共查询到20条相似文献,搜索用时 46 毫秒
1.
Christoph Syldatk Dirk Völkel Ulrich Bilitewski Karsten Krohn Hartmut Höke Fritz Wagner 《Biotechnology letters》1992,14(2):105-110
Summary Resting cells ofArthrobacter sp. (DSM 3745) with the ability to form L-tryptophan from D,L-5-(3-indolylmethy)hydantoin were used for the bioconversion of D,L-5-- and D,L-5--naphthylmethylhydantoin (D,L-5-- and D,L-5--NMH) to the corresponding L-amino acids. Under the optimal reaction conditions of pH 9.7 and 40°C specific productivities of 0.2 (-naphtylalanine) and 0.6 (-naphtylalanine) mM amino acid x g cell dry mass–1 x h–1 were obtained in a 0.1 M Na2CO3/NaHCO3-buffer in a strirred bioreactor. 相似文献
2.
Summary The angular dependence of1JC,H in model compounds related to -linked oligosaccharides has been established by FPT INDO quantum chemical calculations. Values calculated for models of (1 1)-, (1 2)-, (1 3)- and (1 4)-linked disaccharides were compared, and the effect of the orientation of HO-2 elucidated. The angular dependence of1JC,H on the torsional angles H and H and the solvent dielectric constant (s) was characterized in the form:1JC,H = A cos2+B cos + C sin2 + D since + E + Fe. The1JC,H values, measured by DEPT methods for C-1-H-1 and C-X-H-X in cellobiose, cyclic trisaccharide and hexopyranoses were used to adjust the calculated angular dependences. Based on the occurrence of the conformers for agarobiose, neoagarobiose, mannobiose and methyl -xylobioside, the thermodynamically averaged <1JC,H > values were calculated. The results obtained (<1JC-1,H-1 > 162.4, <1JC-4, H-4 > 147.6 Hz for methyl -xylobioside; <1JC-1,H-1 > 162.4 and <1JC-4,H-4] > 147.6 Hz for mannobiose; <1JC-1,H-1 > 162.8 Hz for neo agarobiose and <1JC-1,H-1 > 163.2 Hz for agarobiose) agree well with the experimental values of 162.7, 147.5, 160.4, 147.2, 160.9 and 165.7 Hz, respectively. 相似文献
3.
The C chemical shift tensors of proteins contain information on the backbone conformation. We have determined the magnitude and orientation of the C chemical shift tensors of two peptides with -helical torsion angles: the Ala residue in G*AL (=–65.7°, =–40°), and the Val residue in GG*V (=–81.5°, =–50.7°). The magnitude of the tensors was determined from quasi-static powder patterns recoupled under magic-angle spinning, while the orientation of the tensors was extracted from C–H and C–N dipolar modulated powder patterns. The helical Ala C chemical shift tensor has a span of 36 ppm and an asymmetry parameter of 0.89. Its 11 axis is 116° ± 5° from the C–H bond while the 22 axis is 40° ± 5° from the C–N bond. The Val tensor has an anisotropic span of 25 ppm and an asymmetry parameter of 0.33, both much smaller than the values for -sheet Val found recently (Yao and Hong, 2002). The Val 33 axis is tilted by 115° ± 5° from the C–H bond and 98° ± 5° from the C–N bond. These represent the first completely experimentally determined C chemical shift tensors of helical peptides. Using an icosahedral representation, we compared the experimental chemical shift tensors with quantum chemical calculations and found overall good agreement. These solid-state chemical shift tensors confirm the observation from cross-correlated relaxation experiments that the projection of the C chemical shift tensor onto the C–H bond is much smaller in -helices than in -sheets. 相似文献
4.
