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21.
The addition of 0.167 to 4.0 mM cAMP to gel-filtered rabbit reticulocyte lysates stimulates the initial rate and the extent of polypeptide synthesis. The stimulation is at the initiation step of polypeptide synthesis as measured by the (i) increased dipeptide, methionyl-valine, accumulation in the presence of the specific initiation inhibitor, pactamycin, and (ii) increased formation of the 40 S and 80 S initiation complex when gel-filtered lysates are incubated with [35S]Met-tRNAFMet. Furthermore, a synergistic stimulation of protein synthesis is observed when cAMP and hexose phosphates (which alone elicit a 1.8-fold stimulation of protein synthesis) are added simultaneously to gel-filtered rabbit reticulocyte lysates. These results indicate that cAMP and hexose phosphates are both essential to maintain the high rate of initiation. 相似文献
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We analyze a disturbed form of the general Lotka-Volterra model of an ecosystem with m interacting species. The disturbances act on the intrinsic growth rates of the species and are assumed to be bounded but otherwise unknown. We employ a Lyapunov technique and the concept of "reachable set" from control theory to estimate the set of all possible population densities that are attainable as a result of the disturbances. To calculate estimates for this reachable set, a number of numerical methods that entail the solution to one or more global optimization problems are developed. Specific examples involving two, three, and four species are solved. We also derive an explicit analytical expression that represents an estimate for the reachable set in the m-dimensional case. The estimate is conservative but can be evaluated without carrying out any optimization procedure. We show that methods developed in this paper can be applied to certain other types of nonlinear ecosystem models. 相似文献
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Immunocytochemical Localization of Mandelonitrile Lyase in Mature Black Cherry (Prunus serotina Ehrh.) Seeds 总被引:4,自引:4,他引:0
Mandelonitrile lyase (MDL, EC 4.1.2.10), which catalyzes the reversible dissociation of (R)-(+)-mandelonitrile to benzaldehyde and hydrogen cyanide, was purified to apparent homogeneity from mature black cherry (Prunus serotina Ehrh.) seeds by conventional protein purification techniques. This flavoprotein is monomeric with a subunit molecular mass of 57 kilodaltons. Glycoprotein character was shown by its binding to the affinity matrix concanavalin A-Sepharose 4B with subsequent elution by α-methyl-d-glucoside. Upon chemical deglycosylation by trifluoromethanesulfonic acid, the molecular mass was reduced to 50.9 kilodaltons. Two-dimensional gel analysis of deglycosylated MDL revealed the presence of several subunit isoforms of similar molecular mass but differing slightly in isoelectric point. Polyclonal antibodies were raised in New Zealand white rabbits against deglycosylated and untreated MDL. Antibody titers were determined by enzyme linked immunosorbent and dot immunobinding assays, while their specificities were assessed by Western immunoblot analysis. Antibodies raised against untreated lyase recognized several proteins in addition to MDL. In contrast, antisera raised against deglycosylated MDL were monospecific and were utilized for developmental and immunocytochemical localization studies. SDS-PAGE and immunoblotting analysis of seed proteins during fruit maturation showed that MDL first appeared in seeds shortly after cotyledons began development. In cotyledon cells of mature seeds, MDL was localized primarily in the cell wall with lesser amounts in the protein bodies, whereas in endosperm cells, this labeling pattern was reversed. N-terminal sequence data was gathered for future molecular approaches to the question of MDL microheterogeneity. 相似文献
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In this study four asymptotically equivalent estimates of kinship are derived, in the general case and for kinship between multiallelic loci. Two estimates based on chi 2 agree closely, with the Shannon estimate giving the smaller variance. The PAH, GH, GM, and HBB systems conform to a recombinational model with an evolutionary size of approximately 4,000 and a ratio of recombination to physical distance of approximately 1.4 X 10(-5) morgans/kb, as predicted on the basis of the genetic and physical lengths of the human genome. The INS and D11S12 systems have a much more rapid decline of kinship with physical distance, suggesting overlapping RFLPs (unrecognized allelism), recombinational hot spots, or selection. Sources of error in predicting kinship over small distances are discussed. 相似文献
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We have developed a system for targeting foreign DNA to hepatocytes in vitro using a soluble DNA carrier that takes advantage of receptor-mediated endocytosis to achieve internalization. The idea is based on the fact that hepatocytes possess a unique receptor that binds and internalizes galactose-terminal (asialo)glycoproteins. To create a targetable carrier system that could bind DNA in a nondeforming manner, we used poly(L-lysine) to bind DNA in a strong but noncovalent interaction. An asialoglycoprotein, asialoorosomucoid (AsOR), was chemically coupled to poly(L-lysine) to form an asialoorosomucoid-poly(L-lysine) conjugate. Various proportions of conjugate to DNA were tested to determine conditions that maximized DNA content in a soluble complex and that limited solubility of complexes. To test the targetable gene delivery system, AsOR-poly(L-lysine) conjugate was complexed to the plasmid pSV2 CAT containing the gene for chloramphenicol acetyltransferase (CAT) driven by an SV-40 promoter. We tested this complex using a model system consisting of human hepatoma cell line Hep G2 [asialoglycoprotein receptor (+)], hepatoma SK-Hep 1, IMR-90 fibroblasts, and uterine smooth muscle [receptor (-)] cells. Each cell line was incubated with 0.2 micron filtered AsOR-poly(L-lysine)-DNA complex or controls consisting of DNA plus AsOR, DNA plus poly(L-lysine), or DNA alone. Cells were assayed for the presence of CAT activity as a measure of gene transformation. SK-Hep 1, IMR-90, and smooth muscle [receptor (-)] cells produced no detectable acetylated chloramphenicol derivatives under any of these conditions.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献