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1.
Enterococcus hirae grow well under anaerobic conditions at alkaline pH (pH 8.0) producing acids by glucose fermentation. Bacterial growth was
shown to be accompanied by decrease of redox potential from positive values (~+35 mV) to negative ones (~−220 mV). An oxidizer
copper (II) ions (Cu2+) affected bacterial growth in a concentration-dependent manner (within the range of 0.05 mM to 1 mM) increasing lag phase
duration and decreasing specific growth rate. These effects were observed with the wild-type strain ATCC9790 and the atpD mutant strain MS116 (with absent β subunit of F1 of the FoF1 ATPase) both. Also ATPase activity and proton–potassium ions exchange were assessed with and without N,N′-dicyclohexylcarbodiimide (DCCD), inhibitor of the FoF1 ATPase. In both cases (DCCD ±), even low Cu2+ concentrations had noticeable effect on ATPase activity, but with less visible concentration-dependent manner. Changes in
the number of accessible SH-groups were observed with E. hirae ATCC9790 and MS116 membrane vesicles. In both strains Cu2+ markedly decreased the number of SH-groups in the presence of K+ ions. The addition of ATP increased the amount of accessible SH-groups in ATCC9790 and decreased this number in MS116; Cu2+ blocked ATP-installed increase in SH-groups number in ATCC9790. H+–K+-exchange of bacteria was markedly inhibited by Cu2+, but stronger effects were detected together with DCCD. Moreover, discrimination between Cu2+ and other bivalent cation—Ni2+ was shown. It is suggested that Cu2+ ions inhibit E. hirae cell growth by direct affect on the FoF1 ATPase leading to conformational changes in this protein complex and decrease in its activity. 相似文献
2.
Interaction of N,N′-dicyclohexylcarbodiimide (DCCD) with ATPase of Mycobacterium phlei membranes results in inactivation of ATPase activity. The rate of inactivation of ATPase was pseudo-first order for the initial 30–65% inactivation over a concentration range of 5–50 μM DCCD. The second-order rate constant of the DCCD-ATPase interaction was k = 8.5·105 M?1·min?1. The correlation between the initial binding of [14C]DCCD and 100% inactivation of ATPase activity shows 1.57 nmol DCCD bound per mg membrane protein. The proteolipid subunit of the F0F1-ATPase complex in membranes of M. phlei with which DCCD covalently reacts to inhibit ATPase was isolated by labeling with [14C]DCCD. The proteolipid was purified from the membrane in free and DCCD-modified form by extraction with chloroform/methanol and subsequent chromatography on Sephadex LH-20. The polypeptide was homogeneous on SDS-acrylamide gel electrophoresis and has an apparent molecular weight of 8000. The purified proteolipid contains phosphatidylinositol (67%), phosphatidylethanolamine (18%) and cardiolipin (8%). Amino acid analysis indicates that glycine, alanine and leucine were present in elevated amounts, resulting in a polarity of 27%. Cysteine and tryptophan were lacking. Butanol-extracted proteolipid mediated the translocation of protons across the bilayer, in K+-loaded reconstituted liposomes, in response to a membrane potential difference induced by valinomycin. The proton translocation was inhibited by DCCD, as measured by the quenching of fluorescence of 9-aminoacridine. Studies show that vanadate inhibits the proton gradient driven by ATP hydrolysis in membrane vesicles of M. phlei by interacting with the proteolipid subunit sector of the F0F1-ATPase complex. 相似文献
3.
《BBA》1986,848(2):224-229
Evidence is presented for the presence of divalent cation binding sites in purified F1-ATPase from Micrococcus lysodeikticus (Micrococcus luteus). Electron paramagnetic resonance studies of native F1-ATPase indicate that the enzyme binds Mn2+ and Cu2+. Scatchard-type plot for Mn2+ binding to the enzyme indicates the presence of 3–4 independent and identical sites with a dissociation constant of 18.3 · 10−6 M. Cu2+ binds to the enzyme at only one kind of site(s). This Cu2+ binding site(s) is characterized by a moderately ionic ligand field provided by the protein and by a tetragonal symmetry of nitrogen and/or oxigen ligands. Competition studies indicate that Mg2+ binds at these Mn2+ and Cu2+ binding sites. 相似文献
4.
