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171.
Pseudomonas sp. MA grows on methylamines as a sole source of carbon, nitrogen, and energy. The transport of methylamine into the organism was investigated. It was found that this organism possesses an inducible transport system for methylamine having the following physical parameters: pH optimum, 7.2; temperature optimum, 30 to 35 degrees C; Km, 1 to 30 mM; Vmax, 90 to 120 nmol/min per mg (dry weight) of cells. Methylamine uptake was curtailed by azide, cyanide, and carbonyl cyanide-m-chlorophenylhydrazone; osmotic shock treatment reduced the uptake by 50%. The uptake was not effectively inhibited by ammonium ion, amino acids, or amides, but was competitively inhibited by short-chain alkylamines. Cells grown on succinate-ammonium chloride did not possess the transport system, but it could be induced in such cells by methylamine in 20 h. Cells grown with methylamine as a sole nitrogen, but not carbon, source transported methylamine at a reduced rate. 相似文献
172.
Purification of soluble guanylate cyclase from rat liver resulted in an apparent loss of enzyme activation by nitric oxide that could be restored by dithiothreitol. methemoglobin, bovine serum albumin, or sucrose. Although hemoglobin also permitted some activation with nitric oxide, the effect of other agents to restore enzyme activation was prevented with hemoglobin. As a result of enzyme purification, there is an alteration of the dose-response relationship for nitric oxide activation. After partial enzyme purification, relatively high concentrations of nitric oxide that were stimulatory in crude enzyme preparations had no effect on enzyme activity. However, partially purified or homogeneous enzyme was activated by lower concentrations of nitric oxide. The bell-shaped dose-response curve for nitric oxide was shifted to the left with guanylate cyclase purification. The addition of dithiothreitol, methemoglobin, bovine serum albumin, or sucrose to enzyme markedly broadens the dose-response curve for nitric oxide. Thus, the apparent loss of responsiveness to nitric oxide with purification is a function of increased sensitivity of guanylate cyclase to nitric oxide. Increased sensitivity to nitric oxide with enzyme purification probably results from the removal of heme, proteins, and small molecules that can serve as scavengers or sinks for nitric oxide and prevent excessive oxidation of the enzyme. 相似文献
173.
Human corpora lutea of defined ages were excised at operation, cut into pieces and incubated in the presence of HCG, PGF2 alpha and PGE2 alone or in combination. Following incubation cAMP formation in tissue and medium was determined. HCG-stimulated tissue cAMP content was most pronounced at a corpus luteum age of 7-10 days after ovulation. This stimulation was antagonized by PGF2 alpha in corpora lutea older than 6 days. PGE2 stimulated cAMP formation per se and this effect was more pronounced when HCG and PGE2 were combined. A possible role for PGF2 alpha as a luteolytic substance in the human is suggested. 相似文献
174.
Conformation of methylated sequences in HeLa cell 18-S ribosomal RNA: nuclease S1 as a probe 总被引:1,自引:0,他引:1
18-S rRNA from HeLa cells was digested with nuclease S1. Under the conditions employed 15% of the total nucleotides and some 50% of the methylated nucleotides were released as low-molecular-weight products. The material which was precipitable by 70% ethanol after nuclease S1 digestion was subjected to further digestion by combined T1 plus pancreatic ribonucleases or by T1 ribonuclease alone, and fingerprints were prepared. It was found that the four sites which are modified late during ribosome maturation, and which contain base modifications, were all accessible to nuclease S1. By contrast fewer than one-half of the sites which are modified early during ribosome maturation, and which contain 2'-O-methyl groups, were accessible to nuclease S1; the remainder were protected, presumably by secondary or tertiary interactions within 18-S rRNA. 相似文献
175.
M. A. Khan 《The Histochemical journal》1978,10(6):641-644
Synopsis The non-enzymatic histochemical technique Haematoxylin-Basic Fuchsinpicric acid (HBFP) was studied in fresh-frozen and Carnoy-fixed, paraffin-embedded rat liver sections. The hepatocyte nuclei fell into two populations and showed either a crimson red or purple staining in frozen as well as paraffin sections. The heterogeneous staining of the rat heptocyte nuclei was also present when the tissue sections were stained by Methyl Green-Pyronin stain. The differing nuclear staining was present in the isolated nuclei also. The HBFP technique, therefore, appears potentially useful when applied to liver and other tissues as well. 相似文献
176.
The subcellular distribution and properties of guanylate cyclase was examined in preparations of normal rat renal cortex and Morris renal tumors MK2 and MK3. In normal kidney cortex about two-thirds of guanylate cyclase activity of homogenates was found in soluble fractions. With renal tumors the homogenate activity was less and the enzyme was equally divided between particulate and soluble fractions. The particulate enzyme in kidney cortex and tumors was associated with all particulate fractions. Triton X-100 increased the activity of all preparations. All preparations preferred Mn2+ as the sole cation. The stimulatory effects of Ca2+ on soluble enzyme and inhibitory effects on particulate activity were similar with preparations of renal cortex and tumors. ATP inhibited all preparations. Soluble and particulate guanylate cyclases from renal cortex were activated several-fold with 1 mM NaN3. Preparations of tumor enzymes did not respond to NaN3. Thus, compared to normal renal cortex the subcellular distribution of guanylate cyclase and some of its properties are altered in preparations of renal tumors. 相似文献
177.
Summary In the Dashte-Arjan area near Shiraz, rock formations appear to control the distribution of various plant species. The Fars formation (Miocene) and the Asmari-Jahrom formation (Eocene-Oligocen) sediments are characterized by distinet plant species and life forms. Among the characteristic calciphytes of Asmari-Jahrom limestones are Astragalus acutus, Amygdalus lyciodes, Cerasus microcarpa, and Fraxinus rotundifolia. The Fars formation limestones are characterized by Astragulus gossypinus, Acantholimon flexuosum, Noaea mucronata and Phlomis bruguieri, Except for Glycrrhiza glabra, white and red marls seem to have similar species, such as Alhagi maurorum and Carthamus oxyacantha. Gypsum of Fars formation has Berberis integerrima and Rosa beggeriana. Various life forms have been distinguished and were found to be confined to different rock types as well.Nomenclature of species is given in table 1.We are greately indebted to Dr. P.H. Davis and Prof. G. Pontecorvo F.R.S. for critically reading this paper and making some invaluable suggestions. We are grateful to the University Research Grant Commission for providing us a grant for this work. We are also indebted to the Dean, College of Arts & Sciences, Pahlavi University, Shiraz, Iran for providing us with a vehicle during this work. 相似文献
178.
A quantitative and qualitative survey of the indigenous Endogone population in wheat field soil and vesicular-arbuscular mycorrhiza in wheat roots as influenced by season and by the stage of development of the wheat plant was made. The number of Endogone spores in wheat field soil remained relatively unchanged in winter until January during the period of maximum root growth. The extent of formation of arbuscules was influenced by the stage of development of the wheat plants. 相似文献
179.
180.
Khan NA 《Molecular & general genetics : MGG》1975,136(1):55-61
Temperature-sensitive mutants affecting maltose utilization in the yeast Saccharomyces cerevisiae have been isolated. Two such mutants although failing to ferment maltose at the restrictive temperature, have normal induced level of maltase. The third mutant (UNT-37) not only failed to ferment maltose but has 5-6 fold less induced level of maltase at the restrictive temperature than the parental strain. The genetic control mechanisms of maltase induction and maltose utilization have been discussed. 相似文献