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Data are presented regarding the establishment of the pH (designated pH*) of a standard buffer solution suitable as a pH reference in 50 mass% glycerol/water mixtures at temperatures ranging from -20 to 25 degrees C. The buffer material selected was the ampholyte Mops [(3-N-morpholino)-propane sulfonic acid], and the reference standard consists of equal molal amounts of Mops and its sodium salt. The assignment of pH* values is based on measurements of the electromotive force (emf) of cells without liquid junction of the type: Pt;H2(g, 1 atm) / Mops, Na Mopsate, NaCl / AgCl;Ag and the pH* was derived from a determination of K2, the equilibrium constant for the dissociation process (Mops) +/- in equilibrium with (Mopsate)- + H+. The standard emf of the silver-silver chloride electrode in 30, 40, and 50 mass% glycerol/water mixtures was determined from emf measurements of the cell at subzero temperatures with HCl solutions replacing the buffer-chloride mixtures. 相似文献
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Phaeoannellomyces McGinnis et Schell gen. nov., which is based upon P. elegans McGinnis et Schell sp. nov., is proposed for dematiaceous yeasts which produce percurrently proliferating conidiogenous cells. Cladosporium werneckii Horta is transferred to Phaeoannellomyces as P. werneckii (Horta) McGinnis et Schell comb. nov. because the most stable and distinctive synanamorph produced by this fungus consists of annellidic yeast cells. The Phaeococcomycetaceae McGinnis et Schell fam. nov. is proposed in the class Blastomycetes, division Fungi Imperfecti for the dematiaceous yeast genera Phaeoannellomyces and Phaeococcomyces de Hoog. 相似文献
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Regulation of Synthesis of the Aminoacyl-Transfer Ribonucleic Acid Synthetases for the Branched-Chain Amino Acids of Escherichia coli 总被引:10,自引:10,他引:0 下载免费PDF全文
The regulation of synthesis of valyl-, leucyl-, and isoleucyl-transfer ribonucleic acid (tRNA) synthetases was examined in strains of Escherichia coli and Salmonella typhimurium. When valine and isoleucine were limiting growth, the rate of formation of valyl-tRNA synthetase was derepressed about sixfold; addition of these amino acids caused repression of synthesis of this enzyme. The rate of synthesis of the isoleucyl- and leucyl-tRNA synthetases was derepressed only during growth restriction by the cognate amino acid. Restoration of the respective amino acid to these derepressed cultures caused repression of synthesis of the aminoacyl-tRNA synthetase, despite the resumption of the wild-type growth rate. 相似文献
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Catabolite inhibition: a general phenomenon in the control of carbohydrate utilization 总被引:21,自引:9,他引:12 下载免费PDF全文
When Escherichia coli is grown in synthetic medium with radioactive galactose or lactose as the carbon source, the addition of glucose rapidly inhibited utilization of the radioactive substrate, whether the formation of (14)CO(2) or acid-insoluble products was measured. The inhibition was reversed after the removal of glucose. Experiments with mutants blocked in subsequent steps of galactose and lactose metabolism demonstrated that the inhibition occurs prior to the formation of the first metabolic product. The utilization of a variety of sugars, including maltose, lactose, mannose, galactose, l-arabinose, xylose, and glycerol was inhibited by glucose. Of a number of carbohydrates tested as potential inhibitors, only glucose and, to a lesser extent, glucose-6-phosphate (G-6-P) were capable of inhibiting the utilization of all of the substrates. Glucose did not inhibit G-6-P utilization but G-6-P inhibited glucose utilization. With all substrates, except glycerol, there was a delay before the onset of inhibition by G-6-P. We conclude that E. coli has a general regulatory mechanism, termed catabolite inhibition, which controls the activity of early reactions in carbohydrate metabolism, allowing certain substrates to be utilized preferentially. 相似文献
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Molecular cloning and chromosome mapping of a mouse DNA sequence homologous to homeotic genes of Drosophila 总被引:42,自引:0,他引:42
Some of the homeotic genes of Drosophila, involved in the control of segmental development, form a diverged multigene family. A conserved DNA sequence common to these genes has been used to isolate a clone (Mo-10) from the mouse genome which contains a sequence coding for a protein domain that is homologous to the domain conserved in the Drosophila homeotic genes. By structural analogy, this sequence may be involved in the control of metameric pattern formation in the mouse. Mo-10 has been mapped to the proximal portion of mouse chromosome 6, and its position in relationship to genes known to influence mouse morphogenesis is discussed. 相似文献