Thermodynamic formation constants for the magnesium (II)-ATP and manganese (II)-ATP species have been evaluated by direct potentiometry with ion-selective liquid membrane electrodes responsive to Mg2+ and Mn2+, respectively. The existence of the second complex Mg2ATP has also been demonstrated; an evaluation of its formation constant is provided. It is shown that the ion electrode method offers advantages over earlier methods because it permits direct measurement of ion activities and, further, enables the ion of interest to be measured selectively in the presence of other ions needed to control pH and ionic strength. 相似文献
5.
Effects of prostaglandins e(2) and f(2alpha) on the electrofusion of pea mesophyll protoplasts
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The effects of prostaglandins E2 and F2α on the electrofusion of pea (Pisum sativum cv Ran 1) mesophyll protoplasts were examined. Prostaglandins E2 and F2α influenced electrofusion by lowering the threshold voltage necessary for fusion of dielectrophoretically arranged pairs of protoplasts. The direct current voltage threshold decreased with increasing Ca2+ concentration up to 0.1 millimolar CaCl2 and the effects of prostaglandins E2 and F2α were more pronounced when CaCl2 was present in the medium. Treatment with calcium channel blocker methoxy verapamil did not change the prostaglandin effects, while the addition of ethyleneglycol-bis (β-aminoethyl either)-N,N,N′,N′-tetraacetic acid, which binds free Ca2+, increased the threshold voltage. Influence of prostaglandins E2 and F2α and Ca2+ on the membrane fluidity was investigated by analysis of pyrene fluorescence spectra. The values of the ratio between the maximum fluorescence emission intensities of the excimer and the monomer forms (Iex/Imon) indicated that prostaglandins and Ca2+ decrease the membrane fluidity. It is proposed that electrically evoked displacement of plasmalemma components takes part in the fusion process (U Zimmermann 1982 Biochim Biophys Acta 694: 227-277). We suggest that prostaglandins E2 and F2α facilitate the electrofusion of pea mesophyll protoplasts by changing the fluidity of plasmalemma. 相似文献
6.
D. V. Yanykin A. A. Khorobrykh S. A. Khorobrykh N. L. Pshybytko V. V. Klimov 《Photosynthesis research》2013,117(1-3):367-374
It has been shown that removal of manganese from the water-oxidizing complex (WOC) of photosystem II (PSII) leads to flash-induced oxygen consumption (FIOC) which is activated by low concentration of Mn2+ (Yanykin et al., Biochim Biophys Acta 1797:516–523, 2010). In the present work, we examined the effect of transition and non-transition divalent metal ions on FIOC in Mn-depleted PSII (apo-WOC-PSII) preparations. It was shown that only Mn2+ ions are able to activate FIOC while other transition metal ions (Fe2+, V2+ and Cr2+) capable of electron donation to the apo-WOC-PSII suppressed the photoconsumption of O2. Co2+ ions with a high redox potential (E 0 for Co2+/Co3+ is 1.8 V) showed no effect. Non-transition metal ions Ca2+ by Mg2+ did not stimulate FIOC. However, Ca2+ (in contrast to Mg2+) showed an additional activation effect in the presence of exogenic Mn2+. The Ca2+ effect depended on the concentration of both Mn2+ and Ca2+. The Ca effect was only observed when: (1) the activation of FIOC induced by Mn2+ did not reach its maximum, (2) the concentration of Ca2+ did not exceed 40 μM; at higher concentrations Ca2+ inhibited the Mn2+-activated O2 photoconsumption. Replacement of Ca2+ by Mg2+ led to a suppression of Mn2+-activated O2 photoconsumption; while, addition of Ca2+ resulted in elimination of the Mg2+ inhibitory effect and activation of FIOC. Thus, only Mn2+ and Ca2+ (which are constituents of the WOC) have specific effects of activation of FIOC in apo-WOC-PSII preparations. Possible reactions involving Mn2+ and Ca2+ which could lead to the activation of FIOC in the apo-WOC-PSII are discussed. 相似文献
7.
