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51.
The enhancement of algal growth by organic substrate assimilationis a common laboratory observation, yet few studies have addressedthe interaction of dissolved organic compounds and environmentalfactors for controlling the relative contribution of heterotrophyand autotrophy to the nutrition of these algae. The effectsof light intensity and glycerol addition on the growth, cellvolume, pigmentation, and carbon uptake of the facultative heterotroph,Pyrenomonas salina Santore, were examined. Glycerol additionto cultures growing at a limiting light intensity increasedthe growth rate, increased the average cell volume and cellularstarch content, decreased the cellular phycoerythrin to chlorophyll ratio, and had no effect on the CO2 fixation rate cell1.Glycerol addition to cultures growing at a moderate light intensitythat was saturating for photo-autotrophic growth increased theaverage cell volume and cellular starch content but had no effecton the CO2 fixation rate cell1. The results indicatethat autotrophy was the major process for carbon acquisitionduring the growth of P. salina, but that carbon acquisitionfrom glycerol catabolism also was used to partially supportgrowth of the alga at the limiting light intensity. In addition,glycerol presumably was used to fulfill the energy and/or reductantrequirements of the alga, and to increase the reserve carbohydrate(starch).
1 Current address and address for correspondences: Horn PointEnvironmental Laboratories, University of Maryland, PO Box 775,Cambridge, Maryland 21613, U.S.A. (Received October 29, 1990; Accepted May 31, 1991) 相似文献
52.
Jeanine Brederoo Piet de Wildt Corrie Popp-Snijders Robin F. Irvine Alan Musgrave Herman van den Ende 《Planta》1991,184(2):175-181
InChlamydomonas eugametos gametes, phosphatidylinositol 4-phosphate (PtdInsP) and phosphatidylinositol 4,5-bisphosphate (PtdInsP2) comprised 0.4 and 0.3% of the whole-cell phospholipids. They were concentrated in the plasma membrane around the cell body and were present in low concentrations in the flagellar membrane. When gametes were fed32PO
4
-
, the label was rapidly incorporated into PtdInsP and PtdInsP2 and only slowly incorporated into structural lipids such as phosphatidylethanolamine and phosphatidylglycerol. Similarly, when a pulse of32PO
4
-
was chased with PO
4
-
, the label was rapidly lost from the polyphosphoinositol lipids but not from the structural lipids. The major fatty acids in the polyphosphoinositides were C-22 carbon polyenoic acids (70%). The significance of these results in relationship to intracellular signalling via inositol phosphates and Ca2+ is discussed.Abbreviations InsP3
inositol 1,4,5-trisphosphate
- mt–/mt+
mating-type plus or minus
- PtdA
phosphatidic acid
- PtdEtn
phosphatidylethanolamine
- PtdGro
phosphatidylglycerol
- PtdIns
phosphatidylinositol
- PtdInsP
phosphatidylinositol 4-phosphate;
- PtdInsP2
phosphatidylinositol 4,5-bisphosphate
- TCA
trichloroacetic acid
We thank Frank Schuring for Fig. 5A and Susan Kenter, Hans Kruisselbrink, Saskia Bijvank and Nelleke Corbett for their enthousiastic assistance. 相似文献
53.
Summary We describe a simple method for determining the overall fold of a polypeptide chain from NOE-derived distance restraints. The method uses a reduced representation consisting of two particles per residue, and a force field containing pseudo-bond and pseudo-angle terms, an electrostatic term, but no van der Waals or hard shell repulsive terms. The method is fast and robust, requiring relatively few distance restraints to approximate the correct fold, and the correct mirror image is readily determined. The method is easily implemented using commercially available molecular modeling software. 相似文献
54.
55.
John H. Livesey Alan Carne Clifford H. G. Irvine Jane Ellis Margaret J. Evans Roger Smith Richard A. Donald 《Peptides》1991,12(6):1437-1440
A 41 amino acid peptide, probably identical in structure to human corticotropin releasing factor, was isolated from 70 equine hypothalami by methanol extraction, immunoaffinity chromatography and single step of reverse phase HPLC. The amino acid sequence was determined by gas phase sequence analysis. Probable carboxyl terminal amidation was demonstrated by similar retention times for equine and human corticotropin releasing factor on reverse phase HPLC at pH 8. The likely structure of equine corticotropin releasing factor is: Ser-Glu-Glu-Pro-Pro- Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val-Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn- Arg-Lys-Leu-Met-Glu-Ile-Ile-NH2. The purified peptide is equipotent with human corticotropin releasing factor in an in vitro bioassay and in a human plasma binding protein assay. 相似文献
56.
