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1.
Freeman W. Cope 《Bulletin of mathematical biology》1965,27(3):237-252
A previously developed theory of particulate electron conduction enzymes was based on a model of an enzyme particle catalyzing the oxidation-reduction of two different substrates at two different enzymatic sites on the same particle with conduction of electrons between the two sites through the enzyme particle. Using the simplifying assumption that the percent reduction of the second substrate is held constant, there was previously shown to be a hyperbolic relationship between the first order rate constant (k′) and the sum (C x ) of oxidized plus reduced substrate, of the formk′=α/(C x +β), where α and β are positive constants. It is shown here that if this simplifying assumption is omitted, a positive constant is added to the right hand side of this equation, which describes exactly the experimental data of Smith and conrad on cytochrome oxidase. If electron transport is assumed to be coupled to ion transport, this equation becomesk′=(α/C x )?γ (where γ is a positive constant) which describes the experimental data of Eadie and Gale on pyruvic carboxylase of yeast. It seems probable that the same theory is applicable to coupled ion-ion transport and coupled electron-electron transport in both membranous systems, and in particulate preparations consisting of membrane fragments. 相似文献
2.
GABAA receptors composed of α, β and γ subunits display a significantly higher single-channel conductance than receptors comprised
of only α and β subunits. The pore of GABAA receptors is lined by the second transmembrane region from each of its five subunits and includes conserved threonines at
the 6′, 10′ and 13′ positions. At the 2′ position, however, a polar residue is present in the γ subunit but not the α or β
subunits. As residues at the 2′, 6′ and 10′ positions are exposed in the open channel and as such polar channel-lining residues
may interact with permeant ions by substituting for water interactions, we compared both the single-channel conductance and
the kinetic properties of wild-type α1β1 and α1β1γ2S receptors with two mutant receptors, αβγ(S2′A) and αβγ(S2′V). We found
that the single-channel conductance of both mutant αβγ receptors was significantly decreased with respect to wild-type αβγ,
with the presence of the larger valine side chain having the greatest effect. However, the conductance of the mutant αβγ receptors
remained larger than wild-type αβ channels. This reduction in the conductance of mutant αβγ receptors was observed at depolarized
potentials only (ECl = −1.8 mV), which revealed an asymmetry in the ion conduction pathway mediated by the γ2′ residue. The substitutions at the
γ2′ serine residue also altered the gating properties of the channel in addition to the effects on the conductance with the
open probability of the mutant channels being decreased while the mean open time increased. The data presented in this study
show that residues at the 2′ position in M2 of the γ subunit affects both single-channel conductance and receptor kinetics. 相似文献
3.
Hiroaki Nobuhara Keisuke Kuida Makoto Furutani Toshihiko Shiroishi Kazuo Moriwaki Yusuke Yanagi Tomio Tada 《Immunogenetics》1989,30(6):405-413
Southern blots of genomic DNA from 23 strains of laboratory mice and 19 individual wild mice were examined for restriction
fragment length polymorphisms in their loci encoding the T-cell receptors (Tcr): the constant regions of the α, β, and γ chains
(C
α,C
β, andC
γ) and a variable region family of the β chain (V
β8). Only a few polymorphisms were observed for each locus in the laboratory mice after using three restriction enzymes,Bam HI,Eco RI, andHind III. All the laboratory mice examined fall into one of two types for theC
α,C
β andV
β8 loci and one of three types for theC
γ. These types are found in some of the wild mice studied, indicating that they were already present in the founder mice of
laboratory mouse strains. In contrast, theTcr genes are highly polymorphic among wild mice. Analysis of the polymorphisms in these loci suggests that laboratory mice have
inherited their genes not only fromMus musculus domesticus, but also from other subspecies, and much more than previously believed from Asian subspecies. 相似文献
4.