Potassium ion pool was studied in glycolyzing Enterococcus hirae, grown at high or low alkaline pH (pH 9.5 and 8.0, respectively). Energy-dependent increase of K+ pool was lower for the wild-type cells, grown at pH 9.5, than that for the cells grown at pH 8.0. It was inhibited by N,N′-dicyclohexylcarbodiimide
(DCCD). The stoichiometry of DCCD-inhibited K+ influx to DCCD-inhibited H+ efflux for the wild-type cells, grown at pH 9.5 or 8.0, was fixed for different K+ external activity. DCCD-inhibited ATPase activity of membrane vesicles was significantly stimulated by K+ for the wild-type cells grown at pH 9.5, and required K+ for the wild-type cells grown at pH 8.0, while the levels of α and β subunits of the F1 and b subunit of the F0 were lower for the cells grown at pH 9.5 than that for the cells grown at pH 8.0. Such an ATPase activity was residual in
membrane vesicles from the atpD mutant with a nonfunctional F0F1. ATPase activity of membrane vesicles from the mutant with defect in Na+-ATPase was higher for the cells grown at pH 9.5 than that for the cells grown at pH 8.0, and was inhibited by DCCD. An energy-dependent
increase of K+ pool in this bacterium, grown at a high or low alkaline pH, is assumed to occur through a K+ uptaking system, most probably the Trk. The latter functions in a closed relationship with the H+-translocating ATPase F0F1.
Received: 30 June 1997 / Accepted: 4 August 1997 相似文献
8.
This paper represents H+ circles through the bacterial membranes, their peculiarities and relationship with ATP synthesis or hydrolysis, utilization or accumulation of energy are considered. Data on passive and active proton (H+) fluxes through the bacterial membranes are analyzed and their relationship with membrane H+ conductance $\left( {G_m^{H^ + } } \right)$ and permeability for H+ $\left( {P_{H^ + } } \right)$ is discussed. Methods for determination of bacterial membrane $G_m^{H^ + }$ are presented and some difficulties in obtaining and interpreting data are pointed out. Different ways and mechanisms of passive and active H+ fluxes, including a role of membrane lipids in H+ transfer, importance of phase transitions in lipid bilayers, operation of protonophores as well as H+ translocation via the F0 factor of the F0F1-ATPase, are discussed. Dependence of $G_m^{H^ + }$ for Escherichia coli, Enterococcus hirae, Streptococcus lactis and other bacteria on some external physico-chemical growth factors, particularly, on pH and oxidation reduction potential as well as influence of osmotic stress on $G_m^{H^ + }$ and H+ active fluxes through the bacterial membrane under fermentation have been shown. The relationship between $G_m^{H^ + }$ , $P_{H^ + }$ and active H+ fluxes through a membrane is proposed, possible mechanisms of relationship between their alterations depending on pH and oxidation reduction potential are discussed. The results are important for understanding the structural and functional properties of bacterial membranes determining H+ cycles operation and mechanisms of H+ fluxes essential in adaptation of bacteria to altered environment conditions. 相似文献
9.
The effects of low-intensity electromagnetic irradiation (EMI) with the frequencies of 51.8 and 53 GHz on Lactobacillus acidophilus growth and survival were revealed. These effects were compared with antibacterial effects of antibiotic ceftazidime. Decrease in bacterial growth rate by EMI was comparable with the inhibitory effect of ceftazidime (minimal inhibitory concentration—16 μM) and no enhanced action was observed with combined effects of EMI and the antibiotic. However, EMI-enhanced antibiotic inhibitory effect on bacterial survival. The kinetics of the bacterial suspension oxidation–reduction potential up to 24 h of the growth was changed by EMI and ceftazidime. The changes were more strongly expressed by combined effects of EMI and antibiotic especially up to 12 h. Moreover, EMI did not change overall energy (glucose)-dependent H+ efflux across the membrane but it increased N,N′-dicyclohexylcarbodiimide (DCCD)-inhibited H+ efflux. In contrast, this EMI in combination with ceftazidime decreased DCCD-sensitive H+ efflux. Low-intensity EMI had inhibitory effect on L. acidophilus bacterial growth and survival. The effect on bacterial survival was more significant in the combination with ceftazidime. The H+-translocating F 0 F 1-ATPase, for which DCCD is specific inhibitor, might be a target for EMI and ceftazidime. The revealed bactericide effects on L. acidophilus can be applied in biotechnology, food producing and safety technology. 相似文献
10.
