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141.
The operational stability of the Candida rugosa lipase immobilized in a hydrophilic polyurethane foam was evaluated in consecutive batches for the glycerolysis of olive oil in n-hexane, aimed at the production of monoglycerides.Glycerol controlled the glycerolysis in the system under study, since it is both a substrate and a powerful water binder that reduces the water activity of the reaction medium and of the microenvironment. Two sets of experiments were carried out under different glycerol/triglyceride ratios. After 345 hours of consecutive 23 hours batches no lipase inactivation was observed.List of Symbols aw
thermodynamic activity of water
- DG
diglyceride (s)
- FAME
fatty acid methyl ester (s)
- FFA
free fatty acid (s)
- FID
flame ionization detector Gly glycerol
- MG
monoglyceride (s)
- TG
triglyceride (s)
- TLC
thin layer chromatography
The authors are grateful to Profs. P. Adlercreutz, Technical University of Lund, Sweden, and J.M.S. Cabral, Instituto Superior Técnico, Lisbon, Portugal, for inspiring discussions and advice, to Prof. Helena Pereira, Instituto Superior de Agronomia (ISA), Lisbon, Portugal, for the use of GC equipment and to Mrs. Marlene Dionísio, ISA, for invaluable help with some of the experimental work. 相似文献
142.
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
143.
G. Guillen M. J. Leal A. Alvarez M. Delgado R. Silva L. Herrera 《Engineering in Life Science》1995,15(1):97-106
The 5C outer membrane protein, one of the N. meningitidis class 5 proteins, was preferably expressed in bacteria isolated from the nasopharynx and its role in adhering to the mucosal cells and invading them as well as the development of anti-5C antibodies in healthy carriers was demonstrated. Anti-5C monoclonal antibodies are bactericidal in the presence of the human complement. The immunodominant region of the 5C protein is highly conserved among the different strains of N. meningitidis, and the opc gene, which encodes the protein, does not seem to show antigenic variations. Here the isolation of the opc gene from the Cuban strain B:4:P1.15 by PCR (Polymerase Chain Reaction) is presented. Under the regulation of the tryptophan promoter, the gene was cloned and sequenced in E. coli with a high level of expression and fused to the amino-terminal end of the interleukin-2 gene. In the dot-blot experiments, the presence of the gene in those strains which did not express the protein in the whole cell ELISA was also detectable. 相似文献
144.
Akira Akabayashi C.T.B.V. Zaia James I. Koenig Steven M. Gabriel Ivan Silva Sarah F. Leibowitz 《Peptides》1994,15(8):1437-1444
The peptide galanin (GAL), when injected into the rat hypothalamus, is known to stimulate feeding behavior and affect the secretion of various hormones, including insulin and the adrenal steroid, corticosterone. To determine whether endogenous peptide levels shift in relation to natural rhythms of feeding and circulating hormone levels, rats were sacrificed at different times of the light/dark cycle, and their GAL levels were measured, via radioimmunoassay, in medial hypothalamic dissections and micropunched hypothalamic areas. The results suggest the existence of two distinct diurnal rhythms for hypothalamic GAL. One rhythm, detected exclusively in the area of the SCN, is characterized by bimodal peaks of GAL, threefold higher than basal peptide levels, around the onset of the dark and light periods. The second rhythm shows a single peak of GAL towards the middle of the nocturnal feeding cycle, specifically between the third and sixth hour. This latter rhythm is evident in the dorsal region of the medial hypothalamus, localized specifically to the lateral portion of the PVN. Moreover, it is inversely related to circulating insulin but unrelated to the adrenal steroids, suggesting a possible association between this pancreatic hormone and GAL in the PVN. 相似文献
145.
Colonies of the ponerine antPachycondyla tridentata from Malaysia occur with and without queens. In a total of 7 colonies we found more than 80% of the workers to be mated,
irrespective of the presence or absence of queens. This is a hitherto unknown social organisation in ants. Queens and workers
competed equally for reproduction. In the colonies investigated several ants were laying eggs. Behavioral observations revealed
persistent dominance interactions between colony members. A few ants, but not necessarily a queen, occupied top positions.
Removal of the most dominant ants led to a new hierarchy in which subordinate ants with developed ovaries were attacked significantly
more frequently than non-reproductive ants. On the average, callows were more aggressive than older subordinate ants, displacing
most of the older laying workers in one colony. Nestmate recognition tests revealed that non-reproductive ants were much more
aggressive towards foreign ants than were ants with developed ovaries. 相似文献
146.