Small-angle neutron scattering (SANS) on the unilamellar vesicle (ULV) populations (diameter 500 and 1,000 Å) in D2O was used to characterize lipid vesicles from dimyristoylphosphatidylcholine (DMPC) at three phases: gel Lβ′, ripple Pβ′ and liquid Lα. Parameters of vesicle populations and internal structure of the DMPC bilayer were characterized on the basis of the separated form factor (SFF) model. Vesicle shape changes from nearly spherical in the Lα phase to elliptical in the Pβ′ and Lβ′ phases. This is true for vesicles prepared via extrusion through pores with the diameter 500 Å. Parameters of the internal bilayer structure (thickness of the membrane and the hydrophobic core, hydration and the surface area of the lipid molecule) were determined on the basis of the hydrophobic–hydrophilic (HH) approximation of neutron scattering length density across the bilayer ρ(x) and of the step function (SF) approximation of ρ(x). DMPC membrane thickness in the Lα phase (T=30°C) demonstrates a dependence on the membrane curvature for extruded vesicles. Prepared via extrusion through 500 Å diameter pores, vesicle population in the Lα phase has the following characteristics: average value of minor semi-axis 266±2 Å, ellipse eccentricity 1.11±0.02, polydispersity 26%, thickness of the membrane 48.9±0.2 Å and of the hydrophobic core 19.9±0.4 Å, surface area 60.7±0.5 Å2 and number of water molecules 12.8±0.3 per DMPC molecule. Vesicles prepared via extrusion through pores with the diameter 1,000 Å have polydispersity of 48% and membrane thickness of 45.5±0.6 Å in the Lα phase. SF approximation was used to describe the DMPC membrane structure in Lβ′ (T=10°C) and Pβ′ (T=20°C) phases. Extruded DMPC vesicles in D2O have membrane thickness of 49.6±0.5 Å in the Lβ′ phase and 48.3±0.6 Å in the Pβ′ phase. The dependence of the DMPC membrane thickness on temperature was restored from the SANS experiment. 相似文献
5.
Kubiński K Domańska K Sajnaga E Mazur E Zieliński R Szyszka R 《Molecular and cellular biochemistry》2007,295(1-2):229-236
Protein kinase CK2 is a highly conserved Ser/Thr protein kinase that is ubiquitous among eucaryotic organisms and appears
to play an important role in many cellular functions. This enzyme in yeast has a tetrameric structure composed of two catalytic
(α and/or α′) subunits and two regulatory β and β′ subunits. Previously, we have reported isolation from yeast cells four
active forms of CK2, composed of αα′ββ′, α2ββ′, α′2ββ′ and a free α′-catalytic subunit. Now, we report that in Saccharomyces cerevisiae CK2 holoenzyme regulatory β subunit cannot substitute other β′ subunit and only both of them can form fully active enzymatic
unit. We have examined the subunit composition of tetrameric complexes of yeast CK2 by transformation of yeast strains containing
single deletion of the β or β′ regulatory subunits with vectors carrying lacking CKB1 or CKB2 genes. CK2 holoenzyme activity was restored only in cases when both of them were present in the cell. Additional, co-immunoprecypitation
experiments show that polyadenylation factor Fip1 interacts with catalytic α subunits of CK2 and interaction with beta subunits
in the holoenzyme decreases CK2 activity towards this protein substrate. These data may help to elucidate the role of yeast
protein kinase CK2β/β′ subunits in the regulation of holoenzyme assembly and phosphotransferase activity. 相似文献
6.
The recombinant β-carotene 15,15′-monooxygenase from chicken liver was purified as a single 60 kDa band by His-Trap HP and Resource Q chromatography.
It had a molecular mass of 240 kDa by gel filtration indicating the native form to be tetramer. The enzyme converted β-carotene under maximal conditions (pH 8.0 and 37°C) with a k
cat of 1.65 min−1 and a K
m of 26 μM and its conversion yield of β-carotene to retinal was 120% (mol mol−1). The enzyme displayed catalytic efficiency and conversion yield for β-carotene, β-cryptoxanthin, β-apo-8′-carotenal, β-apo-4′-carotenal, α-carotene and γ-carotene in decreasing order but not for zeaxanthin, lutein, β-apo-12′-carotenal and lycopene, suggesting that the presence of one unsubstituted β-ionone ring in a substrate with a molecular weight greater than C30 seems to be essential for enzyme activity. 相似文献
7.
Masłyk M Kochanowicz E Zieliński R Kubiński K Hellman U Szyszka R 《Molecular and cellular biochemistry》2008,312(1-2):61-69
Since Svf1 is phosphoprotein, we investigated whether it was a substrate for protein kinase CK2. According to the amino acid
sequence Svf1 harbours 20 putative CK2 phosphorylation sites. Here, we have reported cloning, overexpression, purification
and characterization of yeast Svf1 as a substrate for three forms of yeast CK2. Svf1 serves as a substrate for both the recombinant
CK2α (K
m 0.35 μM) and CK2α′ (K
m 0.18 μM) as well as CK2 holoenzyme (K
m 1.1 μM). Different K
m values argue that CK2β(β′) subunit has an inhibitory effect on the activity of both CK2α and CK2α′ towards surviving factor
Svf1. Reconstitution of α′2ββ′ isoform of CK2 holoenzyme shows that β/β′ subunits have regulatory effect depending on the kind of CK2 catalytic subunit.
