The reactions of aliphatic and aromatic amines with reducing sugars are important in both drug stability and synthesis. The
formation of glycosylamines in solution, the first step in the Maillard reaction, does not typically cause browning but results
in decreased potency and is hence significant from the aspect of drug instability. The purpose of this research was to present
(1) unreported ionic equilibria of model reactant (kynurenine), (2) the analytical methods used to characterize and measure
reaction products, (3) the kinetic scheme used to measure reaction rates and (4) relevant properties of various reducing sugars
that impact the reaction rate in solution. The methods used to identify the reversible formation of two products from the
reaction of kynurenine and monosaccharides included LC mass spectrometry, UV spectroscopy, and 1-D and 2-D 1H–1H COSY NMR spectroscopy. Kinetics was studied using a stability-indicating HPLC method. The results indicated the formation
of α and β glycosylamines by a pseudo first-order reversible reaction scheme in the pH range of 1–6. The forward reaction
was a function of initial glucose concentration but not the reverse reaction. It was concluded that the reaction kinetics
and equilibrium concentrations of the glycosylamines were pH-dependent and also a function of the acyclic content of the reacting
glucose isomer. 相似文献
Method for production and regeneration of Lactobacillus delbrueckii protoplasts are described. The protoplasts were obtained by treatment with a mixture of lysozyme and mutanolysin in protoplast
buffer at pH 6.5 with different osmotic stabilizers. The protoplasts were regenerated on deMan, Rogosa and Sharpe (MRS) with
various osmotic stabilizers. Maximum protoplast formation was obtained in protoplast buffer with sucrose as an osmotic stabilizer
using a combination of lysozyme (1 mg/ml) and mutanolysin (10 μg/ml). Maximum protoplast regeneration was obtained on MRS
medium with sucrose (0.5 M) as an osmotic stabilizer. The regeneration medium was also applicable to other species of lactobacilli
as well. This is, to our knowledge, the first report on protoplast formation and efficient regeneration in case of L. delbrueckii. 相似文献
Human erythrocytes become agglutinable with concanavalin A (Con A) after treatment with various proteinases or neuraminidase. The extent of agglutinability achieved with different enzymes is, however, different: Pronase, papain, trypsin, neuraminidase and chymotrypsin enhance the agglutinability in decreasing order, the last being barely effective. The actions of the enzymes on band 3, the Con A receptor, do not correlate with their abilities to increase the agglutinability: Pronase, papain and chymotrypsin cleave the protein, but not trypsin or neuraminidase. No significant differences are found in the number of Con A-binding sites or the affinities for the lectin between the normal and trypsin- or Pronase-treated cells. Thus the receptor does not seem to play a role in determining the Con A-agglutinability of erythrocytes. On the other hand, the cleavage of glycophorins, especially glycophorin A, and the release of sialic acid (in the peptide-bound form) are well-correlated with the enhancement in agglutination after the action of proteinases. The release of sialic acid by graded neuraminidase digestion and the increase in Con A-agglutinability show a correlation coefficient of 0.88. The major inhibitory role of glycophorin A in the process is indicated by the agglutination of En(a) heterozygous erythrocytes; the cells, known to bear about 50% glycophorin A molecules in their membrane, are agglutinated approximately half as well without proteolysis as are the trypsin-treated cells. Possible mechanisms by which glycophorin A could affect Con A-mediated agglutination are discussed. 相似文献
In the erythrocyte membrane, the mobility of band 3 protein, the receptor for concanavalin A (Con A), is drastically reduced by the membrane skeleton. Yet, the vesicles free of membrane skeletal proteins, isolated from the highly agglutinable proteinase-treated cells, are found to be devoid of Con A agglutinability. The vesicles bind Con A in normal amounts, and remain agglutinable with the wheat germ and Ricinus agglutinins. Intracellular entrapment of monospecific antibodies to spectrin and 4.1 protein (two of the major skeletal components of the membrane) is also found to inhibit agglutination by 30-50%. Thus the membrane skeleton appears to play a positive role in the agglutination of the cells with Con A. The anti-ankyrin antibodies are found to be without any effect. The anti-band 3 (cytoplasmic domain) antibodies are also inhibitory to agglutination. Since Con A binding to cells alters the shape responses and deformability of the cells, and the cells resist fragmentation at 49 degrees C, the properties of the whole skeleton, especially spectrin, appear to be changed. The Con A-bound membranes also do not release the complex of spectrin-band 4.1-actin when extracted with a hypotonic medium. It appears that Con A binding leads to interaction of the cytoplasmic domain of the receptor with a skeletal component, possibly spectrin. Subsequent to this, the receptor molecules and the skeletal proteins undergo aggregation in the membrane, which is detected by their crosslinking by an 8.6-A span bifunctional reagent. The contractility believed to be associated with the membrane skeleton may be responsible for the aggregation. 相似文献
Summary
Aspergillusniger NCIM 1207 producing significantly high levels of -glucosidase was found to secrete hemicellulolytic enzymes (xylanase and -xylosidase) in the culture medium. High yields of -xylosidase were obtained when it was grown on either xylan (3%) or wheat bran (4%). Cellulose was a poor inducer of -xylosidase. The pH and temperature optima for-xylosidase were 4.5 and 65°C respectively.NCL Communication No. 3751 相似文献
