由Nevanlinna理论推导出一个定理,其主要结果为:T(r,F)<40λλ-1logeλλ-1T(λr,f′)+log+(λr)+log+|f(0)|+5+log+ad+log+bd+log2(c=0)T(r,F)<40λλ-1logeλλ-1T(λr,F′)+log+(λr)+log+|F(0)|+5+log+ad-bcc2+log+dc+log2+h(r)(c≠0)  相似文献   

2.
秩为r的不可约单项式的集合Sr可以直接转化为S(r+1),多项式守恒密度T(r+1)=T_(r+1) ̄0+U_(r+1),T_(r+1) ̄0的每一项都含因子u_0,可从T_r得到U_(r+1)(CS_(r+1))的每一项不含因子u_0,U_(r+1)与T_(r+1) ̄0的项之间存在着特殊的相关性,由此可分批求出U_(r+1)中的特定系数且不涉及X_(r+1)。  相似文献   

3.
如果(n+1) ̄2+(n+2) ̄2+…+(n+k) ̄2=(n+k+1) ̄2+(n+k+2) ̄2+…+(n+2k-m) ̄2,则称n+1,n+2,…,n十k,n+k+1,…,n+2k-m为一组m类连续勾股数.给出了寻找m类连续勾股数的一种方法.并由此得到了下列结果:1.m=1时,连续勾股数只有已知的唯一形式(n=1,2,3,…):(2n ̄2+n) ̄2+(2n ̄2+n+1) ̄2+…+(2n ̄2+2n) ̄2=(2n ̄2+2n+1) ̄2+…+(2n ̄2+3n) ̄22.下列的m类连续勾股数不存在:m≡3(mod8),m≡4(mod8),m≡5(mod8).3.当2≤m≤100时,只有6组m类连续勾股数.还给出了一个连续勾股数的构造定理,由此可导出一系列k=tm型的连续勾股数.  相似文献   

4.
证明了在经典Adams谱序列中,当P≥11,3≤s≤P-3时,g0(b1)^2∈ExtA^6,2p^2q+pq+2q(H*V(2),Zp)在,Adams谱序列中收剑到π2p^2q+pq+2q-V(2)的非零元,g0(b1)^2γ,∈ExtA^6+s,(s+2)p^2q+spq+sq+(s-3)(Zp,Zp)在Adams谱序列中收剑到π(s+2)p^2q+spq+sq-9S的非零元。  相似文献   

5.
引入一种新的正线性算子并研究它对于无界函数的同时逼近.设f∈Cβ[0,∞),r∈N,f(x)在[0,∞)存在r阶导数,则limn∞M(r)n,α(f(t),x)=f(r)(x);若f(r)(x)∈C(a-η,b+η)(η>0),则M(r)n,α(f,x)f(r)(x)在x∈[a,b]一致成立.设f∈Cβ[0,∞),f(x)在[0,∞)上存在r+2阶导数,则limn∞n[M(r)n,α(f,x)-f(r)(x)]=α[r(r+1)f(r)(x)+(2(r+1)x+r)f(r+1)(x)+x(1+x)f(r+2)(x)];若f(r+2)(x)∈Ca-η,b+η)(η>0),则上式在[a,b]一致成立.  相似文献   

6.
盐毒害作用包括渗透胁迫和离子胁迫两大类,它们都能严重影响根系和新稍的生长。Na~+减少了质膜对Ca~(++)的束缚,当Ca~(++)向外流出增加时,Na~+能抑制Ca~(++)进入胞内,并耗尽内质膜上的Ca~(++),这些变化表明,Ca~(++)的变化是根系细胞受到盐胁迫后的原初反应。盐能很快减少Ca~(++)向叶细胞的转运,Na~+干扰了根系细胞内Ca~(++)的平衡,盐胁迫时补Ca~(++)能产生良好作用。  相似文献   