The effect of Mn2+ and Ca2+ ions on the rate of trypsin autolysis was studied at pH 7.0 and at 34.4-60.2°C. For comparison, the kinetic constants of esterolytic activity of trypsin in the presence of the metal ion were determined at pH 7.4 and at 36° and 40°C. There was no significant difference in the rate of autolysis between Mn2+ and Ca2+ in the temperature range 34-47°C, but at 56.8° and 60.2° autolysis was slightly more rapid in the presence of Mn2+. The Mn2+ or Ca2+ ion bound to trypsin is supposed to control the conformation and thereby the stability and the activity of the enzyme. This indirect effect of Mn2+ and Ca2+ is discussed on a structural basis of the enzyme molecule. 相似文献
11.
D. Soghomonyan A. Margaryan K. Trchounian K. Ohanyan H. Badalyan A. Trchounian 《Cell biochemistry and biophysics》2018,76(1-2):209-217
Microorganisms are part of the natural environments and reflect the effects of different physical factors of surrounding environment, such as gamma (γ) radiation. This work was devoted to the study of the influence of low doses of γ radiation with the intensity of 2.56?μW (m2?s)?1 (absorbed doses were 3.8 mGy for the radiation of 15?min and 7.2 mGy—for 30?min) on Escherichia coli M-17 and Pseudomonas aeruginosa GRP3 wild type cells. The changes of bacterial, growth, survival, morphology, and membrane activity had been studied after γ irradiation. Verified microbiological (specific growth rate, lag phase duration, colony-forming units (CFU) number, and light microscopy digital image analysis), biochemical (ATPase activity of bacterial membrane vesicles), and biophysical (H+ fluxes throughout cytoplasmic membrane of bacteria) methods were used for assessment of radiation implications on bacteria. It was shown that growth specific rate, lag phase duration and CFU number of these bacteria were lowered after irradiation, and average cell surface area was decreased too. Moreover ion fluxes of bacteria were changed: for P. aeruginosa they were decreased and for E. coli—increased. The N,N′-dicyclohexylcarbodiimide (DCCD) sensitive fluxes were also changed which were indicative for the membrane-associated F0F1-ATPase enzyme. ATPase activity of irradiated membrane vesicles was decreased for P. aeruginosa and stimulated for E. coli. Furthermore, DCCD sensitive ATPase activity was also changed. The results obtained suggest that these bacteria especially, P. aeruginosa are sensitive to γ radiation and might be used for developing new monitoring methods for estimating environmental changes after γ irradiation. 相似文献
12.
《Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology》1996,1292(1):188-196
We studied the transition metal ion requirements for activity and sulfhydryl group reactivity in phosphoenolpyruvate carboxykinase (PEP-carboxykinase; ATP:oxaloacetate carboxylase (transphosphorylating), EC 4.1.1.49), a key enzyme in the energy metabolism of the protozoan parasite Trypanosoma (Schizotrypanum) cruzi. As for other PEP-carboxykinases this enzyme has a strict requirement of transition metal ions for activity, even in the presence of excess Mg2+ ions for the carboxylation reaction; the order of effectiveness of these ions as enzyme activators was: Co2+ > Mn2+ > Cdu2+ > Ni2+ ⪢ Fe2+ > VO2+, while Zn2+ and Ca2+ had no activating effects. When we investigated the effect of varying the type or concentration of the transition metal ions on the kinetic parameters of the enzyme the results suggested that the stimulatory effects of the transition metal center were mostly associated with the activation of the relatively inert CO2 substrate. The inhibitory effects of 3-mercaptopicolinic acid (3MP) on the enzyme were found to depend on the transition metal ion activator: for the Mn2+ activated enzyme the inhibition was purely non-competitive (Kii = Kis) towards all substrates, while for the Co2+-activated enzyme the inhibitor was much less effective, produced a mixed-type inhibition and affected differentially the interaction of the enzyme with its substrates. The modification of a single, highly reactive, cysteine per enzyme molecule by 5,5′-dithiobis(2-nitro-benzoate) (DTNB) lead to an almost complete inhibition of Mn2+-activated T. cruzi PEP-carboxykinase; however, in contrast with the results of previous studies in vertebrate and yeast enzymes, the substrate ADP slowed the chemical modification and enzyme inactivation but did not prevent it. PEP and HCO3− had no significant effect on the rate or extent of the enzyme inactivation. The kinetics of the enzyme inactivation by DTNB was also dependent on the transition metal activator, being much slower for the Co2+-activated enzyme than for its Mn2+-activated counterpart. When the bulkier but more hydrophobic reagent N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM) was used the enzyme was slowly and incompletely inactivated in the presence of Mn2+ and ADP afforded almost complete protection from inactivation; in the presence of Co2+ the enzyme was completely resistant to inactivation. Taken together, our results indicate that the parasite enzyme has a specific requirement of transition metal ions for activity and that they modulate the reactivity of a single, essential thiol group, different from the hyperreactive cysteines present in vertebrate or yeast enzymes. 相似文献
13.
Membrane-bound ATPase of Escherichia coli was released in a soluble form by decreasing the Mg2+ concentration to 0.05 mM. The particulate fraction left behind was depleted by more than 90% from its initial ATPase activity.Soluble ATPase exhibits a number of different properties as compared with membrane-bound ATPase. These are a 2-fold increased Km toward ATP, a shift of 1–1.5 pH units in the pH-dependence curve, a greatly increased resistance to inhibition by N,N′-dicyclohexylcarbodiimide (DCCD) and a stimulation by Dio 9 instead of an inhibition.Upon mixing the soluble fraction and the depleted membrane fraction, the initial properties of native membrane-bound ATPase reappear. This reconstitution requires Mg2+ and results in the physical binding of the activity to sedimentable material.Soluble ATPase and depleted membrane can be titrated against each other until an equivalence point is reached, beyond which the component in excess keeps its previous characteristics.During the release procedure, DCCD remains associated with the particulate fraction with conservation of the ATPase-binding sites.Such DCCD-treated depleted membranes behave as a specific inhibitor of soluble ATPase. 相似文献
14.
A new macrocyclic hexanuclear manganese(III) 18-azametallacrown-6 compound, [Mn6(ashz)6(CH3OH)3(H2O)3] · 3H2O · 3DMF (1), has been prepared using a trianionic pentadentate ligand N-acetylsalicylhydrazide (ashz3−) and characterised by various techniques such as elemental analysis, IR, UV-vis and fluorescence spectroscopy, cyclic voltammetry and X-ray diffraction. Six ashz3− ligands connect six metal ions to form the cyclic skeleton based on the M-N-N-M linkage. Due to the meridional coordination of the ligand to the Mn3+ ion, the ligand enforces the stereochemistry of the Mn3+ ions as a propeller configuration with alternating Δ/Λ forms. The kinetic studies on catecholase activity of 1 for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) by O2 were done using UV-Vis absorption spectra method. Compound 1 has been evaluated as a model system for the catechol oxidase enzyme and it is found that the compound shows high catecholase activity. It exhibits the activity with a turnover number of 270 h−1. A kinetic treatment on the basis of the Michaelis-Menten model has been applied. The magnetic susceptibility (300-5 K) study indicates antiferromagnetic exchange interactions with J = −2.6 cm−1 between the adjacent Mn3+ ions. 相似文献
15.
