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1.
Taichi Usui Masahiro Suzuki Toshinari Sato Hirokazu Kawagishi Kyoko Adachi Hiroshi Sano 《Glycoconjugate journal》1994,11(2):105-110
Transmannosylation from mannotriose (Man1-4Man1-4Man) to the 4-position at the nonreducing end N-acetylglucosaminyl residue ofN,N-diacetylchitobiose was regioselectively induced through the use of -d-mannanase fromAspergillus niger. The enzyme formed the trisaccharide Man1-4GlcNAc1-4GlcNAc (3.7% of the enzyme-catalysed net decrease ofN,N-diacetylchitobiose) from mannotriose as a donor andN,N-diacetylchitobiose as an acceptor. Mannobiose (Man1-4Man) was also shown to be useful as a donor substrate for the desired trisaccharide synthesis.Abbreviations Man
d-mannose
- (M
n) (n=1–5)
-linkedn-mer of mannose
- GlcNAc2
2-acetamido-2-deoxy--d-glucopyranosyl-(1–4)-2-acetamido-2-deoxy-d-glucose 相似文献
2.
We have shown that mercury affects energy transfer in Spirulina platensis. It inhibits energy transfer from phycocyanin to chlorophyll a by specifically bleaching the -84 chromophore of the chromo protein, phycocyanin (PC), in the cyanobacterium. This effect is observed during short-term exposure of cells to Hg2+ ions. Upon long-term (12 h) exposure, mercury at low concentrations (1–2.5 m) causes the gradual degradation of the polypeptide (22 kDa) of the PC of phycobilisomes in this cyanobacterium. The effect of mercury on this polypeptide is significant compared with the other phycobiliproteins. 相似文献
3.
Summary Free-living or immobilized Chlamydomonas reinhardtii cells photoproduce ammonium from nitrite in a medium containing 1 mM of l-methionine-d,l-sulphoximine (MSX). Ammonium is accumulated in the medium to 8 mM final concentration, which inhibits nitrite uptake by the MSX-treated cells and consequently the excretion of ammonium is blocked. However, if ammonium was removed from the medium and nitrite and MSX periodically restored, the photoproduction process could be maintained over 96 h, with a final ammonium concentration of about 18 mM for free-living cells and 28 mM for immobilized ones. The MSX-treated cells showed a photoproduction productivity of 1300 mol NH
4
+
· mg chlorophyll (Chl)-1, with an average production rate of 14 mol NH
4
+
· mg Chl-1 per hour, for calcium alginate-entrapped cells, while the corresponding data for free-living ones was 650 mol NH
4
+
· mg Chl-1 and 6.7 mol NH
4
+
· mg Chl-1 per hour, respectively. Immobilized cells showed a significant increase in the nitrite uptake rate, probably due to a change in membrane permeability as a consequence of cell-matrix interactions. 相似文献
4.
Marco Crisma Giovanni Valle Fernando Formaggio Vania Monaco Claudio Toniolo 《Letters in Peptide Science》1996,3(3):121-126
Summary An X-ray diffraction analysis ofZ-l-Leu-Aib-Gly-l-Ile-l-Leu-OMe, containing the N-acylated tetrapeptide amide sequence-l-Leu-Aib-Gly-l-Ile-, showed that in the crystal state the carbonyl group preceding thel-Leu1 residue acts as the acceptor of two C=OH–N intramolecular H-bonds, which give rise to an-l-Leu1-Aib2-type-III' -turn and an-l-Leu1-Aib2-Gly3-l-Ile4--turn, respectively. A second (type-I') -turn encompasses the-Aib2-Gly3-sequence. This is the third type of folding motif known for that tetrapeptide sequence, considering also those already published for the C-terminal segment of the lipopeptaibol antibiotics trichodecenin I and trichogin A IV. 相似文献
5.
Summary Several rat tissues (liver, spleen, kidney, pancreas, skin, heart, lung and brain) were shown to contain a peptidase capable of liberating naphthylamine from glycyl-dl-proline naphthylamide (Gly-Pro-NA). A single DEAE-cellulose chromatography of autodigested homogenates of the above tissues produced a partial separation of the peptidase from the enzymes hydrolysing l-leucine -naphthylamide. The Gly-Pro-NA hydrolysing enzyme was localised in tissue sections by using diazo coupling reaction and indirect immunologic techniques. Antibodies were prepared against the enzyme purified from rat liver and kidney in the rabbit. Rabbit -globulin was localized by using goat anti-rabbit -globulin labeled with fluorescein or with peroxidase. 相似文献
6.