Crosses among Homokaryons from Commercial and Wild-Collected Strains of the Mushroom Agaricus brunnescens (= A. bisporus) 总被引:9,自引:5,他引:4 下载免费PDF全文
A new technique for the production of hybrid strains of the cultivated mushroom Agaricus brunnescens is described. Homokaryons were recovered from regenerated protoplasts obtained from several heterokaryotic strains. A total of 16 novel hybrids were produced in 63 attempted crosses between paired homokaryons. Recovery of both homokaryons and hybrids was verified by analysis of restriction fragment length polymorphisms. Three of four hybrids fruited in small-scale tests, further confirming that the isolates were true hybrids. Colony morphology alone was found to be a poor indicator of hybrid status. In two instances, three homokaryons crossed successfully in all combinations, suggesting that there are at least three alleles at the putative mating-type locus. Crosses between homokaryons from commercial and wild-collected isolates indicated that these strains belong to the same biological species. 相似文献
57.
Tilapia aurea muscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5-week period. Incomplete compensation is evident in 5-week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress in T. aurea , while plasma glucose and cortisol are sensitive to both acute and chronic temperature stress. 相似文献
58.
Properties of 2-hydroxylaminoimidazoles and their implications for the biological effects of 2-nitroimidazoles 总被引:1,自引:0,他引:1
In aqueous solution, in the presence of ammonium chloride, N1-substituted 2-nitroimidazoles are readily reduced to the corresponding hydroxylamines. In air, under neutral conditions, analogous to the reactions of aromatic hydroxylamines, 2-hydroxylaminoimidazoles are converted to the azoxy derivatives via a base-catalyzed condensation reaction between the hydroxylamine and its oxidation product, the nitroso derivative. In nitrogen, rearrangement to form the 2-amino-4(5)hydroxyimidazole derivative followed by addition of water across the C4-C5 double bond to yield isomers of a 4,5-dihydro-4,5-dihydroxy derivative appears to be a major reaction. 2-hydroxylaminoimidazoles undergo a complex series of reactions with glutathione. The initial reaction is the formation of a labile conjugate involving an N-S-linkage. Subsequently in the presence of excess GSH, under neutral conditions, two stable conjugates identified as 2-amino-4-S-glutathionyl- and 2-amino-5-S-glutathionyl imidazoles are formed. Nucleophilic attack by GSH on the imidazole ring of a nitrenium ion is postulated as the initial step in the formation of the stable GSH conjugates as well as the 2-amino-4,5-dihydro dihydroxy derivative. The results provide a molecular mechanism for many of the biological effects of N1-substituted 2-nitroimidazoles in hypoxic mammalian cells. 相似文献
59.
60.
Induction of functional Fc receptors in P388 leukemia cells : Requirement for multiple differentiation signals 总被引:1,自引:0,他引:1
The development of functional Fc receptors (FcR) during induced differentiation with the tumor promoter, phorbol myristate acetate (PMA), was studied in the murine tumor cell line, P388. PMA induced the appearance of FcR on the membranes of P388 cells as indicated by the binding of IgG-coated sheep red blood cells (IgG-SRBC). Concentrations of PMA as low as 1 ng/ml were sufficient to induce the expression of FcR as well as to inhibit cellular division and to induce adherence in the P388 tumor cell line; however, optimal FcR induction occurred at PMA concentrations of 10-100 ng/ml. Immunofluorescent analysis with heat-aggregated myeloma proteins indicated that PMA induced FcR which were capable of binding IgG2a and IgG2b immunoglobulins, but not IgG1. Adherence to a substratum was determined to be a second required signal for expression of FcR, since PMA induction of P388 tumor cells in teflon dishes failed to fully develop FcR and adherence of P388 cells to poly-L-lysine-coated culture dishes in the absence of PMA was insufficient for FcR expression. FcR which appeared after PMA induction were non-functional in the sense that membrane-bound IgG-SRBC were not ingested to any significant extent by the tumor cells. However, if FcR induction occurred in the presence conA-induced rat spleen cell culture supernatants, phagocytosis of membrane-bound erythrocytes occurred. These findings suggest that for the expression of FcR which are capable of particle internalization, at least three identifiable membrane-transmitted signals are required during differentiation. 相似文献