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71.
The epithelial lining of the gastrointestinal (GI) tract is in a state of continuous cell renewal, and the proliferating and differentiating/differentiated cell populations are spatially clearly demarcated. Members of the epidermal growth factor (EGF) family of peptides, the trefoil peptides and enteroglucagon appear to be the most important enterotrophic molecules for both normal cell renewal and healing after cell damage. Transforming growth factor-a (TGF-a) appears to be the primary physiological ligand for the EGF receptor (EGFR), promoting normal cell renewal, and TGF-a/EGFR are part of an autocrine loop in many intestinal cancers. In response to damage, a differentiating cell lineage arises from adjacent epithelium secreting EGF, TGF-a and trefoil peptides; this may be viewed as part of a ‘repair kit’ in damaged endodermally-derived tissue. 相似文献
72.
The characteristics of sulphate uptake into right-side-out plasma-membrane vesicles isolated from roots of Brassica napus L., Metzger, cv. Drakkar, and purified by aqueous polymer two-phase partitioning, were investigated. Sulphate uptake into the vesicles was driven by an artificially imposed pH gradient (acid outside), and could be observed for 5–10 min before a plateau was reached and no further net uptake occurred. The uptake was partially inhibited in the presence of depolarizing agents and little uptake was observed in the absence of an imposed pH gradient. Uptake was strongly pH-dependent, being greatest at more acidic pH. After imposition of a pH gradient, the capacity for uptake decreased slowly (t1/2>10 min). The uptake had a high-affinity component which was strongly dependent on the external proton concentration (K m=10μM at pH 5.0, 64 μM at pH 6.5). The K m for protons varied from 0.4–1.9 μM as the sulphate concentration was reduced from 33 to 1 μM. A low-affinity component was observed which could be resolved at low temperatures (0 °C). Microsomal membranes that partitioned into the lower phase of the two-phase system gave no indication of high-affinity sulphate transport. Sulphate uptake into plasma-membrane vesicles isolated from sulphur-starved plant material was approximately twofold greater than that observed in those isolated from sulphate-fed plant material. Isolated vesicles therefore mirror the well-known in-vivo response of roots, indicating an increase in the number of transporters to be, at least in part, the underlying cause of derepression. 相似文献
73.
Adnan M. M. Mjalli Kevin T. Chapman Malcolm MacCoss Nancy A. Thornberry 《Bioorganic & medicinal chemistry letters》1993,3(12):2689-2692
Phenylalkyl ketones are potent reversible inhibitors of interleukin-1β converting enzyme (ICE). The extended alkyl chain ketones AcTyrValAlaAspCO(CH2)nPh display increased potency over the simple aryl ketone. In particular, the tetrapeptide AcTyrValAlaAspCOPh has a Ki of 10μM while AcTyrValAlaAspCO(CH2)5Ph has a Ki of 18.5nM. 相似文献
74.
Lars J. S. Knutsen Jesper Lau Malcolm J. Sheardown Christian Thomsen 《Bioorganic & medicinal chemistry letters》1993,3(12):2661-2666
The synthesis and SAR of a series of novel derivatives of N-aminoadenosine is described, along with their in vitro effects in biochemical assays. The rat brain A1 adenosine receptor binding of these compounds is very dependent upon the purine 2-substituent. The novel agonist, 2-chloro-N-[4-(phenylthio)-1-piperidinyl]adenosine, exhibits a Li value for A1 receptor binding of <1 nM. 相似文献
75.
Malcolm Cämmerer Thomas Mayer Carolin Schott Juliane Steingroewer Ralf Petrich Helko Borsdorf 《Engineering in Life Science》2023,23(4):e2200039
The cultivation of algae either in open raceway ponds or in closed bioreactors could allow the renewable production of biomass for food, pharmaceutical, cosmetic, or chemical industries. Optimal cultivation conditions are however required to ensure that the production of these compounds is both efficient and economical. Therefore, high-frequency analytical measurements are required to allow timely process control and to detect possible disturbances during algae growth. Such analytical methods are only available to a limited extent. Therefore, we introduced a method for monitoring algae release volatile organic compounds (VOCs) in the headspace above a bioreactor in real time. This method is based on ion mobility spectrometry (IMS) in combination with a membrane inlet (MI). The unique feature of IMS is that complete spectra are detected in real time instead of sum signals. These spectral patterns produced in the ion mobility spectrum were evaluated automatically via principal component analysis (PCA). The detected peak patterns are characteristic for the respective algae culture; allow the assignment of the individual growth phases and reflect the influence of experimental parameters. These results allow for the first time a continuous monitoring of the algae cultivation and thus an early detection of possible disturbances in the biotechnological process. 相似文献
76.
Arland T. Hotchkiss Michael R. Gretz Kevin B. Hicks R. Malcolm Brown 《Journal of phycology》1989,25(4):646-654
The two-layered, fibrillar cell wall of Mougeotia C. Agardh sp. consisted of 63.6% non-cellulosic carbohydrates and 13.4% cellulose. The orientation of cellulose microfibrils in the native cell wall agrees with the multinet growth hypothesis, which has been employed to explain the shift in microfibril orientation from transverse (inner wall) toward axial (outer wall). Monosaccharide analysis of isolated cell walls revealed the presence of ten sugars with glucose, xylose and galactose most abundant. Methylation analysis of the acid-modified, 1 N NaOH insoluble residue fraction showed that it was composed almost exclusively of 4-linked glucose, confirming the presence of cellulose. The major hemicellulosic carbohydrate was semi-purified by DEAE Sephacel (Cl?) anion-exchange chromatography of the hot 1 N NaOH soluble fraction. This hemicellulose was a xylan consisting of a 4-xylosyl backbone and 2,4-xylosyl branch points. The major hot water soluble neutral polysaccharide was identified as a 3-linked galactan. Mougeotia cell wall composition is similar to that of (Charophyceae) and has homologies with vascular plant cell walls. Our observations support transtructural evidence which suggests that members of the Charophyceae represent the phylogenetic line that gave rise to vascular plants. Therefore, the primary cell walls of vascular plants many have evolved directly from structures typical of the filamentous green algal cell walls found in the Charophyceae. 相似文献
77.