Plant regeneration from four genotypes of weeping lovegrass (Eragrostis curvula (Schrad.) Nees), is reported via three developmental pathways: embryogenesis, organogenesis and direct regeneration. Organogenic and embryogenic callus cultures were initiated from young inflorescence segments on Murashige and Skoog's medium supplemented with 2,4-d and BA at different concentrations. The most suitable concentrations of 2,4-d for callus growth and development were 9 and 18 M combined with a BA concentration of 0.044 M. Genotypical differences were observed in the morphogenetic capacity. Direct regeneration was observed under similar culture conditions (culture medium, temperature and photoperiod) but with high light intensity (66 mol m-2 s-1). Young plants were successfully transplanted to pots and grown to maturity in the greenhouse.Abbreviations BA
benzyladenine
- 2,4-d
2,4-dichlorophenoxyacetic acid
- MS
Murashige and Skoog medium
- NAA
naphthaleneacetic acid 相似文献
7.
Rajkhowa R.C. Goswami Pranab Singh H.D. 《World journal of microbiology & biotechnology》2000,16(1):63-68
The mechanism of uptake of water-insoluble -sitosterol by a newly isolated strain of Arthrobacter
simplex SS-7 was studied. The production of an extracellular sterol-pseudosolubilizing protein during growth of A. simplex on -sitosterol was demonstrated by isolating the factor from the cell-free supernatant and its subsequent purification by Sephadex G-150 column chromatography. The M
r of the purified sterol-pseudosolubilizing protein determined by SDS–PAGE was 19kDa. The rate of sterol pseudosolubilization (5.2×10–3g l–1h–1) could not adequately account for the rate of sterol uptake (72×10–3g l–1h–1) and the specific growth rate (56×10–3 h–1). However in the unfavourable growth condition, when the cells were treated with sodium azide at the level of 30–60% of MIC, the sterol pseudosolubilization accounted for nearly 74% of the total growth containing 96% free cells. Cellular adherence to substrate particles was found to play an active role in the normal growth of the strain on -sitosterol. Unlike sodium acetate-grown cells, whose surface activity was negligible (60mNm–1), the sterol-grown cells had strong surface activity (40mNm–1). The high lipid content and long chain fatty acids in the cell-wall of -sitosterol-grown cells probably contribute to the high sterol adherence activity of the cells. 相似文献
8.
The first enzyme (named GTP cyclohydrolase) in the pathway for the biosynthesis of pteridines has been partially purified from extracts of late pupae and young adults of Drosophila melanogaster. This enzyme catalyzes the hydrolytic removal from GTP of carbon 8 as formate and the synthesis of 2-amino-4-hydroxy-6-(d-erythro-1,2,3-trihydroxypropyl)-7,8-dihydropteridine triphosphate (dihydroneopterin triphosphate). Some of the properties of the enzyme are as follows: it functions optimally at pH 7.8 and at 42 C; activity is unaffected by KCl and NaCl, but divalent cations (Mg2+, Mn2+, Zn2+, and Ca2+) are inhibitory; the K
m for GTP is 22 m; and the molecular weight is estimated at 345,000 from gel filtration experiments. Of a number of nucleotides tested, only GDP and dGTP were used to any extent as substrate in place of GTP, and these respective compounds were used only 1.8% and 1.5% as well as GTP.This work was supported by research grants from the National Institutes of Health (AM03442) and the National Science Foundation (GB33929). 相似文献
9.