J. A. Ask G. Stene-Larsen K. B. Helle 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1980,139(2):109-115
Summary The atrial adrenoceptors of the rainbow trout heart (Salmo gairdneri) were characterized in spontaneously beating preparations at 8 °C.The order of affinity for the inotropic and chronotropic responses was: Isoprenaline > adrenaline salbutamol > phenylephrine noradrenaline. Selective agonists and antagonists for mammalian - and 1-adrenoceptors were without effect on the trout preparations.A potent neuronal uptake for adrenaline and noradrenaline could be demonstrated by means of cocaine blockade, consistent with considerable sympathetic innervation of the trout atrium.The results show that catecholamines increase the force and frequency of the atrium via a single, 2-type of adrenoceptor. It is suggested that there is no distinction between the innervated and the humoral -adrenoceptors in the myocardium of this species. 相似文献
5.
N. Marmiroli V. Terzi M. Odoardi Stanca C. Lorenzoni A. M. Stanca 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,73(2):190-196
Summary In barley (Hordeum vulgare L.) seedlings, a temperature step-down from 24 °C to 6°C (cold shock) determined a reduction in the incorporation of labeled aminoacids and modified the electrophoretic pattern of total proteins. At 6 °C some new proteins appeared and others were intensified (cold shock-induced proteins= CSPs); meantime, few proteins disappeared or were curtailed (cold-repressed proteins=CRPs). The majority of the proteins of the seedlings were labeled at about the same rate both at 6 °C and 24 °C, whereas at 0 °C only the cold shock proteins and a few others were detectable. The cold shock-induced variations of the protein profile differed in roots and in seed remnants which showed only some of the CSPs detected in roots. Total protein synthesis of barley genotypes Onice and Georgie, which have respectively a winter and spring growth habit, were similarly inhibited by a temperature drop. The two genotypes, however, showed some differences in the CSPs and CRPs pattern. Because Onice and Georgie have also a different thermotolerance, the hypothesis can be made that in barley specific CSPs are involved in conferring various degrees of cold resistance. 相似文献
6.
U. Rothe W. Nachtigall 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,158(6):729-737
Summary Using manometric and gas analytical methods oxygen consumption
, carbon dioxide production
, respiratory quotientRQ, (Fig. 1A-C) and thorax surface temperature difference T
ts (Fig. 3) were determined in single bees. The animals were either sitting in respiratory chambers or were suspended by the scutum, in which case they were resting, walking (turning a small polystyrene ball) or flying in a closed miniature wind tunnel.During resting (sitting in Warburg vessels) at an ambient temperatureT
a=10°C,RQ was 1.01±0.2 (n=905) with variations due to method (Fig. 1D, E).RQ values during walking were determined in single cases. In no case were they significantly different from 1.00. After the first 10 min of flight meanRQ was 1.00±0.04. It was significantly smaller than 1.00 (RQ=0.97) only during the last 5% of long-time flights (mean flight duration 58.8±28.8 min). With the exception of near-exhaustion conditions no signs of fuels other than carbohydrates were found.Metabolic rateP
m was 19.71±21.38 mW g–1 during resting at 20°CT
a30°C indicating that many resting bees actively thermoregulate at higherT
a. After excluding bees which were actively thermoregulating, by an approximationP
m was 5.65±2.44 mW g–1 at 20°CT
a30°C. True resting metabolic rate for sitting bees atT
a=10°C was 1.31±0.53 mW g–1 (Fig. 2A, B).A significant negative correlation was found between relative (specific) oxygen consumption
rel and body massM
b at 85 mgM
b150 mg.At 0°CT
ts16.5°C a significant (-0.01) positive correlation was found between
and T
ts in single resting bees:
T
Ts+0.099, or betweenP
m and T
ts:P
m=1.343 T
ts+0.581 (Fig. 3D)
in ml h–1,P
m in mW,T in °C).During walking (duration 13.15±5.71 min,n=13) at 12.5°CT
a21°C a stable T
ts of 11.41±3.37°C, corresponding to 167 mW g–1, was reached for 80 to 90% of the walking time (Fig. 4B).During wind tunnel flights of tethered animals the minimal metabolic power measured in exhaustion experiments was 240 mW g–1. Calculation of factors of increase inP
m is of limited value in poikilotherms, in which true resting conditions are not exactly defined. 相似文献
7.