Bartolommei G Gramigni E Tadini-Buoninsegni F Santini G Moncelli MR 《Biophysical journal》2010,99(7):2087-2096
The effect of Pb2+ ions on the Na+,K+-ATPase was investigated in detail by means of steady-state fluorescence spectroscopy. Experiments were performed by using the electrochromic styryl dye RH421. It is shown that Pb2+ ions can bind reversibly to the protein and do not affect the Na+ and K+ binding affinities in the E1 and P-E2 conformations of the enzyme. The pH titrations indicate that lead(II) favors binding of one H+ to the P-E2 conformation in the absence of K+. A model scheme is proposed that accounts for the experimental results obtained for backdoor phosphorylation of the enzyme in the presence of Pb2+ ions. Taken together, our results clearly indicate that Pb2+ bound to the enzyme stabilizes an E2-type conformation. In particular, under conditions that promote enzyme phosphorylation, Pb2+ ions are able to confine the Na+,K+-ATPase into a phosphorylated E2 state. 相似文献
16.
Joseph D. Robinson 《Journal of bioenergetics and biomembranes》1985,17(3):183-200
Phosphatase activity of a kidney (Na + K)-ATPase preparation was optimally active with Mg2+ plus K+. Mn2+ was less effective and Ca2+ could not substitute for Mg2+. However, adding Ca2+ with Mg2+ or substituting Mn2+ for Mg2+ activated it appreciably in the absence of added K+, and all three divalent cations decreased apparent affinity for K+. Inhibition by Na+ decreased with higher Mg2+ concentrations, when Ca2+ was added, and when Mn2+ was substituted for Mg2+. Dimethyl sulfoxide, which favorsE
2 conformations of the enzyme, increased apparent affinity for K+, whereas oligomycin, which favorsE
1 conformations, decreased it. These observations are interpretable in terms of activation through two classes of cation sites. (i) At divalent cation sites, Mg2+ and Mn2+, favoring (under these conditions)E
2 conformations, are effective, whereas Ca2+, favoringE
1, is not, and monovalent cations complete. (ii) At monovalent cation sites divalent cations compete with K+, and although Ca2+ and Mn2+ are fairly effective, Mg2+ is a poor substitute for K+, while Na+ at these sites favorsE
1 conformations. K+ increases theK
m
for substrate, but both Ca2+ and Mn2+ decrease it, perhaps by competing with K+. On the other hand, phosphatase activity in the presence of Na+ plus K+ is stimulated by dimethyl sulfoxide, by higher concentrations of Mg2+ and Mn2+, but not by adding Ca2+; this is consistent with stimulation occurring through facilitation of an E1 to E2 transition, perhaps an E1-P to E2-P step like that in the (Na + K)-ATPase reaction sequence. However, oligomycin stimulates phosphatase activity with Mg2+ plus Na+ alone or Mg2+ plus Na+ plus low K+: this effect of oligomycin may reflect acceleration, in the absence of adequate K+, of an alternative E2-P to E1 pathway bypassing the monovalent cation-activated steps in the hydrolytic sequence. 相似文献
17.
Effect of N,N'-dicyclohexylcarbodiimide (DCCD) on electron transport particles of Mycobacterium phlei 总被引:3,自引:0,他引:3
N,N′-dicyclohexylcarbodiimide (DCCD) was found to uncouple phosphorylation from oxidation with succinate and NAD+-linked substrates in the system from Mycobacterium phlei. However, in contrast to the effect of this agent in mammalian mitochondria, DCCD was found to stimulate oxidation with succinate as an electron donor and to inhibit the oxidation of NAD+-linked substrates. Furthermore, in the M. phlei system DCCD was found to inhibit the membrane bound latent ATP-ase but had no effect on this activity when the latent ATPase was removed from the membrane vesicles. Reconstitution with the fraction containing latent ATPase activity and the membrane vesicles resulted in inhibition of latent ATPase by DCCD. Studies of the effect of DCCD on the resolved system indicated that DCCD may be associated with membrane vesicles or causes secondary changes in conformation of membrane vesicles. Although DCCD inhibited membrane bound ATPase it did not prevent the addition of the solubilized ATPase to the membrane vesicles. DCCD was found to have no effect on purified succinic dehydrogenase activity but stimulated this activity in the electron transport particles. 相似文献
18.
