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101.
William A. Bonner Neal E. Blair Frederick M. Dirbas 《Origins of life and evolution of the biosphere》1981,11(1-2):119-134
Our earlier experiments are briefly reviewed, involving the abiotic generation of optical activity by exposure of DL-amino acids to various chiral physical forces. The enantiomeric enrichments so obtained were low, however, and additional experiments were undertaken with the objective of abiotically enhancing such small enantiomeric excesses. DL Mixtures of leucine N-carboxy anhydride gave enantiomerically enriched polymers on partial polymerization, while valine NCA mixtures behaved oppositely. Leucine polymers were also found to hydrolyze stereoselectively, providing for additional enantiomenic enhancement. A repetitive sequence of partial polymerization-hydrolysis steps is suggested as a possible mechanism for the abiotic genesis of optically enriched polypeptides on the primitive Earth. 相似文献
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From February 1972 to August 1974 ten immatureCebus albifrons monkeys were weighed and vaginal swabbing performed at monthly or shorter intervals to determine age and weight at the onset
of puberty. The average weight (±S.E.M.) at birth and at puberty was 226±5.8 g and 1,617±32.45 g, respectively. The average
age at puberty was 3.59±0.17 years. The average weight velocity for all ten monkeys shows the maximum rate of weight gain
to occur shortly after birth and decrease rapidly to its smallest prepubertal increment at nine months of age (weaning). From
nine months there is a post-weaning weight spurt which reaches its greatest velocity at an average age of 15 months. Thereafter,
the weight velocity decreases to its lowest level. Individual weight velocity curves of each of the ten animals show a slight
prepubertal weight spurt which is not obvious in the average growth curve. 相似文献
107.
Chin Y. Yeh Peter P. Fu Frederick A. Beland Ronald G. Harvey 《Bioorganic chemistry》1978,7(4):497-506
molecular orbital theoretical calculations performed on the anti and syn diolepoxides (1 and 2) of the potent carcinogen benzo[a]pyrene provide insight into the molecular structure and reactivity of these mutagenic and carcinogenic hydrocarbon metabolites. Hydrogen-bonded interaction between the 7-HO proton and the epoxide oxygen atom of 2 is shown to be absent in the normal semichair conformation of the tetrahydro ring, (H…O bond distance = 2.7 Å), but is energetically favored in a somewhat distorted puckered structure (H…O bond distance = 1.7 Å). Unexpectedly, internal H-bonding alters the relative electron density at C9 and C10, leading to prediction of the former as the more electrophilic center. Since all reactions of 2 take place exclusively at C10, transannular H-bonding is concluded not to contribute significantly to the structure of 2. Diolepoxide reactions with both weak and strong nucleophiles and with DNA are discussed and the mechanisms interpreted in terms of molecular structure as determined by the theoretical calculations. 相似文献
108.
Cytotoxic T lymphocytes in DBA/2 mice harboring L5178Y cells in a tumor-dormant state 总被引:1,自引:0,他引:1
Mark A. Marsili Michael K. Robinson Gary A. Truitt E. Frederick Wheelock 《Cancer immunology, immunotherapy : CII》1983,16(1):59-64
Previous experiments have demonstrated a temporal relationship between the decline of cytotoxic T lymphocyte (CTL) activity in the peritoneal cavity of DBA/2 mice harboring L5178Y cells in a tumor-dormant state and the appearance of ascitic tumors. Some tumor-dormant mice remain clinically normal for many weeks after the decline of CTL activity, and this activity can be rapidly restimulated by an IP inoculation of irradiated L5178Y cells. We report here that the peritoneal cells from many tumor-dormant mice can be stimulated to cytolytic activity in vitro when cultured for 4 days either with or without the addition of irradiated L5178Y cells. Peritoneal cell populations which cannot be stimulated in vitro can suppress the generation of CTL in those populations which can be stimulated. The tumor-dormant state may terminate when suppressor cells in the peritoneal cavity of tumor-dormant mice inhibit the generation of CTL activity and permit tumor cells to produce an ascitic tumor. 相似文献
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Methionine sulfoxide is transported into purified intestinal and renal brush border membrane vesicles from rabbit by an Na+-dependent mechanism and is accumulated inside the vesicles against the concentration gradient. Both in intestine and kidney, the rate of transport is enhanced with increasing concentrations of Na+ in the external medium. Increasing the Na+ gradient reduces the apparent Kt for methionine sulfoxide without causing any change in Vmax. With an outward K+ gradient (vesicle > medium), valinomycin stimulates the Na+-gradient-dependent transport of methionine sulfoxide in the kidney, showing the electrogenicity of the transport process. A number of amino acids inhibit methionine sulfoxide transport in both the intestine and kidney. An enzymatic activity capable of reducing methionine sulfoxide to methionine is present in the intestinal mucosa, renal cortex and liver. The activity is highest in renal cortex and lowest in intestine. The methionine sulfoxide-reducing activity is stimulated by NADH, NADPH, glutathione and dithiothreitol and the potency of the stimulation is in the order: dithiothreitol > NADPH > glutathione > NADH. 相似文献