Carol M. Warner Ruth M. Graves Carla M. Tollefson Mary Jo F. Schmerr Thomas J. Stephens Carmen F. Merryman Paul H. Maurer 《Immunogenetics》1976,3(1):337-348
The immune response of allophenic mice of type C57BL/6(A × SJL) F1 to GL administered in complete Freund's adjuvant was tested. Control mice of the three strains C57BL/6, A, and SJL are all nonresponders to this antigen. However, the F1 generations of C57BL/6 × A, C57BL/6 × SJL, and A × SJL were all responders to the antigen, so that the complementarity of at least two genes is confirmed. The allophenic mice showed no further complementation beyond the F1 generation, a result which may argue against the possibility that more than two genes control the response to GL in these mouse strains. Characterization of the allophenic mice over several months showed that they exhibit chimeric drift, both in their coat color and in peripheral white blood cell population. There is no apparent correlation of coat color to the lymphocyte composition of the mice at any one time. The mice are true chimeras, since killing of the two populations of white blood cells with two different anti-H-2 sera produced a 100 percent killing. The immune response of individual allophenic mice to GL showed a good correlation to the number of A × SJL lympho-cytes in the animal.Abbreviations used in this paper are GL
an amino acid polymer of 57 %l-glutamic acid, 38%l-lysine, and 5%l-phenylalanine
- GLT15
an amino acid polymer ofl-glutamic acid,l-lysine, and 15 %l-tyrosine
- (T,G)-A-L
an amino acid polymer having a polylysine backbone with side chains of polyd-l-alanine, terminating in short sequences of tyrosine and glutamic acid
- GAT10
an amino acid polymer of 60%l-glutamic acid, 30%l-alanine, and 10%l-tyrosine
- GLA5
an amino acid polymer of 57%l-glutamic acid, 38%l-lysine, and 5%l-alanine
- DNP
2,4 dinitrophenyl
- BGG
bovine gamma globulin
- FCS
fetal calf serum
- PWBC
peripheral white blood cell
- SWBC
spleen white blood cell
- T cell
thymus-derived lymphocyte
- B cell
bone marrow-derived lymphocyte 相似文献
10.
Summary According to the model of Urry, the cation-permeable gramicidin channel is a dimeric helix formed by association of two peptide monomers linked at their amino ends. In this paper the channel properties of gramicidin analogs are described which have been obtained by chemical modification at the coupling site of the two half-channels. In these analogs the amino terminal-CHO group is replaced by-CO(CH2)
n
COOH(n=2, 3, 4, 5, 6). All analogs form conducting channels in black lipid membranes with the same general properties as found for gramicidin A. The observation that the channel-forming activity decreases with increasing pH is consistent with the notion that the half-channels are linked at the amino terminus. The channel lifetime of the different analogs varies between 2 msec and 50 sec, the longest lifetime being found for the compound withn=3. The single-channel conductance is always smaller than that of gramicidin A, but the reduction of depends on the nature of the permeable ion. Ion specificity was studied at 1m electrolyte by measuring the conductance for different permeable ions (Na+, K+, Cs+). The conductance ratio(Cs+)/(Na+) was found to vary between 2 and 10.5 for the different analogs. 相似文献
11.
Acidiphilium aminolytica is proposed for a species of the genusAcidiphilium. Acidiphilium aminolytica can be phenotypically differentiated from all other species of the genusAcidiphilium. The seven strains of this species that have been studied are Gram-negative, aerobic, mesophilic, non-sporeforming, motile, and rod-shaped bacteria. They grow between pH 3.0 and 6.0, but not at pH 6.5. They yield positive results in tests for hippuric acid hydrolysis, catalase and urease production. Oxidase, esculin hydrolysis, and -galactosidase tests are negative. They can used-glucose,d-galactose, inositol, sorbitol,l-lysine,l-glutamate,l-arginine, -alanine,dl-4-aminobutyrate,dl-5-aminovalerate, sperimine, or diaminobutane as a sole carbon source, but cannot use elemental sulfur and ferrous iron as an energy source. The DNA base composition is 58.7–59.2 G+C mol%. The major isoprenoid quinone is ubiquinone with ten isoprene unit (Q-10). The major fatty acid is the C18:1 fatty acid. Two ornithine amide lipids, the C18:1 fatty acid esters of -N-3-hydroxystearylornithyltaurine and -N-3-hydroxystearylornithine, are detected as the polar aminolipid. DNA relatedness between this species and the other species ofAcidiphilium, the generaAcidomonas, andAcidobacterium was 29 to 2%. These results indicate, that this new species should be placed in the genusAcidiphilium. The type strain (strain 101) ofA. aminolytica is JCM 8796. 相似文献
12.
Summary
Vicia faba callus line (VFS 1), isolated from expiants of immature embryo, grew satisfactorily onMurashige andSkoog complete medium with 1.38 M 2,4-D, or with 0.92 M 2,4-D to which 1.0 M kinetin was added. It also grew well on the B 5 modified medium containing 2.3 M 2,4-D and 25.0 M kinetin. On the last of these media the cultures grew more uniformly and without necrosis. They also showed diminishing variation in polyploidy in favour of diploids and corresponding aneuploids (hypodiploids).After being cultured for nearly three years on MS containing 1.38 M 2,4-D, 8–33% of cultures of VFS 1 were able to regenerate roots when transferred to either MS half strength with 5.37 M NAA, or to a medium without 2,4-D, or else to media with the addition of kinetin only (in various concentrations). 相似文献
13.