This effect was not observed in the case of α2ββ′ isoform, which may be due to interaction between Svf1 and regulatory CK2β subunit (shown by co-immunoprecipitation experiments).
Interactions between CK2 subunits and Svf1 protein may have influence on ATP as well as ATP-competitive inhibitors (TBBt and
TBBz) binding. CK2 phosphorylates up to six serine residues in highly acidic peptide K199EVIPESDEEESSADEDDNEDEDEESGDSEEESGSEEESDSEEVEITYED248 of the Svf1 protein in vitro. Presented data may help to elucidate the role of protein kinase CK2 and Svf1 in the regulation
of cell survival pathways. 相似文献
8.
By the use of the Immobiline technique at pH ranges 7.0–7.6 and 6.9–7.9, 16 different hemoglobin (Hb) phenotypes were observed
in 61 English Saanen goats. They are explained in this breed by a genetic theory of five β-globin genes (A
4,A
6,A
8,E, andD) and two closely linked α-globin loci (′α and ″α) of which the ″α has a variant allele, provisionally called ″α
X
. Family data together with observed and expected Hb frequencies were in agreement with the genetic theory. Among six Barbary
sheep there were three Hb phenotypes explained by the occurrence of the β-chain allelesB andC
na. 相似文献
9.
An extension to HN(CO-α/β-N,Cα-J)-TROSY (Permi and Annila in J Biomol NMR 16:221–227, 2000) is proposed that permits the simultaneous determination of the four coupling constants 1
J
N′(i)Cα(i), 2
J
HN(i)Cα(i), 2
J
Cα(i−1)N′(i), and 3
J
Cα(i−1)HN(i) in 15N,13C-labeled proteins. Contrasting the original scheme, in which two separate subspectra exhibit the 2
J
CαN′ coupling as inphase and antiphase splitting (IPAP), we here record four subspectra that exhibit all combinations of inphase
and antiphase splittings possible with respect to both 2
J
CαN′ and 1
J
N′Cα (DIPAP). Complementary sign patterns in the different spectrum constituents overdetermine the coupling constants which can
thus be extracted at higher accuracy than is possible with the original experiment. Fully exploiting data redundance, simultaneous
2D lineshape fitting of the E.COSY multiplet tilts in all four subspectra provides all coupling constants at ultimate precision.
Cross-correlation and differential-relaxation effects were taken into account in the evaluation procedure. By applying a four-point
Fourier transform, the set of spectra is reversibly interconverted between DIPAP and spin-state representations. Methods are
exemplified using proteins of various size. 相似文献
10.
P. Bhattacharya 《Journal of biosciences》1999,24(4):441-444
Accumulation of immunoglobulin Ig RNA (from several loci viz., CH, Cα, Jk-Ck and Sμ during Igμ isotype switching) in B cells and T cell receptor (TCR) RNAs (α, β andγ) in T cells of unusual sizes emanating from germline and rearranged genes were reported to accumulate in human and mouse
(and murine too). The precise mechanism and function of these sterile RNA species are yet to be delineated. Similar accumulation
of RNA species of unusual sizes were identified with DNA-RNA hybridization and isolation of cDNA employing with DNA and antibody
probes in mouse hybridoma, murine tumour, non-human primate marmoset tumour and human leukemic cells. 相似文献
11.
P2X1 receptors, the major subtype of P2X receptors in the vascular smooth muscle, are essential for α,β-methylene adenosine 5′-triphosphate
(α,β-MeATP)-induced vasoconstriction. However, relative physiological significance of P2X1 receptor-regulated vasoconstriction in the different types of arteries in the rat is not clear as compared with α1-adrenoceptor-regulated vasoconstriction. In the present study, we found that vasoconstrictive responses to noncumulative
administration of α,β-MeATP in the rat isolated mesenteric arteries were significantly smaller than those to single concentration
administration of α,β-MeATP. Therefore, we firstly reported the characteristic of α,β-MeATP-regulated vasoconstrictions in
rat tail, internal carotid, pulmonary, mesenteric arteries, and aorta using single concentration administration of α,β-MeATP.