7.
合成了分别含Li ̄+,Na ̄+,K ̄+和Mg ̄(2+),Ca ̄(2+),Ba ̄(2+)的6种乙丙三元胶(EPDM)磺酸盐离聚体,溶解性试验反映出固体中存在聚集引起的离子交联,红外光谱表明金属离子与的相互作用为Li ̄+>Na ̄+>K ̄+和Mg ̄(2+)>Ca ̄(2+)>Ba ̄(2+)及M ̄(2+)>M ̄+,通过动态力学分析,讨论了离聚体中离子相互作用对离子聚集和橡胶平台区温度范围的影响规律。  相似文献   

8.
研究一类一阶非线性时滞微分方程,x′(t)+a(r)f(x(t))+p(t)g(x(t))h(x(t-τ1(t)),x(t-τ2(t)),…,x(t-τn(t)))=0,其中,a,p,τj∈C(R^+,R^+),limt→+∞(t-τ1(t))=+∞,j=1,2,…,n,f,g∈C(R,R),获得了其存在正解的充分条件。  相似文献   

9.
本文研究了一阶非线性具偏差变元的超前型泛函微分方程:x(t)=a(t)∏mi=1[x(t+rj(t))]αj(*)及x(t)=a(t)f[x(t+r1(t)),x(t+r2(t)),…,x(t+rm(t)]+g[t,x(t),x(t+r1(t)),…,x(t+rm(t))](**)解的振动性问题,给出了方程(*)与(**)解振动的充分条件  相似文献   

10.
研究了(Y,Ce,Sm)(Mg,Mn)B5O(10)中Sm(3+)和Mn(2+)的发光性质,Mn(2+)浓度对Sm(3+)发射的影响.着重讨论了Mn(2+)对Sm(3+)发射的敏化作用及能量传递机理.  相似文献   

11.
蚯蚓钙调素结合蛋白的研究   总被引:9,自引:0,他引:9  
以赤子爱胜蚓(Eisenia Foetida)为材料,通过DEAE-Fast Flow离子交换层析、CaM-Sepharose亲和层析,分离纯化得到蚯蚓钙调素结合蛋白(CaMBPs)。纯化的CaMBPs对CaM激活的环核苷酸磷酸二酯酶活性有抑制作用,而且这种抑制作用可通过加入过量的CaM达到完全恢复。SDS-PAGE显示CaMBPs有3条明显主带,在EGTA存在时表现分子量分别为62, 49和30kD。紫外扫描测定含量分别为7.17%,7.31%和51.8%。用生物素-CaM覆盖法检测到3种CaM结合蛋白,与SDS-PAGE结果一致。酶活性测定实验表明在蚯蚓CaMBPs中有Ca2+-ATPase活性,但无NAD激酶活性。  相似文献   

12.
IntroductionLanthanide (Ln3 )can promotethegrowthofcropsandincreasetheirproduction .However ,Ln3 canalsoaffectanimaltissuesandhassometoxicfunctionsatcertainconcentrations[1] .ThemechanismbywhichLn3 exertsbiologicaleffectsremainsunclear.StudiesshowthatLn3 cani…  相似文献   

13.
莴苣(挂丝红品种)种子萌发过程中,内源亚精胺(Spd)含量逐渐增加.Ca2+通道抑制剂Co2+和L3+、钙调素(CaM)拮抗剂氯两嗪(CPZ)处理抑制种子内源亚精胺含量的增加,Ca2+可部分逆转Co2+和La3+的抑制效应.外源亚精胺处理能部分逆转Co2+和La3+对萌发的抑制效应.表明Ca2+和CaM对种子萌发的调节作用与其对亚精胺含量的影响有关.  相似文献   

