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排序方式: 共有1612条查询结果,搜索用时 15 毫秒
1.
2.
V Fonseca P Daumas L Ranjalahy-Rasoloarijao F Heitz R Lazaro Y Trudelle O S Andersen 《Biochemistry》1992,31(23):5340-5350
In order to understand how aromatic residues modulate the function of membrane-spanning proteins, we examined the role of the four tryptophans in gramicidin A (gA) in determining the average duration and permeability characteristics of membrane-spanning gramicidin channels; the tryptophan residues were replaced by tyrosine (gramicidin T, gT), tyrosine O-benzyl ether [gramicidin T(Bzl), gT(Bzl)], naphthylalanine (gramicidin N, gN), and phenylalanine (gramicidin M enantiomer, gM-). These analogues form channels with durations and conductances that differ some 10- and 16-fold, respectively. The single-channel conductance was invariably decreased by the Trp----Yyy replacement, and the relative conductance alterations were similar in phosphatidylcholine (DPhPC) and monoglyceride (GMO) bilayers. The duration variations exhibited a more complex pattern, which was quite different in the two membrane environments: in DPhPC bilayers, gN channels have an average duration that is approximately 2-fold longer than that of gA channels; in GMO bilayers, the average duration of gN channels is about one-tenth that of gA channels. The sequence-dependent alterations in channel function do not result from alterations in the channels' peptide backbone structure, because heterodimers can form between the different analogues and gramicidine A, and there is no energetic cost associated with heterodimer formation [cf. Durkin, J. T., Koeppe, R. E., II, & Andersen, O. S. (1990) J. Mol. Biol. 211, 221]. The alterations in permeability properties are consistent with the notion that Trp residues alter the energy profile for ion permeation through long-range electrostatic interactions. 相似文献
3.
M. H. L. Ribeiro D. M. F. Prazeres J. M. S. Cabral M. M. R. da Fonseca 《Bioprocess and biosystems engineering》1995,12(1-2):95-102
l-tryptophan was produced froml-serine and indole by immobilized Escherichia coli cells in organic-aqueous systems. Selective adsorption was the method chosen to enable both product separation andl-serine reutilization. Amongst various adsorbents tested activated carbons and neutral polymeric resins (XAD-4 and XAD-7) showed good performance. The neutral resins could selectively concentrate thel-tryptophan from dilute aqueous solutions and adsorbed only 5% of the unconvertedl-serine. High separation factors (l-tryptophan/l-serine and indole/l-tryptophan) were obtained with these adsorbents. Despite a lower capacity, the XAD-7 resin had the advantage of desorbingl-tryptophan with basic or acidic solutions, while organic solvents were required to desorb, at the same concentration levels, this compound from XAD-4.In a packed bed column filled with XAD-4 resin or activated carbon, totall-tryptophan adsorption and recovery were achieved at linear velocities up to 5.0 cm/min and 3.2 cm/min respectively. Successive sorbent reutilization, following continuous sorption and elution steps, was carried out in packed bed columns with the neutral resins and activated carbon.Thel-form of tryptophan, after crystallization, was identified by HPTLC.List of Symbols HPLC
High Performance Liquid Chromatography
- HPTLC
High Performance Thin Layer Chromatography
- Trp
tryptophan
- Ser
Serine
-
A
amount of sorbent(g)
-
c
equilibrium solute concentration in the aqueous phase (g/dm3)
-
c
i
initial (before adding the sorbent) liquid phase concentration (g/dm3)
-
C
T
tryptophan concentration in the inlet solution (g/dm3)
-
C
To
tryptophan concentration in the outlet solution (g/dm3)
-
E
z
axial dispersion coefficient (m2/s)
-
k
experimental constant (Eq. 1, 2 and 3)
-
K
1
rate constant of adsorption (min–1)
-
L
column length(m)
-
n
experimental constant (eq. 1, 2 and 3)
-
q
equilibrium solid phase concentration (g solute/g sorbent)
-
q
max
maximum capacity of sorbent (g solute/g sorbent)
-
t
time(s)
-
v
liquid velocity (m/s)
-
V
volume of liquid phase(dm3)
-
V
e
eluted volume(dm3)
-
V
r
volume needed to saturate the column (dm3) 相似文献
4.