H. Wendel 《European biophysics journal : EBJ》1985,11(4):239-242
Recently, we have developed an analytical, semi-microscopic theory for the macroscopic behavior of a solvent-containing black lipid film subjected to an electric cross film voltage, . Here we employ the theoretical expressions derived for the disjoining pressure, D, the film elasticity, F, and the film tension, F, to construct the stability diagram of the film, in the D-. Depending on its state (D, ), the film is stable or is prone to squeezing or bending deformations. For a monooleate film we show how the destruction of the plane film due to a periodic thickness fluctuation (squeezing) is facilitated by two mechanisms: i) lowering of D at fixed ; ii) lowering of at fixed D, provided that the film is in a stable state characterized by D<–7.03×103 dyne/cm2 and >0 mV. Bending of a low tension film (single interface tension s 0.025 dyne/cm1) can be achieved only for >170 mV and D > –8.7 × 104 dyne/cm2. Finally, we demonstrate the existence of a marginal state (
D
0
, 0) where the film is predicted to exhibit strong fluctuations both in the squeezing and in the bending mode. 相似文献
8.
Summary
Clostridium thermohydrosulfuricum 39E produced a cell-bound -glucosidase. It was partially purified 140-fold by solubilizing with Triton X-100, ammonium sulfate treatment, DEAE-Sepharose CL-6B, octyl-Sepharose and acarbose-Sepharose affinity chromatography. The optimum temperature for the action of the enzyme was at 75°C. It had a half-life of 35 min at 75°C, 110 min at 70°C and 46 h at 60°C. The enzyme was stable at pH 5.0–6.0 and had an optimum pH at 5.0–5.5. It hydrolyzed the -1,4-linkages in maltose, maltotriose, maltotetraose and maltohexaose, the rate decreasing in order of higher-sized oligosaccharides. The enzyme preparation also hydrolyzed the -1,6 linkages in isomaltose and isomaltotriose. It rapidly hydrolyzed p-nitrophenyl -d-glucoside (pNPG). The K
m values for maltose, isomaltose, panose, maltotriose, and pNPG were 1.85, 2.95, 1.72, 0.58, and 0.31 mm, respectively, at pH 5.5 and 60°C. The enzyme produced glucose from all these substrates. The enzyme preparation did not require any metal ion for activity. The -glucosidase activity was inhibited by acarbose.
Offprint requests to: B. C. Saha 相似文献
9.
Culture experiments were carried out with Acropora sp. (a branching scleractinian coral) in seawater at two pCO2 conditions (438 and 725 µatm) and two temperatures (25 and 28 °C) in order to establish the pH and temperature dependence of the boron isotopic composition of the skeleton. A clear pCO2 effect, but no temperature effect, on the coral boron isotope composition is seen. For corals cultured at normal pCO2 (438 µatm), the 11B of the skeleton was 24.0±0.2 at 25 °C, and 23.9±0.3 at 28 °C. The values of 11B measured for corals cultured at higher pCO2 (725 µatm) were lower: 22.5±0.1, and 22.8±0.1 at 25 and 28 °C, respectively. The 11B of corals cultivated at both high and normal pCO2 conditions are consistent with a dominant pH control, and are very close to that calculated from theoretical considerations. Thus, the corals do not seem to significantly alter ambient seawater for calcification with respect to pH. Co-variation between boron and carbon isotope values is explored.Communicated by: Guest Editor A. Grottoli 相似文献
10.
