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1.
Studies on the substrate specificity of cAMP-dependent protein kinase using diastereomeric peptides.
M Eller A Sepp R Toomik P Ekman J J?rv U Ragnarsson L Engstr?m 《Biochemistry international》1991,25(3):453-460
A set of six different diastereomeric hexapeptides RRASVA, each with a D-amino acid residue successively in the six positions, was synthesized and tested as substrates of protein kinase A. It was found that the peptide with D-Ser was neither a substrate, nor an inhibitor of the enzyme. The other five peptides were active as substrates with slightly lower kcat values than that of the all-L amino acid peptide. However, the apparent Km values increased by one to two orders of magnitude, especially when the second arginine or the alanine residue preceding the serine was substituted. The results are discussed. 相似文献
2.
Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO2-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life.Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO2 uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO2 fixation is only performed when the water status of the plant can be improved simultaneously.Abbreviations CAM
Crassulacean acid metabolism
- VPD
water vapour pressure deficit
Dedicated to Professor H. Ziegler on the occasion of his 60th birthday 相似文献
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This paper presents a generalization of the classical compartmental models using the concept of "pipes" between the compartments and taking into account the time needed for the material to pass through these pipes. A general linear delay differential system describing such models is derived and some properties of its solutions-such as nonnegativity, boundedness, stability-are established. For stationary and asymptotically stationary systems the asymptotic solution is obtained, too. The theory presented generalizes several earlier results concerning more special equations. 相似文献
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Abstract: The enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) has been isolated from an acetone powder of human subcortical white matter. The yield was about 11 mg from 28 g of powder and a specific activity of 213 unitdmg protein was obtained using 2',3'-cyclic CMP as the substrate. A major protein band of molecular weight approx. 96,000 was found by gel electrophoresis under nonreducing conditions. However, two distinct protein bands of molecular weight 46,000 ± 1400 and 48,000 ± 1400 were observed when the protein sample was reduced with 10 mM-dithiothreitol and subjected to electrophoresis in more restrictive 12-15% polyacrylamide-SDS gels. This molecular weight is lower than that previously reported for the bovine enzyme. Antibodies against the purified human enzyme have been raised in New Zealand white rabbits. 相似文献
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Song Huijia Jespersen Emil Guo Xiao Du Ning Xie Liujuan Pei Lixin Ye Siyuan Wang Renqing Brix Hans Eller Franziska Guo Weihua 《Hydrobiologia》2021,848(14):3353-3369
Hydrobiologia - Soil salinity diminishes the dominance of species and affects their distribution. Phragmites australis is a dominant ecosystem engineer with broad distribution, high intraspecific... 相似文献
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Xie Liujuan Jespersen Emil Ye Siyuan Pei Lixin Song Huijia Guo Xiao Guo Weihua Brix Hans Eller Franziska 《Hydrobiologia》2021,848(14):3331-3351
Hydrobiologia - Phragmites australis is a cosmopolitan plant species with high intraspecific diversity and phenotypic plasticity. Due to its variability and large ecological niche breadth,... 相似文献
10.
Zoltan Beck Linda L. Jagodzinski Michael A. Eller Doris Thelian Gary R. Matyas Anjali N. Kunz Carl R. Alving 《PloS one》2013,8(11)
Chronic HIV-1 infection is associated with persistent viremia in most patients, but it remains unclear how free virus may survive the potential hostile effects of plasma. We investigated whether sites might exist on the surfaces of circulating blood cells for protection of infectious HIV-1 particles. Red blood cells (RBC) either from blood of uninfected normal individuals, or from blood obtained without EDTA from chronically infected HIV-1 patients, invariably contained a small number of RBC having attached platelets as determined by flow cytometry, light microscopy, and immunofluorescence microscopy. After mixing normal RBC with platelet-rich plasma, discrete populations of RBC, platelets, and complexes of platelets attached to RBC were purified by fluorescence-activated cell sorting. Upon incubation of purified cells or platelets with HIV-1 followed by washing and co-incubation with CD4-positive peripheral blood mononuclear cells (PBMC), platelets, and platelet-RBC complexes, but not platelet-free RBC, caused infection of PBMC. Infection was prevented by pre-treating the platelet-RBC complexes with EDTA. Plasma and RBC (comprising a RBC/platelet-RBC mixture) from chronically infected patients with low viral loads were also co-incubated with PBMC ex vivo to determine the presence of infectious HIV-1. All freshly isolated plasmas from the HIV-1-infected donors, obtained in the absence of anticoagulant, were noninfectious. Interestingly, the RBC from most of the patients caused cell-cell infection of PBMC that was prevented by stripping the RBC with EDTA. A monoclonal antibody to DC-SIGN partially inhibited cell-cell HIV-1 infection of PBMC by normal RBC pre-incubated with platelets and HIV-1. We conclude: (a) platelet-free EDTA-free plasma from chronically infected HIV-1 patients, although containing viral RNA, is an environment that lacks detectable infectious HIV-1; (b) platelets and platelet-RBC complexes, but not purified RBC, bind infectious HIV-1; (c) DC-SIGN, and possibly other C-type lectins, may represent binding sites for infectious HIV-1 on platelets and platelet-RBC complexes. 相似文献