It was ascertained that one-hour exposure of Enterococcus hirae ATCC9790 bacteria grown under anaerobic condition during sugar (glucose) fermentation to coherent electromagnetic irradiation (EMI) of 51.8 and 53.0 GHz frequencies or millimeter waves (5.79 and 5.66 mm wavelengths) of low-intensity (flux capacity of 0.06 mW/cm2) caused a significant decrease in energy-dependent H+ and K+ transports across the membranes of whole cells. Therewith, K+ influx into cells was appreciably less at the frequency of 53.0 GHz. Likewise, a significant decrease of total and N,N′-dicyclohexylcarbodiimide-sensitive ATPase activity of the membrane vesicles occurred after EMI of 51.8 and 53.0 GHz. These results indicated the input of membranous changes in bacterial action of low intensity extremely high frequency EMI, when the F0F1-ATPase was probably playing a key role. Additionally, the enhancement of the effects of antibiotics — ceftriaxone, kanamycin and ampicillin at their minimal inhibitory concentrations (100, 200 and 1.4 μM, correspondingly) on the bacterial growth by these irradiations was shown. Also, combined action of EMI and antibiotics depressed strongly H+ and K+ fluxes across membrane. Especially, H+ flux was more sensitive to the action of ceftriaxone, but K+ flux was sensitive to kanamycin. All these made the assumption that EMI of 51.8 and 53.0 GHz frequencies, especially 53.0 GHz, was followed by change in bacterial sensitivity toward antibiotics that was more obvious with ceftriaxone and ampicillin. 相似文献
19.
J D Robinson 《Archives of biochemistry and biophysics》1982,213(2):650-657
CTP was a poorer substrate than ATP when substituted in the (Na + K)-ATPase reaction assay, not only in terms of Km but also of V. CDP was a poorer inhibitor than ADP, so product inhibition cannot account for CTP being a poorer substrate. In the Na-ATPase reaction, which the enzyme also catalyzes, substituting CTP for ATP resulted in greater activity, arguing against CTP being less effective than ATP in forming the enzyme-phosphate intermediate common to both reactions. Ligands that favor the E2 conformational state of the enzyme, K+, Mg2+, and Mn2+, inhibited the (Na + K)-CTPase reaction more than the (Na + K)-ATPase. Conversely, Triton X-100, which favors the E1 conformational state of the enzyme, K+, Mg2+, and Mn2+, inhibited the (Na + K)-CTPase ATPase reaction but stimulated the (Na + K)-CTPase. Although the (Na + K)-ATPase reaction sequence probably involves cyclical interconversion between E1 and E2 conformational states (and is thus inhibitable by ligands favoring either state), the K-phosphatase reaction catalyzed by the enzyme apparently functions entirely in the E2 state. This reaction is better stimulated by CTP plus Na+ than by ATP plus Na+; moreover, CTP lessens inhibition by Triton X-100, and ATP lessens inhibition by inorganic phosphate (which reacts with the E2 state). These observations indicate that CTP is a poorer substrate than ATP because it is less effective in promoting conversion of E2 to E1, essential for the (Na + K)-dependent reaction mechanism. However, contrary to this rationale, dimethyl sulfoxide stimulated the (Na + K)-CTPase reaction although by other criteria, including inhibition of the (Na + K)-ATPase, the reagent appears to favor the E2 over the E1 conformational state. 相似文献
20.
A fluorescent photoaffinity label—8-azido-1-N6-etheno-adenosine 5′-triphosphate (8-N3ε ATP)—for ATP-binding proteins has been synthesized. The effectiveness of the label is demonstrated with F1ATPase from Micrococcus luteus. 8-N3ε ATP is a substrate for the enzyme in the presence of bivalent cations. Ultraviolet irradiation of F1ATPase in the presence of the label and Mg2+ ions inhibits the enzyme irreversibly. The fluorescent label is bound preferentially to the β subunit of the enzyme. Labeling and inactivation are decreased by protection with ATP or ADP. 相似文献