T-box genes are defined by the presence of a conserved sequence, the so-called T-box; this codes for the T-domain, which is involved in DNA-binding and protein dimerisation. Members of this gene family have been found in all metazoans, from diploblasts to humans, and mutations in T-box gene family members in humans have been linked to several congenital disorders. Sequencing of the complete genomes of a range of invertebrate and vertebrate species has allowed the classification of individual T-box genes into five subfamilies: Brachyury, T-brain1, Tbx1, Tbx2 and Tbx6. This review will largely focus on T-box genes identified in organisms whose genomes have been fully sequenced, emphasising how comparative studies of the T-box gene family will help to reveal the roles of these genes during development and in the adult. 相似文献
78.
Detached leaves of Bryophyllum fedtschenkoi Hamet et Perrier kept in normal air show a single period of net CO2 fixation on transfer to constant darkness at temperatures in the range 0–25 °C. The duration of this initial fixation period is largely independent of temperature in the range 5–20 °C, but lengthens very markedly at temperatures below 4 °C, and is reduced at temperatures above 25 °C. The onset of net fixation of CO2 on transfer of leaves to constant darkness is immediate at low temperatures, but is delayed as the temperature is increased. The ambient temperature also determines whether or not a circadian rhythm of CO2 exchange occurs. The rhythm begins to appear at about 20 °C, is most evident at 30 °C and becomes less distinct at 35 °C. The occurrence of a distinct circadian rhythm in CO2 output at 30° C in the absence of a detectable rhythm in PEPCase kinase activity shows that the kinase rhythm is not a mandatory requirement for the rhythm of PEPCase activity. However, when it occurs, the kinase rhythm undoubtedly amplifies the PEPCase rhythm.Abbreviation PEPCase
phosphoenolpyruvate carboxylase
We thank the Agricultural and Food Research Council for financial support for this work. 相似文献
79.
Anthony G. Lee Kate A. Dalton Richard C. Duggleby J. Malcolm East Anthony P. Starling 《Bioscience reports》1995,15(5):289-298
Effects of lipid structure on the function of the Ca2+-ATPase of skeletal muscle of sarcoplasmic reticulum are reviewed. Binding of phospholipids to the ATPase shows little specificity. Phosphatidylcholines with short (C14) or long (C24) fatty acyl chains have marked effects on the activity of the ATPase, including a change in the stoichiometry of Ca binding. Low ATPase activity in gel phase lipid follows from low rate of phosphorylation. Phosphatidylinositol 4-phosphate increases ATPase activity by increasing the rate of dephosphorylation of the phosphorylated ATPase. Stimulation is not seen with other anionic phospholipids; phosphatidic acid decreases ATPase activity in a Mg2+-dependent manner.Abbreviations di(C141)PC
dimyristoleoylphosphatidycholine
- di(C160)PC
dipalmitoylphosphatidylcholine
- di(C181)PC
dioleoylphosphatidylcholine
- di(Br2C180)PC
dibromostearoylphosphatidylcholine
- di(C241)PC
dinervonylphosphatidylcholine
- di(C181)PA
dioleoylphosphatidic acid
- di(C181)PE
dioleoylphosphatidylethanolamine
- Ptdlns
phosphatidylinositol
- PtdIns-4P
phos-phatidylinositol 4-phosphate 相似文献
80.
Extracellular polysaccharide of Nostoc commune (Cyanobacteria) inhibits fusion of membrane vesicles during desiccation 总被引:6,自引:0,他引:6
Donna R. Hill Thomas W. Keenan Richard F. Helm Malcolm Potts Lois M. Crowe John H. Crowe 《Journal of applied phycology》1997,9(3):237-248
Cells of the cyanobacterium Nostoc commune secrete a complex, high molecular weight, extracellular polysaccharide (EPS) which
accumulates to more than 60% of the dry weight of colonies. The EPS was purified from the clonal isolate N. commune DRH1.
The midpoint of the membrane phase transition (Tm) of desiccated cells of N. commune CHEN was low (Tm
dry = 8 °C) and was comparable to the Tm of rehydrated cells((Tm)H20 = 6 °C). The EPS was not responsible for the depression of Tm. However, the EPS, at low concentrations, inhibited specifically the fusion of phosphatidylcholine membrane vesicles when
they were dried in vitro at0% relative humidity (−400 MPa). Low concentrations of a trehalose:sucrose mixture, in a molar
ratio which corresponded with that present in cells in vivo, together with small amounts of the EPS, were efficient in preventing
leakage of carboxyfloroscein (CF) from membrane vesicles. Freeze-fracture electron microscopy resolved complex changes in
the structure of the EPS and the outer membrane in response to rehydration of desiccated cells. The capacity of the EPS to
prevent membrane fusion, the maintenance of a low Tm
dry in desiccated cells, and the changes in rheological properties of the EPS in response to water availability, constitute what
are likely important mechanisms for desiccation tolerance in this cyanobacterium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献