Seung R. Paik Ken Yokoyama Masasuke Yoshida Toshiko Ohta Yasuo Kagawa William S. Allison 《Journal of bioenergetics and biomembranes》1993,25(6):679-684
The ATPase activity of the F1-ATPase from the thermophilic bacterium PS3 is stimulated at concentrations of rhodamine 6G up to about 10 µM where 70% stimulation is observed at 36°C. Half maximal stimulation is observed at about 3 µM dye. At rhodamine 6G concentrations greater than 10 µM, ATPase activity declines with 50% inhibition observed at about 75 µM dye. The ATPase activities of the 33 and 33 complexes assembled from isolated subunits of TF1 expressed inE. coli deleted of theunc operon respond to increasing concentrations of rhodamine 6G nearly identically to the response of TF1. In contrast, the ATPase activities of the 33 and 33 complexes are only inhibited by rhodamine 6G with 50% inhibition observed, respectively, at 35 and 75 µM dye at 36°C. The ATPase activity of TF1 is stimulated up to 4-fold by the neutral detergent, LDAO. In the presence of stimulating concentrations of LDAO, the ATPase activity of TF1 is no longer stimulated by rhodamine 6G, but rather, it is inhibited with 50% inhibition observed at about 30 µM dye at 30°C. One interpretation of these results is that binding of rhodamine 6G to a high-affinity site on TF1 stimulates ATPase activity and unmasks a low-affinity, inhibitory site for the dye which is also exposed by LDAO. 相似文献
11.
Pascal Reboul Pascal George Delphine Miquel Pierre Louisot Pierre Broquet 《Glycoconjugate journal》1996,13(1):69-79
When treated with retinoic acidin vivo, C6 glioma cells show an enhancement of CMP-Neu5Ac:Gal 1–3 GalNAc-R -2,3 sialyltransferase activity. A 300kDa glycoprotein was detected by lectin affinoblotting in retinoic acid-treated C6 cells which stained weakly or not at all in control cells. Comparative studies with different lectins demonstrated that this glycoprotein contains 2,3 Neu5Ac Gal-GalNAc O-glycan moieties. Cultures in the presence of an inhibitor of O-glycan synthesis (N-acetylgalactosaminide -O-benzyl) demonstrated that enhancement of staining of the 300 kDa glycoprotein was not due to the increase of the 2,3 sialyltransferase but to thede novo synthesis of the polypeptide chain of this glycoprotein.Abbreviations RA
retinoic acid
- Neu5Ac
N-acetylneuraminic acid
- CMP-Neu5Ac
cytidine 5 monophosphosialate
- 2,3 ST
CMP-Neu5Ac:Gal 1–3 GalNAc-R -2,3 sialyltransferase
- GalNAc-O-benzyl
N-acetylgalactosaminide -O-benzyl
- Gal1-3GalNAc-O-benzyl
Galactosyl 1-3N-acetylgalactosaminide -O-benzyl
- TBS
Tris-HCl buffer 50mm pH 7.5 containing NaCl 0.15m and Tween 20 0.05%
- B1 buffer
TBS containing MgCl2 1mm, MnCl2 1mm and CaCl2 1mm 相似文献
12.
Nobuyoshi Esaki Mutsumi Watanabe Tatsuo Kurihara Kenji Soda 《Archives of microbiology》1994,161(2):110-115
-Dialkylamino acid aminotransferase was found in various fungi; this is the first evidence for the occurrence of the enzyme in eukaryotes. The enzyme was purified from Fusarium solani and shown to be composed of four subunits with an identical molecular weight of 42,000. -Aminoisobutyrate and cycloleucine served as amino donors, and pyruvate, -ketobutyrate, -ketovalerate, -ketoisovalerate, and glyoxylate as amino acceptors. The K
m values for -aminoisobutyrate and -ketobutyrate were 28 and 0.3 mM, respectively. -Ketobutyrate inhibited the enzyme noncompetitively with -aminoisobutyrate, and showed K
i value of 8 mM. The significant inhibitory effect of l-cycloserine was observed, but d-cycloserine did not inhibit the enzyme. The pH and temperature optima for transamination of -aminoisobutyrate with pyruvate were about 8.0 and 60°C, respectively. Despite the production of this enzyme by the mesophile, the enzyme was thermostable; it retained its full activity upon heating at 60°C for 30 min.Abbreviations ACPC
1-aminocyclopropane-1-carboxylic acid
- AIB
-aminoisobutyrate
- PLP
pyridoxal 5-phosphate 相似文献
13.