14.
Schumacher MA  Rivard AF  Bächinger HP  Adelman JP 《Nature》2001,410(6832):1120-1124
Small-conductance Ca2+-activated K+ channels (SK channels) are independent of voltage and gated solely by intracellular Ca2+. These membrane channels are heteromeric complexes that comprise pore-forming alpha-subunits and the Ca2+-binding protein calmodulin (CaM). CaM binds to the SK channel through the CaM-binding domain (CaMBD), which is located in an intracellular region of the alpha-subunit immediately carboxy-terminal to the pore. Channel opening is triggered when Ca2+ binds the EF hands in the N-lobe of CaM. Here we report the 1.60 A crystal structure of the SK channel CaMBD/Ca2+/CaM complex. The CaMBD forms an elongated dimer with a CaM molecule bound at each end; each CaM wraps around three alpha-helices, two from one CaMBD subunit and one from the other. As only the CaM N-lobe has bound Ca2+, the structure provides a view of both calcium-dependent and -independent CaM/protein interactions. Together with biochemical data, the structure suggests a possible gating mechanism for the SK channel.  相似文献   

15.
The effect of La^3 on potassium channels in rat ventricular myocytes was investigated using the whole-cell patch-clamp recording mode. The Ca^2 -independent voltage-activated outward K~ current was activated by the depolar-izing pulse in enzymatically isolated rat ventricular myocytes. After addition of different concentrations La^3 to the bath solution, the outward K^ current was depressed gradually. The inhibition effect was in a concentration-dependent manner. The phenomena of the outward K^ current, being themain repolarizing current suppressed by La^3 , suggest that the effect of lanthanides on myocardial function should be exploited further.  相似文献   

16.
DeMaria CD  Soong TW  Alseikhan BA  Alvania RS  Yue DT 《Nature》2001,411(6836):484-489
Acute modulation of P/Q-type (alpha1A) calcium channels by neuronal activity-dependent changes in intracellular Ca2+ concentration may contribute to short-term synaptic plasticity, potentially enriching the neurocomputational capabilities of the brain. An unconventional mechanism for such channel modulation has been proposed in which calmodulin (CaM) may exert two opposing effects on individual channels, initially promoting ('facilitation') and then inhibiting ('inactivation') channel opening. Here we report that such dual regulation arises from surprising Ca2+-transduction capabilities of CaM. First, although facilitation and inactivation are two competing processes, both require Ca2+-CaM binding to a single 'IQ-like' domain on the carboxy tail of alpha1A; a previously identified 'CBD' CaM-binding site has no detectable role. Second, expression of a CaM mutant with impairment of all four of its Ca2+-binding sites (CaM1234) eliminates both forms of modulation. This result confirms that CaM is the Ca2+ sensor for channel regulation, and indicates that CaM may associate with the channel even before local Ca2+ concentration rises. Finally, the bifunctional capability of CaM arises from bifurcation of Ca2+ signalling by the lobes of CaM: Ca2+ binding to the amino-terminal lobe selectively initiates channel inactivation, whereas Ca2+ sensing by the carboxy-terminal lobe induces facilitation. Such lobe-specific detection provides a compact means to decode local Ca2+ signals in two ways, and to separately initiate distinct actions on a single molecular complex.  相似文献   

17.
A calcium sensor in the sodium channel modulates cardiac excitability.   总被引:11,自引:0,他引:11  
Sodium channels are principal molecular determinants responsible for myocardial conduction and maintenance of the cardiac rhythm. Calcium ions (Ca2+) have a fundamental role in the coupling of cardiac myocyte excitation and contraction, yet mechanisms whereby intracellular Ca2+ may directly modulate Na channel function have yet to be identified. Here we show that calmodulin (CaM), a ubiquitous Ca2+-sensing protein, binds to the carboxy-terminal 'IQ' domain of the human cardiac Na channel (hH1) in a Ca2+-dependent manner. This binding interaction significantly enhances slow inactivation-a channel-gating process linked to life-threatening idiopathic ventricular arrhythmias. Mutations targeted to the IQ domain disrupted CaM binding and eliminated Ca2+/CaM-dependent slow inactivation, whereas the gating effects of Ca2+/CaM were restored by intracellular application of a peptide modelled after the IQ domain. A naturally occurring mutation (A1924T) in the IQ domain altered hH1 function in a manner characteristic of the Brugada arrhythmia syndrome, but at the same time inhibited slow inactivation induced by Ca2+/CaM, yielding a clinically benign (arrhythmia free) phenotype.  相似文献   