Jeffrey L. Garvin Sidney A. Simon Edward J. Cragoe Jr. Lazaro J. Mandel 《The Journal of membrane biology》1985,87(1):45-54
Summary Several new amiloride analogues and two reported photoaffinity analogues were tested for irreversible inhibition of short-circuit current,I
sc, in toad bladder. Bromoamiloride, a photoaffinity analogue, induced 40% irreversible inhibition at 500 m after irradiation with ultraviolet light 320 nm. Iodoamiloride caused no irreversible inhibition. Of the new analogues tested, only 3,5-diamino-6-chloro-N-[(phenylamino) aminomethylene] pyrazinecarboxamide,phenamil, irreversibly inhibitedI
sc at concentrations of 0.05 to 5 m when added to the mucosal solution. Irreversible inhibition ofI
sc by phenamil may be attributed to specific blockage of the mucosal sodium channels, which depended on: 1) time of exposure; 2) mucosal pH: 3) mucosal sodium concentration. For example, 5 m phenamil irreversibly inhibitedI
sc by 38% in 103mm Na at pH 8.6 and nearly 75% in 30mm Na at pH 6.4 after a 40-min exposure. Irreversible inhibition occurred in two phases with time constants of 10 min and approximately 140 min. Due to its irreversible nature, phenamil may be used to measure channel density. 相似文献
14.
Dr. Michaela Šourková 《Plant Systematics and Evolution》1971,119(4-5):577-581
Zusammenfassung Die zwischen den Arten der SektionConoimorpha
Otth (UntergattungConocalyx
Willk.) der GattungSilene und den übrigen Arten derselben Gattung sowie aller übrigen Gattungen der TribusLychnideae A. Br. existierenden Unterschiede berechtigen zur Abtrennung dieser Sektion (Untergattung) als selbständige GattungPleconax
Rafin. Nach bisherigen Untersuchungen gehören in diese Gattung folgende Arten und Unterarten:Pleconax ammophila (Boiss.)ourková mit subsp.ammophila und subsp.carpathae (Chowdhuri)ourková,P. amphorina (Pomel)ourková,P. conica (L.)ourková mit subsp.conica und subsp.conomaritima (D.Jord. et P.Pan.)ourková,P. coniflora (Nees)ourková,P. conoidea (L.)ourková,P. lydia (Boiss.)ourková,P. macrodonta (Boiss.)ourková,P. multinervia (Wats.)ourková,P. sartorii (Boiss. etHeldr.)ourková,P. subconica (Friv. emend. D.Jord. et P.Pan.)ourková mit subsp.subconica und subsp.grisebachii (David.)ourková sowieP. tempskyana (Freyn etSint.)ourková. Die angeführten nomenklatorischen Umkombinationen werden hier zum ersten Male veröffentlicht. 相似文献
15.
H. N. Torres M. M. Flawiá J. A. Medrano P. Cuatrecasas 《The Journal of membrane biology》1978,43(1):19-44
Summary The kinetic behavior of the adenylyl cyclase activity associated with fat cell membranes purified by centrifugation on sucrose gradients was studied. Under most of the conditions explored, with either Mn++ or Mg++ as the divalent cation in the assay mixtures, the time courses of the reaction were not linear. In the absence of modifiers (i.e., basal activity) or in the presence of insulin, the rate tended to decrease with time; on the other hand, with fluoride or GMP-P(NH)P the curves were concave upwards. To simplify analysis of the results, two kinetic components were defined: an initial component corresponding to the transient rate measured between zero time and 1.5 min of assay and a final component corresponding to the transient rate determined between 3 and 5 min.Over the entire range of Mn++ concentration explored (0.5 to 6.0mm), the basal initial rates were slightly higher than the final ones. With Mg++ in the range between 1.5 and 2.5mm, the final rates were fourfold lower than the initial ones. Higher or lower Mg++ concentrations gave velocity ratios equivalent to those observed with Mn++.Insulin clearly decreased the final rates at Mn++ concentrations up to 2.5mm. With higher concentrations the effects were completely reversed. The effects of insulin on initial rates measured with Mn++, or the initial or final rates measured with Mg++, were less evident.Stimulation of adenylyl cyclase activity by fluoride was most pronounced on the final rates. In addition, this stimulation was higher with Mg++ than with Mn++.Isoproterenol stimulation of adenylyl cyclase was negligible in the presence of Mn++ (0.5 to 6.0mm). With Mg++ (0.5 to 6.0mm), stimulation was more evident on the final rates. *** DIRECT SUPPORT *** A0130063 00002 相似文献
16.