K. A. Foster P. J. McDermott J. D. Robishaw 《Molecular and cellular biochemistry》1991,104(1-2):63-72
The effects of culture and membrane potential on Go39 expression were examined in neonatal rat cardiac myocytes. During six days of culture, the amount of Go39 in myocytes increased six-fold. The increase in Go39 appeared to be programmed, since Go39 of rat hearts also increased in vivo within three days after birth before declining by six days after birth. Furthermore, the age of the rat from which cardiac myocytes were isolated determined the amount of Go39 that accumulated in cultured cells with myocytes from two day-old rats producing more Go39 than myocytes from six day-old rats. In addition, agents which alter membrane potential (KCl and bupivacaine) inhibited the accumulation of Go39 in cultured myocytes. In an attempt to identify the signaling pathway in which cardiac Go39 is involved, muscarinic receptor-stimulated inositol phosphate production was examined, but was found to be comparable in myocytes that had six-fold differences in Go39 content. Thus Go39 does not appear to couple muscarinic receptors to phospholipase C in rat cardiac myocytes. 相似文献
14.
R. Nagabhushanam M. M. Hanumante Miss Meena Mirajkar G. K. Kulkarni 《Hydrobiologia》1979,62(3):269-273
The brain and thoracic ganglion neurosecretory cells of the freshwater prawn, M. kistnensis displayed characteristic changes following 24 hr exposure to warm (31.0° ± 0.5°C) and cold (13.0° ±0.5°C) stress. A and B cells from the brain showed significant elevation in their nuclear diameters after warm and cold stress. Warm stress depressed whereas cold stress enhanced the neurosecretory material intensity of A cells. However, the intensity of B cells neurosecretory material remained unaltered following both treatments. On the contrary nuclear diameters of both A and B neurosecretory cell significantly decreased and an increment in neurosecretory material intensity was revealed in the thoracic ganglion of both warm and cold stressed prawns. 相似文献
15.
To evaluate the effects of midazolam on the angiokinesis of segments of rabbits' thoracic aorta stripped of endothelium and stimulated by adrenaline.Two groups of aortic rings removed from albinic rabbits anesthetized with thiopental were used (Group I – 6 animals; Group II – 12 animals), stripped of endothelium, studied in an organ chamber, perfused by Krebs-Henseleit solution. The groups were stimulated by adrenaline, recording the maximum contraction and dT/dt at 12, 36, 60 and 120. When the plateau phase was reached, the vessel was washed with perfusion solution, recording relaxation at 2, 4 and 6. When the base values were reached, Group I underwent a new adrenergic stimulus; and Group II was stimulated with midazolam and then with adrenaline, and the same values were recorded. T test was applied as a statistical analysis when two variables were studied. When studying more than two variables the Anova test was used, supplemented by the Tuckey test.Group I did not show any significant difference between the two stimuli. Group II – the midazolam significantly reduced the maximum contraction induced by adrenaline (83.01 ± 4.11%) (p < 0.01). The dT/dt was reduced at 12 (57.06 ± 8.47%), and also at 36 (70.59 ± 5.26%). There was no significance at 60 and 120 (p < 0.01).The relaxation increased significantly at all measurements – at 2-adrenaline 39.31 ± 9.60%; adrenaline/midazolam: 44.06 ± 9.62% (p < 0.05). At 4-adrenaline: 53.08 ± 8.3%; adrenaline/midazolam: 61.68 ± 8.50% (p < 0.01). At 6-adrenaline: 76.26 ± 5.45%; adrenaline/midazolam: 84.20 ± 7.96% (p < 0.01).Midazolam significantly reduced the maximum contraction obtained by the adrenergic stimulus as well as the dT/dt in the initial phases of contraction. The relaxation speed also increased. 相似文献
16.
