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Richard E. Kouri Raymond Kiefer Eugene M. Zimmerman 《In vitro cellular & developmental biology. Plant》1974,10(1-2):18-25
Summary Two methods for determining the hydrocarbon-metabolizing enzyme activity of cultured mammalian cells were compared. The method
designed to measure benzo[a]an-thracene-induced aryl hydrocarbon hydroxylase activity could detect and quantify enzyme activities
in low passage rodent cells, but could not reproducibly detect levels in intermediate or high passage mouse, rat, or human
cells. The method designed to measure the ability of a cell to convert benzo[a]pyrene from an organic-soluble to an aqueous
acetone-soluble form proved to be more reproducible. This technique, when modified, was demonstrated to be an effective screening
test for the detection of those lines with higher levels of hydrocarbon-metabolizing enzymes.
Supported by the Council for Tobacco Research and Contract NIH 70-2068 within the Virus Cancer Program, National Cancer Institute,
National Institutes of Health. 相似文献
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Ribosomes, the universal cellular machines, possess spectacular architecture accompanied by inherent mobility, allowing for their smooth performance as polymerases that translate the genetic code into proteins. The site for peptide bond formation is located within a universal internal semi-symmetrical region, which was identified within all contemporary ribosomes. The high conservation of this region implies its existence irrespective of environmental conditions and indicates that it may represent an ancient RNA molecular apparatus. Hence, we named it the “proto-ribosome”. This prebiotic pocket-like RNA entity is suggested to be capable to accommodate substrates whose stereochemistry enables the creation of chemical bonds. It could have evolved from an earlier catalytic RNA entity that we named the “pre-proto-ribosome”, presumed to be a molecular machine capable of performing various essential tasks in the RNA world, which was snatched by the amino acid invaders for producing proteins. 相似文献
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The enzyme dipeptidase-A (DIP-A) in Drosophila melanogaster is coded by a second chromosome locus that is polymorphic for three allozymes in natural populations. DIP-A appears to be the only enzyme in D. melanogaster capable of hydrolyzing the dipeptide glycyl-L-isoleucine, since flies homozygous for null alleles at this locus have no detectable glycyl-L-isoleucine-ase activity. DIP-A activity occurs in many tissues and throughout development, but is particularly high in the larval midgut, suggesting an important role in protein digestion. These observations suggested an experimental design for investigating the adaptive significance of genetic variation in DIP-A activity. Fitness components of DIP-A variants could be estimated and compared under two environmental conditions (defined diets under axenic conditions). In the restrictive environment, the essential amino acid L-isoleucine is provided only in the form of glycyl-L-isoleucine, whereas in the permissive environment, L-isoleucine is provided in free form. We predicted that DIP-A activity would be essential in the restrictive, but not in the permissive environment. The results reported here clearly contradict this prediction. Two stocks homozygous for DIP-A null alleles from different geographic locations are each viable on the restrictive diet. Furthermore, relative viability experiments in which null allele larvae compete with larvae having DIP-A activity provide no evidence for even a partial reduction in egg to adult survival on the restrictive diet. Apparently, the null allele larvae have some alternative mechanism for obtaining L-isoleucine from the dipeptide, even though no glycyl-L-isoleucine-ase activity can be detected in vitro. These results, along with the viability of null alleles for many other enzymes, support the idea that eukaryotes have an intricate network of alternative biochemical pathways through which the same necessary function may be achieved. Such "buffering capacity" makes it very difficult to analyze the effects of enzyme variants on fitness components. 相似文献
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Francesca Fasolo Richard H. Zimmerman Ingrid Fordham 《Plant Cell, Tissue and Organ Culture》1989,16(2):75-87
Leaves taken from micropropagated shoots of several apple (Malus domestica Borkh.) cultivars were cultured in vitro on Linsmaier & Skoog (LS) medium or the rice anther culture medium of Chu et al. (N6) containing various concentrations of either benzyladenine (BA) or thidiazuron (TDZ) plus naphthaleneacetic acid (NAA). Of the TDZ concentrations tested, 10 M was most effective and it was equivalent to, or better than, 22 M BA for both the percentage of leaves regenerating shoots and number of shoots formed per regenerating leaf in almost every experiment. Lower concentrations of NAA (1.1 and 5.4 M) gave best results with both BA and TDZ. N6 medium gave consistently better results than LS. Lowering total salt concentration or total N concentration of LS to that of N6 did not improve the response nor did changing the NO3:NH4 ratio. The 3–4 leaves on the most distal part of the shoot were most responsive and tended to form the most adventitious shoots. Placing the leaf cultures in the dark for the first 2–3 weeks of the culture period produced the best results. Optimum results were obtained by culturing leaves from the distal part of the shoot in the dark for 2 weeks on N6 medium containing 10 M TDZ and 1.1 or 5.4 M NAA, then moving the cultures to 16 h daylight at a photon flux of 60 mol s-1m-2. 相似文献
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Mapping of the structural gene for S-adenosyl homocysteine hydrolase to mouse Chromosome 2, and related sequences to Chromosomes 8 and X 总被引:1,自引:0,他引:1
Alison Pilz Paul Le Tissier Heather Moseley Jo Peters Cathy Abbott 《Mammalian genome》1992,3(11):633-636
Comparative mapping studies in human and mouse have shown that, to date, human Chromosome (Chr) 20 is completely syntenic with distal mouse Chr 2. The structural locus for S-adenosyl-l-homocysteine hydrolase (EC 3.3.1.1) in human, AHCY, maps to 20 qterq13.1, and we report here that the homologous locus in the mouse, Ahcy, maps to distal mouse Chr 2 with gene order Pcna-Ahcy-Ada. Analysis of 123 progeny of an interspecific backcross between a laboratory stock, AN, and Mus spretus using a rat cDNA probe revealed the presence of at least two other Ahcy-related sequences segregating independently in the mouse genome. One, Ahcy-rs1, was mapped to Chr 8 in the BXH recombinant inbred strains, and the other, Ahcy-rs2, shows a pattern of inheritance consistent with X-linkage. 相似文献