Sialyl Lewis X ganglioside analogues containing 4-deoxy-, 6-deoxy-, and 4,6-dideoxy-d-galactopyranose in place ofd-galactopyranose have been synthesized. Glycosylations of 2-(trimethylsilyl)ethyl 2,6-di-O-benzyl--d-galactopyranoside and 2-(trimethylsilyl)ethyl -d-fucopyranoside with the phenyl 2-thioglycoside derivative of sialic acid, usingN-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as the promoter in acetonitrile, gave the desired 2-(trimethylsilyl)ethyl sialyl--(23)--d-galactopyranoside and--d-fucopyranoside, respectively. The sialylgalactose derivative obtained was then modified to 4-deoxy and 4,6-dideoxy derivatives. These were converted, byO-benzoylation, transformation of the 2-(trimethylsilyl)ethyl group to trichloroacetimidates, and introduction of the methylthio group with methylthiomethysilane, into the corresponding glycosyl donors, which were then coupled with 2-(trimethylsilyl)ethylO-(2,3,4-tri-O-benzyl--l-fucopyranosyl)-(13)-O-(2-acetamido-6-O-benzyl-2-deoxy--d-glucopyranosyl)-(13)-2,4,6- tri-O-benzyl--d-galactopyranoside in the presence of dimethyl(methylthio)sulfonium triflate (DMTST). The resulting pentasaccharides were each converted to the corresponding -trichloroacetimidates, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the desired sphingosine derivatives. Selective reduction of the azide group,N-acylation with octadecanoic acid,O-deacylation, and saponification of the methyl ester afforded the target compounds.Synthetic Studies on Sialoglycoconjugates, Part 79. 相似文献
17.
Johannes Müthing Frank Unland Dagmar Heitmann Michaela Orlich Franz-Georg Hanisch Jasna Peter-Katalinić Vera Knäuper Harald Tschesche Sørge Kelm Roland Schauer Jürgen Lehmann 《Glycoconjugate journal》1993,10(1):120-126
The structures of gangliosides from human granulocytes were elucidated by fast atom bombardment mass spectrometry and by gas chromatography/mass spectrometry as their partially methylated alditol acetates. In human granulocytes besides GM3 (II3Neu5Ac-LacCer), neolacto-series gangliosides (IV3Neu5Ac-nLcOse4Cer, IV6Neu5Ac-nLcOse4Cer and VI3Neu5Ac-nLcOse6Cer) containing C24:1, and to some extent C22:0; and C16:0 fatty acid in their respective ceramide portions, were identified as major components. In this study we demonstrate that gangliosides from human granulocytes, the second most abundant cells in peripheral blood, can serve as receptors for influenza viruses A/PR/8/34 (H1N1), A/X-31 (H3N2), and a parainfluenza virus Sendai virus (HNF1, Z-strain). Viruses were found to exhibit specific adhesion to terminal Neu5Ac2-3Gal and/or Neu5Ac2-6Gal sequences as well as depending on the chain length of ganglioside carbohydrate backbones from human granulocytes, these important effector cells which represent the first line of defence in immunologically mediated reactions.
Abbreviations: FAB-MS, fast atom bombardment mass spectrometry; GC/EIMS, gas chromatography/electron impact mass spectrometry; GSL(s) glycosphingolipids; HPTLC, high performance thin-layer chromatography; Neu5Ac,N-acetylneuraminic acid [26], PFU, plaque forming unit. The designation of the following glycosphingolipids follows the IUPAC-IUB recommendations, and the ganglioside nomenclature system of Svennerholm was used. LacCer or lactosylceramide, Gal1-4Glc1-1Cer gangliotetraosylceramide or GgOse4Cer, Gal1-3GalNAc1-4Gal1-4Glc1-1Cer; lacto-N-tetraosylceramide or nLcOse4Cer, Gal1-4GlcNAc1-3Gal1-4-Glc1-1Cer; lacto-N-norhexaosylceramide or nLcOse6Cer, Gal1-4GlcNAc1-3Gal1-4GlcNAc1-3Gal 1-4-Glc1-1Cer; GM3, II3Neu5Ac-LacCer; GM1, II3Neu5Ac-GgOse4Cer; GD1a, IV3Neu5Ac, II3Neu5Ac-GgOse4Cer; GD1b, II3(Neu5Ac)2-GgOse4Cer; GT1b, IV3Neu5Ac, II3(Neu5Ac)2-GgOse4Cer; GQ1b, IV3(Neu5Ac)2, II3(Neu5Ac)2-GgOse4Cer; sialyllacto-N-tetraosylceramide, IV3Neu5Ac/IV6Neu5Ac-nLcOse4Cer; sialyllacto-N-norhexaosylceramide or i-active ganglioside, VI3Neu5Ac-nLcOse6Cer. 相似文献
18.