18.
Voltage-dependent calcium (Ca2+) channels are involved in many specialized cellular functions, and are controlled by intracellular signals such as heterotrimeric G-proteins, protein kinases and calmodulin (CaM). However, the direct role of small G-proteins in the regulation of Ca2+ channels is unclear. We report here that the GTP-bound form of kir/Gem, identified originally as a Ras-related small G-protein that binds CaM, inhibits high-voltage-activated Ca2+ channel activities by interacting directly with the beta-subunit. The reduced channel activities are due to a decrease in alpha1-subunit expression at the plasma membrane. The binding of Ca2+/CaM to kir/Gem is required for this inhibitory effect by promoting the cytoplasmic localization of kir/Gem. Inhibition of L-type Ca2+ channels by kir/Gem prevents Ca2+-triggered exocytosis in hormone-secreting cells. We propose that the small G-protein kir/Gem, interacting with beta-subunits, regulates Ca2+ channel expression at the cell surface.  相似文献   

19.
本文通过分子对接的方法研究了香豆素类二聚体作为AChE抑制剂在正常活性位点(Set203、Glu334和His447)和外周阴离子活性位点(His287、Tyr72、Tyr441和Glu292)的作用情况.研究结果表明,此类抑制剂有两个负电性中心:抑制剂母体的内酯区和6位或7位的苄基区.由于这两部分负电作用比较强极易与周围蛋白质发生静电作用,从而导致氢键的形成.研究发现香豆素二聚体类抑制剂更容易结合在AChE的外周阴离子活性区域.这类抑制剂在外周阴离子活性位点有相同的作用模式.这使得香豆素类二聚体有可能成为一种有更好应用前景的乙酰胆碱酯酶抑制剂.  相似文献   

20.
Dick IE  Tadross MR  Liang H  Tay LH  Yang W  Yue DT 《Nature》2008,451(7180):830-834
Ca2+/calmodulin-dependent regulation of voltage-gated CaV1-2 Ca2+ channels shows extraordinary modes of spatial Ca2+ decoding and channel modulation, vital for many biological functions. A single calmodulin (CaM) molecule associates constitutively with the channel's carboxy-terminal tail, and Ca2+ binding to the C-terminal and N-terminal lobes of CaM can each induce distinct channel regulations. As expected from close channel proximity, the C-lobe responds to the roughly 100-microM Ca2+ pulses driven by the associated channel, a behaviour defined as 'local Ca2+ selectivity'. Conversely, all previous observations have indicated that the N-lobe somehow senses the far weaker signals from distant Ca2+ sources. This 'global Ca2+ selectivity' satisfies a general signalling requirement, enabling a resident molecule to remotely sense cellular Ca2+ activity, which would otherwise be overshadowed by Ca2+ entry through the host channel. Here we show that the spatial Ca2+ selectivity of N-lobe CaM regulation is not invariably global but can be switched by a novel Ca2+/CaM-binding site within the amino terminus of channels (NSCaTE, for N-terminal spatial Ca2+ transforming element). Native CaV2.2 channels lack this element and show N-lobe regulation with a global selectivity. On the introduction of NSCaTE into these channels, spatial Ca2+ selectivity transforms from a global to local profile. Given this effect, we examined CaV1.2/CaV1.3 channels, which naturally contain NSCaTE, and found that their N-lobe selectivity is indeed local. Disruption of this element produces a global selectivity, confirming the native function of NSCaTE. Thus, differences in spatial selectivity between advanced CaV1 and CaV2 channel isoforms are explained by the presence or absence of NSCaTE. Beyond functional effects, the position of NSCaTE on the channel's amino terminus indicates that CaM can bridge the amino terminus and carboxy terminus of channels. Finally, the modularity of NSCaTE offers practical means for understanding the basis of global Ca2+ selectivity.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号