The rank order of maximal vasoconstrictions for α,β-MeATP (E
max·α,β-MeATP) was the same as that of maximal vasoconstrictions for noradrenaline (E
max·NA) in the internal carotid, pulmonary, mesenteric arteries, and aorta. Moreover, the value of (E
max·α,β-MeATP/E
max·KCl)/(E
max·NA/E
max·KCl) was 0.4 in each of the four arteries, but it was 0.8 in the tail artery. In conclusion, P2X1 receptor-mediated vasoconstrictions are equally important in rat internal carotid, pulmonary, mesenteric arteries, and aorta,
but much greater in the tail artery, suggesting its special role in physiological function. 相似文献
12.
Stephen J. Headey Amelia Vom Jamie S. Simpson Martin J. Scanlon 《Biomolecular NMR assignments》2008,2(1):93-96
Ketopantoate reductase is an essential enzyme for pantothenate (vitamin B5) synthesis and a potential antibiotic target. Here we report the 15N and 1HN, 13C′, 13Cα and 13Cβ chemical shift assignments of the 34 kDa ketopantoate reductase in its apo state. 相似文献
13.
Xu-De Wang Xian-En Zhang Yong-Chao Guo Zhi-Ping Zhang Zhu-An Cao Ya-Feng Zhou 《Biotechnology letters》2009,31(5):711-717
The gdh and gdhr genes, encoding B12-dependent glycerol dehydratase (GDH) and glycerol dehydratase reactivase (GDHR), respectively, in Klebsiella pneumoniae, were cloned and expressed in E. coli. Part of the β-subunit was lost during GDH purification when co-expressing α, β and γ subunit. This was overcome by fusing
the β-subunit to α- or γ-subunit with/without the insertion of a linker peptide between the fusion moieties. The kinetic properties
of the fusion enzymes were characterized and compared with wild type enzyme. The results demonstrated that the fusion protein
GDHALB/C, constructed by linking the N-terminal of β-subunit to the C-terminal of α subunit through a (Gly4Ser)4 linker peptide, had the greatest catalytic activity. Similar to the wild-type enzyme, GDHALB/C underwent mechanism-based
inactivation by glycerol during catalysis and could be reactivated by GDHR.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
The effect of high salt stress on PS II heterogeneity was investigated in wheat (Triticum aestivum) leaves. On the basis of antenna size, PS II has been classified into three forms, i.e., α, β, and γ centers while on the
basis of electron transport properties of the reducing side of the reaction centers, two distinct forms of PS II have been
suggested, i.e., QB reducing centers and QB non-reducing centers. The chlorophyll a (Chl a) fluorescence transients, which can quantify PS II behavior, were recorded using PEA to derive OJIP in vivo with high time
resolution and further analyzed according to JIP test. Our results showed that with an increase in the salt concentration
during growth, the number of QB non-reducing centers increased. In antenna size heterogeneity the number of β and γ centers increased while the number of
α centers decreased. A change in the energetic connectivity between the PS II units was also observed. Recovery studies showed
that antenna heterogeneity was completely recovered from damage at 0.5 M NaCl concentration and partially recovered at 1 M
NaCl concentration while reducing side heterogeneity showed no recovery at all after 0.5 M onwards. 相似文献
15.
16.
17.
Srinivasulu S Perumalsamy K Upadhya R Manjula BN Feiring S Alami R Bouhassira E Fabry ME Nagel RL Acharya AS 《The protein journal》2006,25(7-8):503-516
The linkage of pair-wise interactions of contact site mutations of HbS has been studied using Le Lamentin [His-20 (α)→Gln], Hoshida [Glu-43 (β)→Gln] and α2β2T87Q mutations as the prototype of three distinct classes of contact sites of deoxy HbS fiber. Binary mixture experiments established that βA-chain with the Thr-87 (β)→Gln mutation is as potent as the γ-chain of HbF (α2γ2) in inhibiting polymerization. On combining the influence of Le Lamentin mutation with that of β2T87Q mutations; the net influence is only partial additivity. On the other hand, in binary mixture studies, combined influence of Hoshida mutation with that of β2T87Q mutations is synergistic. Besides, a significant level of synergistic complementation is also seen when the Le Lamentin and Hoshida mutations are combined in HbS (symmetrical tetramers). Le Lamentin and Hoshida mutation introduced into the cis-dimer of the asymmetric hybrid tetramer completely neutralizes the Val-6 (β) dependent polymerization. Accordingly, we propose that combining the perturbation of intra-double strand contact site with that of an inter-double strand contact site exhibit synergy when they are present in two different chains of the αβ dimer. A comparison of the present results with that of the earlier studies suggest that when the two contact site perturbations are from the same sub-unit of the αβ dimer only partial additivity is observed. The map of interaction linkage of the contact site mutations exposes new strategies in the design of novel anti-sickling Hbs for the gene therapy of sickle cell disease. 相似文献
18.