Joseph M. Wu Stanley J. Wertheimer Behruz Eslami Joanne C. Figuereido Biswendu B. Goswami 《Bioscience reports》1985,5(12):1041-1051
Rabbit reticulocyte lysates, gel filtered on Sephadex G-25 with or without ATP (or its analogs), were preincubated at 37°C and their subsequent binding to p3A4,3-[32P]pCp was studied. Lysates filtered without ATP or in the presence of 0.1 mM 8-bromo-ATP, 1,N6-etheno-ATP, or ITP showed a time-dependent decrease in binding activity. This decrease was completely prevented when lysates were filtered with 0.1 mM ATP, 2-deoxy-ATP, --methylene-ATP, or ATP--S. The stability of binding provided by ATP or 2-deoxy-ATP analogs corresponds to a more active 2–5A dependent endonucleolytic (RNAase L) activity based on studies using [3H] viral mRNA. Chromatography on heparin-agarose showed that ATP-supplemented gel-filtered reticulocyte lysates had a different p3A4,3-[32P]pCp binding activity elution-profile than lysates gel-filtered in the absence of ATP. Covalent cross-linking of periodate-oxidized p3A4,3-[32P]pC to gelfiltered lysates, preincubated at 0°C or 37°C for 30 min, showed the following results: (1) all lysates gave a major cross-linking of the radioactive ligand to an 80 000 dalton polypeptide, regardless of the temperature of preincubation, (2) Iysates gel-filtered without ATP, with 0.1 mM ITP, or --methylene-ATP, showed a significant reduction in the cross-linking of the 80 000 dalton protein, after preincubation at 37°C for 30 min. This decrease was accompanied by an increase in the labeling of two smaller polypeptides.Abbreviations used 2 5-oligoadenylates
oligonucleotides consisting of 5-adenylic acid residues joined by a 2 5-phosphodiester linkage 相似文献
17.
Fujita K Ye LH Sato M Okagaki T Nagamachi Y Kohama K 《Molecular and cellular biochemistry》1999,202(1-2):85-90
Investigations with protein kinase C (PKC) isoform-specific antisera, revealed distinct profiles of PKC isoform content amongst pituitary tissues. Western analysis revealed the and isoforms of PKC are present in rat anterior and posterior pituitary tissue as well as in the GH3 somatomammotrophic cell line. AtT-20/D16-V corticotrophic and T3-1 gonadotrophic murine cell lines contained no PKC-. The or isoforms were undetected in any pituitary tissue. PKC activity measurements revealed Ca2+-independent PKCs in T3-1 and GH3 cells which were more sensitive to activation by phorbol-dibutyrate (PDBu) than the corresponding PKC activity found in COS cells. However, Ca2+-dependent PKC activities were of similar sensitivity to PDBu in GH3, T3-1 and COS cells, indicating that functional differences observed in PDBu-sensitivity in these cells may be due to differential activation of Ca2+-independent PKC isoforms. Moreover, substrate-specificity of these PKCs were also compared indicating that the amount of Ca2+-dependency of the observed PKC activity from the same pituitary tissue is dependent upon the substrate utilized by the PKC isotypes present. These findings explain differential sensitivities of PKC-mediated actions that have previously been observed in a range of pituitary cells. (Mol Cell Biochem 000-000, 1999) 相似文献
18.