Françoise Mead Catherine Habersetzer Danielle Gabouriaut Jacques Gervet 《Journal of Ethology》1994,12(1):43-51
This study focused on how a decrease in prey availability affected the development of aP. dominulus Christ colony. Nutritional oophagy and larval development were parameters found to be most directly affected. The more indirect
effects on the growth of the nest and on offspring production were also analyzed. 相似文献
147.
Prof. Danielle Swinne 《Mycopathologia》1994,128(2):65-65
Editor's Note. Dr Vanbreuseghem was a member of the Mycopathologia Educational Board from 1959 to 1960. 相似文献
148.
Theresa A. Grebe William K. Seltzer Jean DeMarchi Dinithi K. Silva W. W. Doane David Gozal S. F. Richter C. Michael Bowman R. A. Norman Susan N. Rhodes Lucy S. Hernried Shirley Murphy Ivan R. Harwood Frank J. Accurso Karen D. Jain 《American journal of human genetics》1994,54(3):443-446
We have performed molecular genetic analyses of Hispanic individuals with cystic fibrosis (CF) in the southwestern United States. Of 129 CF chromosomes analyzed, only 46% (59/129) carry ΔF508. The G542X mutation was found on 5% (7/129) of CF chromosomes. The 3849+10kbC→T mutation, detected primarily in Ashkenazi Jews, was present on 2% (3/129). R1162X and R334W, mutations identified in Spain and Italy, each occurred on 1.6% (2/129) of CF chromosomes. W1282X and R553X were each detected once. G551D and N1303K were not found. Overall, screening for 22 or more mutations resulted in detection of only 58% of CF transmembrane conductance regulator gene mutations among Hispanic individuals. Analysis of KM19/XV2c haplotypes revealed an unusual distribution. Although the majority of ΔF508 mutations are on chromosomes of B haplotypes, the other CF mutations are on A and C haplotypes at higher-than-expected frequencies. These genetic analyses demonstrate significant differences between Hispanic individuals with CF and those of the general North American population. Assessment of carrier/affected risk in Hispanic CF individuals cannot, therefore, be based on the mutation frequencies found through studies of the general population but must be adjusted to better reflect the genetic makeup of this ethnic group. Further studies are necessary to identify the causative mutation(s) in this population and to better delineate genotype/phenotype correlations. These will enable counselors to provide more accurate genetic counseling. 相似文献
149.
dos Santos Silva Edinaldo N. Kakkassery Francy K. Maas Sibylle Dumont Henri J. 《Hydrobiologia》1994,288(2):119-128
Calanoid copepods, belonging to the new genus and species Keraladiaptomus rangareddyi, were collected from temporary ponds in Kerala State, India. The new genus belongs to the family Diaptomidae, subfamily Diaptominae. It is described in detail and its affinity to the related genera, Arctodiaptomus Kiefer, 1932 and Eodiaptomus Kiefer, 1932, discussed. 相似文献
150.
Enzymes of glucose and methanol metabolism in the actinomycete Amycolatopsis methanolica. 总被引:5,自引:2,他引:3
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A M Alves G J Euverink H J Hektor G I Hessels J van der Vlag J W Vrijbloed D Hondmann J Visser L Dijkhuizen 《Journal of bacteriology》1994,176(22):6827-6835
The actinomycete Amycolatopsis methanolica was found to employ the normal bacterial set of glycolytic and pentose phosphate pathway enzymes, except for the presence of a PPi-dependent phosphofructokinase (PPi-PFK) and a 3-phosphoglycerate mutase that is stimulated by 2,3-bisphosphoglycerate. Screening of a number of actinomycetes revealed PPi-PFK activity only in members of the family Pseudonocardiaceae. The A. methanolica PPi-PFK and 3-phosphoglycerate mutase enzymes were purified to homogeneity. PPi-PFK appeared to be insensitive to the typical effectors of ATP-dependent PFK enzymes. Nevertheless, strong N-terminal amino acid sequence homology was found with ATP-PFK enzymes from other bacteria. The A. methanolica pyruvate kinase was purified over 250-fold and characterized as an allosteric enzyme, sensitive to inhibition by P(i) and ATP but stimulated by AMP. By using mutants, evidence was obtained for the presence of transketolase isoenzymes functioning in the pentose phosphate pathway and ribulose monophosphate cycle during growth on glucose and methanol, respectively. 相似文献