Małgorzata A. Broda Barbara Rzeszotarska 《International journal of peptide research and therapeutics》1998,5(5-6):441-443
Summary α,β-Dehydroamino acids are useful peptide modifiers. However, their stereoelectronic properties still remain insufficiently
recognized. Based on FTIR experiments in the range ofv
s(N-H), AI, AII andv
s(Cα=Cβ) and ab initio calculations with B3LYP/6–31G*, we studied the solution conformational preferences and the amide electron
density perturbation of Ac-ΔXaa-NHMe, where ΔXaa=ΔAla, (E)-ΔAbu, (Z)-ΔAbu, (Z)-ΔLeu, (Z)-ΔPhe and ΔVal. Each of these dehydroamides adopts a C5 structure, which in Ac-ΔAla-NHMe is fully extended and accompanied by the strong C5 hydrogen bond. Interaction with bond Cα=Cβ lessens the amidic resonance within the flanking amide groups. TheN-terminal C=O bond is noticeably shorter, both amide bonds are longer than the corresponding bonds in the saturated entities
and the N-terminal amide system is distorted. Ac-ΔAla-NHMe constitutes an exception. ItsC-terminal amide bond is shorter than the standard one and both amide systems are ideally planar. Ac-(E)-ΔAbu-NHMe shares stereoelectronic features with both Ac-ΔAla-NHMe and (Z)-dehydroamides. 相似文献
19.
PA28 subunits of the mouse proteasome: primary structures and chromosomal localization of the genes 总被引:2,自引:0,他引:2
The 20S proteasome is a multi-subunit protease responsible for the production of peptides presented by major histocompatibility
complex (MHC) class I molecules. Recent evidence indicates that an interferon-γ (IFN-γ)-inducible PA28 activator complex enhances
the generation of class I binding peptides by altering the cleavage pattern of the proteasome. In the present study, we determined
the primary structures of the mouse PA28 α- and β-subunits. The deduced amino acid sequences of the α- and β-subunits were
49% identical. We also determined the primary structure of the mouse PA28 γ-subunit (Ki antigen), a protein of unknown function
structurally related to the α- and β-subunits. The amino acid sequence identity of the γ-subunit to the α- and β-subunits
was 40% and 32%, respectively. Interspecific backcross mapping showed that the mouse genes coding for the α- and β-subunits
(designated Psme1 and Psme2, respectively) are tightly linked and map close to the Atp5g1 locus on chromosome 14. Thus, unlike the LMP2 and LMP7 subunits, the IFN-γ-inducible subunits of PA28 are encoded outside
the MHC. The gene coding for the γ-subunit (designated Psme3) was mapped to the vicinity of the Brca1 locus on chromosome 11. A computer search of the DNA databases identified a γ-subunit-like protein in ticks and Caenorhabditis elegans, the organisms with no adaptive immune system. It appears that the IFN-γ-inducible α- and β-subunits emerged by gene duplication
from a γ-subunit-like precursor.
Received: 11 March 1997 相似文献
20.
To investigate how excess excitation energy is dissipated in a ribulose-1,5-bisphospate carboxylase/oxygenase activase antisense
transgenic rice with net photosynthetic rate (P
N) half of that of wild type parent, we measured the response curve of P
N to intercellular CO2 concentration (C
i), electron transport rate (ETR), quantum yield of open photosystem 2 (PS2) reaction centres under irradiation (Fv′/Fm′), efficiency of total PS2 centres (ΦPS2), photochemical (qP) and non-photochemical quenching (NPQ), post-irradiation transient increase in chlorophyll (Chl) fluorescence (PITICF), and
P700+ re-reduction. Carboxylation efficiency dependence on C
i, ETR at saturation irradiance, and Fv′/Fm′, ΦPS2, and qP under the irradiation were significantly lower in the mutant. However, NPQ, energy-dependent quenching (qE), PITICF, and P700+ re-reduction were significantly higher in the mutant. Hence the mutant down-regulates linear ETR and stimulates cyclic electron
flow around PS1, which may generate the ΔpH to support NPQ and qE for dissipation of excess excitation energy. 相似文献