Effect of temperature and additional carbon sources on phenol degradation by an indigenous soil <Emphasis Type="Italic">Pseudomonad</Emphasis> 总被引:3,自引:0,他引:3
A new indigenous soil bacterium Pseudomonas sp. growing on phenol and on a mixture of phenol, toluene, o-cresol, naphthalene and 1,2,3-trimethylbenzene (1,2,3-TMB) was isolated and characterized. Phylogenetic analysis suggested its classification to Pseudomonadaceae family and showed 99.8% DNA sequence identity to Pseudomonas pseudoalcaligenes species. The isolate was psychrotroph, with growth temperatures ranging from ca. 0 to 40 °C. The GC–MS structural analysis of metabolic products of phenol degradation by this microorganism indicated a possible ortho cleavage pathway for high concentrations (over 200 mg L–1) of phenol. Biodegradation rates by this species were found to be three times more effective than those previously reported by other Pseudomonas strains. The effect of temperature on phenol degradation was studied in batch cultures at temperatures ranging from 10 to 40°C and different initial phenol concentrations (up to 500mgL–1). Above 300mgL–1 of initial phenol concentration no considerable depletion was recorded at both 10 and 40°C. Maximum degradation rates for phenol were recorded at 30°C. The biodegradation rate of phenol was studied also in the presence of additional carbon sources (o-cresol, toluene, naphthalene, 1,2,3-TMB) at the optimum growth temperature and was found significantly lower by a factor of eight in respect to the strong competitive inhibition between the substrates and the more available sources of carbon and energy. The Haldane equation =m S/(KS+S+S2/KI) was found to best fit the experimental data at the optimum temperature of 30°C than the Monod equation with kinetic constants m=0.27h–1, KS=56.70mgL–1, KI=249.08mgL–1. 相似文献
19.
Yukihiko Hirai Eugene A. Permyakov Lawrence J. Berliner 《Journal of Protein Chemistry》1992,11(1):51-57
The kinetics of the partial digestion of bovine -lactalbumin (-LA) by trypsin, -chymotrypsin, and pepsin was monitored by lactose synthase activity, HPLC, and difference spectrophotometry. The relative stabilities of the various metal-bound states of -LA to trypsin and chymotrypsin at 37 and 5°C decrease in the following order: Ca(II)--LA>Zn(II), Ca(II)--LA>apo--LA. The HPLC digestion patterns of Ca(II)--LA and Zn(II), Ca(II)--LA at 5 and 37°C were similar, while the corresponding digestion patterns for apo--LA were quite different, reflecting the existence of the thermally induced denaturation states of apo--LA within this temperature region. Occupation of the first Zn(II)-binding site in Ca(II)-loaded -LA slightly alters the HPLC digestion patterns at both temperatures and accelerates the digestion at 37°C due to Zn(II)-induced shift of the thermal transition of -LA, exposing some portion of thermally denatured protein. The results suggest that the binding of Zn(II) to the first Zn(II)- (or Cu(II))-specific site does not cause any drastic changes in the overall structure of -LA. The acidic form of -LA (atpH 2.2 and 37°C) was digested by pepsin at rates similar to that for the apo- or Cu(II), Ca(II)-loaded forms by trypsin or -chymotrypsin at neutralpH. Complexation of -LA with bis-ANS affords protection against pepsin cleavage. It is suggested that the protective effects of similar small lipophilic compounds to -LA may have physiological significance (e.g., for nutritional transport).On leave from the Institute of Biological Physics, USSR Academy of Sciences, Pushchino, Moscow Region, 142292, USSR. 相似文献
20.
Peter H. Barry Peter W. Gage Dirk F. Van Helden 《The Journal of membrane biology》1979,45(3-4):245-276
Summary Measurements of acetylcholine-induced single-channel conductance and null potentials at the amphibian motor end-plate in solutions containing Na, K, Li and Cs ions (Gage & Van Helden, 1979;J. Physiol. (London) (in press) were analyzed in terms of three models. Two of these models, the neutral site channel model and the charged site channel model were developed to cater for three cations. Both were shown to be able to explain the dependence of single-channel conductance on membrane potential and gave the following sequences of equilibrium constants and mobilities.K
Li/K
Na/K
K/K
Cs=71.710.9 andu
Cs/u
K/u
Na/u
Li=1.410.580.13 at 8 °C. Similar sequences were obtained at 20 °C. Although the neutral model fitted the data for relative conductances in Li-, Cs-and Na-solutions slightly better than the charged model, experiments done in normal [NaCl] and [NaCl]/2 solutions could only be fitted by the neutral model. In contrast, the third model, the Constant Field Equation, was unable to fit the conductance data in any of the above situations. The data available suggests that permeation is through long neutral channels, lined with high field-strength negative polar groups and including one or possibly more high resistance barriers for anions. 相似文献