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871.
872.
We report the first purification and characterization of a eukaryotic algal phosphoglycerate kinase (PGK), Two forms of PGK (PGK1 and PGK2) from the green alga Selenastrum minutum (Naeg.) Collins were purified to electrophoretic homogeneity with specific activities of 1100 and 1069 units · mg?1 protein, respectively. The portion of PGK1 and PGK2 (probably the cytosolic and chloroplastic forms, respectively) in this organism was estimated as 32 and 68%, respectively. PGK1 was more heat-stable than PGK2. The Mr estimation for PGK1 and PGK2 by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and gel filtration indicated that they both were monomeric with a similar Mr of approximately 44 kDa. Antibodies raised against S. minutum PGK1 cross-reacted with PGK2 as well as PGKs from prokaryotic and eukaryotic sources, suggesting that PGK1 was structurally and immunologically closely related to PGK2 and other PGKs, which was consistent with NH2-terminal sequence analysis. Comparative kinetic and regulatory properties of PGK1 and PGK2 from S. minutum were investigated, Both forms exhibited hyperbolic kinetics with respect to both 3-phosphoglycerate (3-PGA) and Mg-adenosine triphosphate2- (MgATP2-) under the conditions tested and had similar Km values for each substrate (PGK1; Km (MgATP2-) = 0.37 mM, Km(3-PGA) = 0.59 mM; PGK2; Km(MgATP2-) = 0.32 mM, Km(3-PGA) = 0.46 mM). PGK1 and PGK2, however, differed significantly in several other kinetic properties. PGK2 had a broad pH optimum between 7.3 and 7.8, as compared to PGK1, with a pH optimum of 7.3 Mg2+ was the most efficient cofactor for both forms; it inhibited PGK1 but not PGK2 at higher concentrations (>10 mM). Other divalent cations (Mn2+, Zn2+, Co2+, Cd2+, and Ca2+) only partially replaced Mg2+ and were more effective for PGK1 than for PGK2, A wide range of metabolites was examined for regulatory properties. Energy charge was the most important factor in regulating the two forms of S. minutum PGK. These results were interpreted in light of the regulation of this kinase in response to the cell energy requirement and the need for glycolytic carbon flow to provide carbon skeletons for amino acid biosynthesis. 相似文献
873.
Dorothy E. Croall 《Biochimica et Biophysica Acta (BBA)/General Subjects》1982,714(2):200-208
The interactions in vitro between [3H]estradiol and liver proteins from Xenopus laevis have been examined to determine if the binding reaction meets criteria of steroid-receptors which may function in the induction of vitellogenesis. Estrogenic hormones associated with proteins in serum and liver cytosol from Xenopus laevis. However, the interactions between soluble liver proteins and estrogens apparently do not result from serum contamination of liver as specific binding was distinguishable by ligand affinity and by differential mobility on polyacrylamide gels. Steroid ligands bound by liver proteins during incubation in vitro were examined by solubility and by thin-layer chromatography. Only a small percentage (13%) of the bound radioactive ligand was recovered as the original tritium-labeled steroid, 17β-estradiol. The major ligand was recovered as a water-soluble metabolite of estradiol which was identified tentatively as an estradiol-glucoside. To investigate whether the protein-bound estradiol metabolite(s) merely masks a small amount of authentic estradiol-receptor complexes or if the metabolite could be an intermediate in estrogen function, isolated liver nuclei were incubated with liver cytosol containing 3H-labeled steroid-protein complexes or with serum protein-bound [3H]estradiol. Nuclei preferentially accumulated 3H-labelea steroids from liver cytosol protein-steroid complexes relative to [3H]estradiol from serum proteins. However, analysis of the steroids recovered in the nuclei after incubation with liver cytosol revealed that both 17β-[3H]estradiol and the 3H-labeled water-soluble metabolite were retained in vitro by nuclei. 相似文献
874.
Thigmomorphogenesis: The relationship of mechanical perturbation to elicitor-like activity and ethylene production 总被引:2,自引:0,他引:2
An extracellular solution obtained from bean ( Phaseolus vulgaris L. cv. Resistant Cherokee Wax) stems induced phytoalexin-like substance and ethylene production in a soybean [ Glycine max (L.) Merr. cv. Wayne] cotyledon bioassay. The elicitor-like activity for phytoalexin formation and ethylene production was increased by mechanical perturbation of bean stems. Moreover, the application of extracted or known elicitors to bean plants mimicked the effect of mechanical perturbation (i.e., inhibition of stem elongation and enhancement of radial growth). The effects of extract when applied exogenously, on elicitor-like activity in the bioassay as well as stem thickening were decreased by aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis. These results suggest that elicitor-like substances which are formed in response to mechanical perturbation contribute to the thigmomorphogenesis. 相似文献
875.
Substance P is rapidly converted by enzyme(s) in human plasma to des-[Arg1Pro2]-substance P (fragment 3-11) and to des-[Arg1Pro2Lys3Pro4]-substance P (fragment 5-11). These metabolites were isolated by HPLC and partially sequenced. No evidence was obtained for deamidation of substance P in plasma or for the formation of the N-terminal tetrapeptide [Arg-Pro-Lys-Pro]. The data suggest that substance P is metabolized in human plasma by an enzyme with the specificity of dipeptidyl-aminopeptidase IV. Consistent with this hypothesis, the rate of degradation of substance P measured with an antibody directed against the N-terminal region is 2-3-fold greater than measured with a C-terminally directed antibody. The degrading activity of plasma was purified 522-fold and was eluted from a gel filtration column in the molecular weight zone 150 000-170 000 and from a chromatofocusing column in the pH range 4.5 to 5.5. 相似文献
876.
A new anthraquinone metabolite, versicolorone, has been isolated from Aspergillus versicolor. 相似文献
877.
Kelly C. Detmann Wagner L. Araújo Samuel C.V. Martins Alisdair R. Fernie Fábio M. DaMatta 《Plant signaling & behavior》2013,8(1)
Although the beneficial role of silicon (Si) in stimulating the growth and development of many plants is generally accepted, our knowledge concerning the physiological and molecular mechanisms underlying this response remains far from comprehensive. Considerable effort has been invested in understanding the role of Si on plant disease, which has led to several new and compelling hypotheses; in unstressed plants, however, Si is believed to have no molecular or metabolic effects. Recently, we have demonstrated that Si nutrition can modulate the carbon/nitrogen balance in unstressed rice plants. Our findings point to an important role of Si as a signaling metabolite able to promote amino acid remobilization. In this article we additionally discuss the agronomic significance of these novel observations and suggest Si nutrition as an important target in future attempts to improve yields of agronomic crops. 相似文献
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