The growth of four strains of the shiitake mushroom Lentinus edodes in solid substrate fermentation in synthetic oak sawdust logs was studied over a 14-week period. Total extracellular phenol oxidase activity and soluble protein were monitored and biomass estimated as the ergosterol content of the fermented sawdust. It was observed that two of the strains had a similar pattern of phenol oxidase activity with two cycles with maxima at 2 and 8 weeks of mycelial growth prior to fruiting. With the other two strains there was a maximum at week 4. For each strain, phenol oxidase activity increased with the cold shock used to induce fruiting. Phenol oxidase activity was not found to be correlated with either soluble protein or total fungal biomass in the fermented sawdust, which were correlated for each strain. Quantification of biomass from submerged liquid culture on the basis of dry weight and ergosterol contents showed that the strains fell into the same two groups with respect to the ergosterol to biomass ratio, which was markedly lower than that for a strain of L. lepideus.Correspondence to: B. C. Okeke 相似文献
5.
V. R. Lunge N. Ikuta A. S. K. Fonseca D. Hirigoyen M. Stoll S. Bonatto L. S. Ozaki 《World journal of microbiology & biotechnology》1994,10(6):648-652
Genomic DNA of 13 Bradyrhizobium japonicum strains was prepared and analysed by restriction fragment length polymorphism (RFLP) with nif and nod probes, and by random amplified polymorphic DNA (RAPD) with 11 primers of arbitrary nucleotide sequence. Polymorphism was observed in both analyses. The RFLP and RAPD banding patterns of different strains were used to calculate genetic divergence and to construct phylogenetic trees, allowing studies on the relationships between the strains. RFLP with nif and nod probes permitted the separation of the strains into two divergent groups, whereas RAPD separated them into four main groups. RAPD allowed closely related strains to be distinguished. 相似文献
6.
Maria Ieda Siqueira Linhares Yoshito Eizuru Gildete Patriota de Andrade Ivailda Barbosa Fonseca Luiz Bezerra Carvalho Ivanildo Tenorio Moreira Yoichi Minamishima 《Microbiology and immunology》1994,38(6):475-478
The seroprevalence of human T cell leukemia virus type 1 (HTLV-1) infection was investigated in Brazilians (570): native inhabitants (298) and descendants from Japanese (272) living in Recife and its neighborhoods—North-east of Brazil. Furthermore, polytransfused renal transplanted patients (54) were also examined for the serological status to this virus. The seropositivity to HTLV-1, screened by enzyme-linked immunosorbent assay (ELISA), was low: 1.34% for the local population and 0.73% for the descendants from Japanese. However, the seropositivity for the renal transplanted patients was found to be 11.1%. This higher value suggests that this retrovirus infection seems to be of importance in this clinical condition. 相似文献
7.
Summary Major analytical problems were encountered while carrying out the lipase catalyzed glycerolysis of olive oil in n-hexane. Since direct quantification of monoglycerides could not be achieved, an alternative methodology is proposed: the estimation of monoglyceride production from a mass balance after having assayed for the unconverted triolein, as well as for the diolein and free fatty acids formed. 相似文献
8.
For several species of lepidoptera, most of the approximately 350-bp
mitochondrial control-region sequences were determined. Six of these
species are in one genus, Jalmenus; are closely related; and are believed
to have undergone recent rapid speciation. Recent speciation was supported
by the observation of low interspecific sequence divergence. Thus, no
useful phylogeny could be constructed for the genus. Despite a surprising
conservation of control-region length, there was little conservation of
primary sequences either among the three lepidopteran genera or between
lepidoptera and Drosophila. Analysis of secondary structure indicated only
one possible feature in common--inferred stem loops with higher-than-random
folding energies-- although the positions of the structures in different
species were unrelated to regions of primary sequence similarity. We
suggest that the conserved, short length of control regions is related to
the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In
addition, determination of flanking sequences for one Jalmenus species
indicated (i) only weak support for the available model of insect 12S rRNA
structure and (ii) that tRNA translocation is a frequent event in the
evolution of insect mitochondrial genomes.
相似文献
9.
10.
Gustavo A. Bouchardet da Fonseca Thomas E. Lacher Jr. 《Primates; journal of primatology》1984,25(4):441-449
We report the exudate feeding behavior of two groups of marmosets (Callithrix jacchus penicillata) living permanently in Cerradão, a common woodland formation of Central Brazil. Cerradão is an open canopy formation and marmosets must occasionally descend to the ground in order to move from tree to tree. Even in atypical habitat, exudate eating is the predominant foraging activity. Marmosets are engaged in exudate collection over 70% of the total time spent feeding. They were observed gnawing on seven species of trees, and consumed exudates from four of these species. We compared the degree of utilization of the exudate sources, and examined a number of different characteristics of the exudates. Morphological adaptations that allow for the exploitation of the “exudate-eater niche” may be an important component of the adaptability ofCallithrix marmosets. 相似文献