M. J. Avison S. R. Gullans T. Ogino G. Giebisch 《The Journal of membrane biology》1988,105(3):197-205
Summary Addition of glucose or the nonmetabolizable analogue -methyl-d-glucoside to rabbit proximal tubules suspended in a glucoseand alanine-free buffer caused a sustained increase in intracellular Na+ content (+43±7 nmol · (mg protein)–1) and a concomitant but larger decrease in K+ content (–72±11 nmol· (mg protein)–1). A component of the net K+ efflux was Ba2+ insensitive, and was inhibited by high (1mm) but not low (10 m) concentrations of the diuretics, furosemide and bumetanide. The increase in intracellular Na+ content is consistent with the view that the increased rates of Na+ and water transport seen in the proximal tubule in the presence of glucose can be attributed (at least in part) to a stimulation of basolateral pump activity by an increased [Na+]
i
. 相似文献
19.
Yin Kiong Hoh Hock-Hin Yeoh Teck Koon Tan 《Applied microbiology and biotechnology》1992,37(5):590-593
Summary Two extracellular -glucosidases (EC 3.2.1.21) were isolated from Aspergillus niger USDB 0827 and A. niger USDB 0828, and their physical and kinetic properties studied. Both enzymes were very similar in terms of molecular size (230000 Da), pH optimum (pH 4.6), temperature optimum (65° C), stability at high temperatures and substrate preferences. They were capable of hydrolysing -linked disaccharides, phenyl -d-glucoside, p-nitrophenyl -d-glucoside (PNPG), o-nitrophenyl -d-glucoside, salicin and methyl -d-glucoside but lacked activity towards -linked disaccharides, a range of p-nitrophenyl monoglycosides and p-nitrophenyl diglycosides. Both -glucosidases were better at hydrolysing cellobiose than cellotriose, cellotetraose or cellopentaose. For both enzymes, glucose showed competitive inhibition with PNPG as substrate but had no effect with cellobiose. However, the two -glucosidases differed in inhibition by glucono-1,5-lactone and affinity for cellobiose. -Glucosidase from A. niger USDB 0827 also gave lower specific activity, and was more susceptible to metal ions (Ag+, Fe2+ and Fe3+) inhibition than that of A. niger USDB 0828.
Correspondence to: Y. K. Hoh 相似文献
20.
Summary In the NaK-ATPase proteoliposomes (PLs), the NaK-pump activity, Na+ uptake, and ATP hydrolysis were apparently enhanced by carbonyl cyanidem-chlorophenylhydrazone (CCCP) and other ionophores without ion gradients. These ionophore effects were not cation specific. Without ionophores, the PL's ATPase activity fell to its steady-state value within 3 sec at 15°C. This decrease in activity disappeared in the presence of CCCP. Since CCCP is believed to enhance proton mobility across the lipid bilayer and dissipate membrane potential (V
m
), we postulated that aV
m
build-up partially inhibits the PLs by changing the conformation of the NaK-pump, and that CCCP eliminated this partial inhibition. Since this activation required extracellular K+ and high ATP concentration in the PLs, CCCP must affect the conversion between the phosphorylated forms of NaK-ATPase (EP); this step has been suggested by Goldschlegger et al. (1987) to be the voltage-sensitive step (J. Physiol. (London)
387:331–355). Although cytoplasmic K+ accelerated the change of ADP-and K+-sensitive EP (E*P) to K+-sensitive ADP-insensitive EP (E2P), CCCP did not compete with cytoplasmic K+ when cytoplasmic Na+ was saturated. When the PLs were phosphorylated with 20 m ATP and 20 m palmitoyl CoA instead of with high concentration of ATP, CCCP increased the E*P content and decreased the ADP-sensitive K+-insensitive EP (E1P). The results described above suggest that CCCP affects the E1P to E*P change in the E1PE*PE2P conversion and that this reaction step is inhibited byV
m
. 相似文献