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
Transbilayer phospholipid distribution, membrane skeleton dissociation/association, and spectrin structure have been analysed in human erythrocytes after subjecting them to heating at 50 degrees C for 15 min. The membrane skeleton dissociation/association was determined by measuring the Tris-induced dissociation of Triton-insoluble membrane skeletons (Triton shells), the spectrin-actin extractability under low ionic conditions, and the binding of spectrin-actin with normal erythrocyte membrane inside-out vesicles (IOVs). The spectrin structure was ascertained by measuring the spectrin dimer-to-tetramer ratio as well as the spectrin tryptophan fluorescence. Both the Tris-induced Triton shell dissociation and the spectrin-actin extractability under low ionic conditions were considerably reduced by the heat treatment. Also, the binding of heated erythrocyte spectrin-actin to IOVs was significantly smaller than that observed with the normal cell spectrin-actin. Further, the quantity of spectrin dimers was appreciably increased in heat-treated erythrocytes as compared to the normal cells. This change in the spectrin dimer-to-tetramer ratio was accompanied by marked changes in the spectrin tryptophan fluorescence. In spite of these heat-induced alterations in structure and bilayer interactions of the membrane skeleton, the inside-outside glycerophospholipid distribution remained virtually unaffected in the heat-treated cells, as judged by employing bee venom and pancreatic phospholipase A2, fluorescamine and Merocyanine 540 as the external membrane probes. These results strongly indicate that membrane bilayer-skeleton interaction is not the major factor in determining the transbilayer phospholipid asymmetry in human erythrocyte membrane. 相似文献
We have explored the possibilities that cell volume is regulated by the status of microtubule assembly and cyclic AMP metabolism and may be coordinated with shape change. Treatment of J774.2 mouse macrophages with colchicine caused rapid microtubule disassembly and was associated with a striking increase (from 15-20 to more than 90 percent) in the proportion of cells with a large protuberance at one pole. This provided a simple experimental system in which shape changes occurred in virtually an entire cell population in suspension. Parallel changes in cell volume could then be quantified by isotope dilution techniques. We found that the shape change caused by colchicine was accompanied by a decrease in cell volume of approximately 20 percent. Nocodozole, but not lumicolchicine, caused identical changes in both cell shape and cell volume. The volume loss was not due to cell lysis nor to inhibition of pinocytosis. The mechanism of volume loss was also examined. Colchicine induced a small but reproducible increase in activity of the ouabain-sensitive Na(+), K(+)-dependent ATPase. However, inhibition of this enzyme/transport system by ouabain did not change cell volume nor did it block the colchicines-induced decrease in volume. One the other hand, SITS (4’acetamido, 4-isothiocyano 2,2’ disulfonic acid stilbene), an inhibitor of anion transport, inhibited the effects of colchicines, thus suggesting a role for an anion transport system in cell volume regulation. Because colchicine is known to activate adenylate cyclase in several systems and because cell shape changes are often induced by hormones that elevate cyclic AMP, we also examined the effects of cyclic AMP on cell volume. Agents that act to increase syclic AMP (cholera toxin, which activates adenylate cyclase; IBMX, and inhibitor of phosphodiesterase; and dibutyryl cyclic AMP) all caused a volume decrease comparable to that of colchicine. To define the effective metabolic pathway, we studied two mutants of J774.2, one deficient in adenylate cyclase and the other exhibiting markedly reduced activity of cyclic AMP-dependent protein kinase. Cholera toxin did not produce a volume change in either mutant. Cyclic AMP produced a decrease in the cyclase-deficient line comparable to that in wild type, but did not cause a volume change in the kinase- deficient line. This analysis established separate roles for cyclic AMP and colchicine. The volume decrease induced by cyclic AMP requires the action of a cyclic AMP-dependent protein kinase. Colchicine, on the other hand, induced a comparable volume change in both mutants and wild type, and thus does not require the kinase. 相似文献
An experiment was performed during the grazing seasons of 1998, 1999 and 2000 to study the influence of the antiparasitic drug ivermectin and the nematophagous fungus Duddingtonia flagrans on cattle dung disintegration. The faeces originated from groups of animals that were part of a separate grazing experiment where different control strategies for nematode parasite infections were investigated. Each group consisted of 10 first-season grazing cattle that were either untreated, treated with the ivermectin sustained-release bolus, or fed chlamydospores of D. flagrans. Faeces were collected monthly on 4 occasions and out of pooled faeces from each group, 4 artificial 1 kg dung pats were prepared and deposited on nylon mesh on an enclosed pasture and protected from birds. The position of the new set of pats was repeated throughout the 3 years of the study. Each year, the dung pats were weighed 4, 6, 8 and 10 weeks after deposition and immediately afterwards replaced to their initial positions.
Results showed that there was no difference in faecal pat disintegration between groups. However, the time-lag between deposition and complete disintegration of the faeces varied significantly between deposition occasions. Dung pats disappeared within 2 weeks (visual observation) when subjected to heavy rainfall early after deposition, whereas an extended dry period coincided with faeces still remaining 12 months after deposition.