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21.
4β,5-Epoxy-5β-androstane-3,17-dione (), 17β-hydroxy-4β,5-epoxy-5β-androstan-3-one () and 17β-acetoxy-4β,5-epoxy-5β-androstan-3-one () were treated with anhydrous hydrogen fluoride in pyridine (70% solution) at 55° and yielded the corresponding 4-en-4-ols e.g. 4-hydroxy-4-androstene-3, 17-dione ().As the reaction temperature was lowered each epoxide formed a second product which, at ?75°, was the major component of the reaction mixture and was identified as the 5α-fluoro-4α-ol derivative of the parent enone, e.g. 4α-hydroxy-5-fluoro-5α-androstane-3,17-dione (). These fluorohydrins are thermally unstable, losing hydrogen fluoride.The acetates of the fluorohydrins were also prepared, characterized, and shown to be more stable than the parent alcohols. 相似文献
22.
W. A. Schroeder Darleen Powars Joan B. Shelton J. Roger Shelton J. B. Wilson T. H. J. Huisman Antranik A. Bedros 《Biochemical genetics》1982,20(11-12):1175-1187
After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal β and δ genes. 相似文献
23.
Females of the social wasp, Polistes annularis, nest in largeaggregations onriverside cliffs in central Texas. Aggregationsoccur where there is an overhang under which wasps build theirnests. Colony aggregations appear to occur partly because individualfemales do notdisperse far from the natal site where most coloniesare successful. In most taxa greater reproductive success nearthe natal nest site is related to unique physical features orto advantages ofbeing in a group. In P. annularis, the physicalfactors and not the social factors appear to be most important.Advantages to remaining near the natal nest site include protectionprovided by the cliff overhang from rain and afternoon sun.Central colonies are as likely to suffer predation as are peripheralcolonies, which indicates an absence of selfish herd advantagesto being in the center of the group. A cost of being in a denseaggregation is often increased reproductive competition, andthis is the case for P. annularis. Colonies in the center ofthe aggregation suffer high usurpation rates by unrelated femalesand in 1 of 3 years produced fewer reproductives than edge colonies. 相似文献
24.
Joan M. Herbers 《Journal of theoretical biology》1981,89(1):175-189
Reliability theory is used to explore the consequences of ant colony's foraging techniques for the evolution of individual competence. Five fundamental strategies are outlined according to Oster & Wilson (1978) and corresponding probabilities of food being returned to the nest are derived. The strategies differ in redundancy schemes and levels of worker reliability. Colony-level selection produces workers of imperfect competence. System reliability can be very high even when the workers are inept, if the foraging strategy is complex and redundant. Individual competence of foragers in a colony depends on diet breadth, caste polymorphism, and tempo. The implications of each variable for colony survival are discussed. 相似文献
25.
Joan S.Y. Ng Leslie D. Burtnick 《International journal of biological macromolecules》1982,4(4):215-218
Maleylation of lysine residues, nitration of tyrosine residues or modification with 2,3-butanedione or 1,2-cyclohexanedione of arginine residues on actin resulted in a loss of polymerizability of the modified actin. However, only lysine modification produced a complete loss of the deoxyribunuclease I inhibitory ability of actin at low degrees of modification. By the level of one modified lysine per actin monomer, the samples completely lost polymerizability and lost 65% of their inhibitory power against deoxyribonuclease I-catalysed hydrolysis of DNA. By two lysines modified per actin, all inhibitory activity was lost. One lysine residue on actin apparently overlaps both an actin action contact site and an actin-deoxyribnuclease 1 contact site, offering a suggestion as to how deoxyribonuclease I blocks actin polymerization. 相似文献
26.
Quantitative analysis of metabolite levels in normal human subjects by31P topical magnetic resonance
M. Joan Dawson 《Bioscience reports》1982,2(9):727-733
Conclusions The results we have obtained on forearm muscles of normal human subjects are complementary to those on isolated frog muscle and they lead, to the same conclusions. We are satisfied that our31P TMR measurements of [P-metabolites] in normal subjects are reliable, and we are now extending these methods for use in cases of degenerative muscular disorders (Edwards et al., 1982). Chemical estimates of [ADP] and [AMP] are not directly relevant to metabolic studies, and so an important contribution of NMR to the study of muscular mechanisms is its ability to estimate the concentrations of these metabolites that are free to take part in metabolic reactions. 相似文献
27.
28.
Janice Y. Chou Bruce D. Weintraub Saul W. Rosen Jacqueline Whangpeng Howard D. Sussman Joan R. Haughom J. C. Robinson 《In vitro cellular & developmental biology. Plant》1976,12(8):589-594
Summary Several cell lines, originally thought to be derived from a human placenta at term but possibly HeLa-contaminated, have been
studied. These cells secrete a protein indistinguishable immunochemically from the alpha subunit of chorionic gonadotropin
but not the beta subunit of chorionic gonadotropin or placental lactogen. Complete chorionic gonadotropin was detected but
amounted to less than 1% of the level of the alpha subunit. The cells also produce an alkaline phosphatase similar to placental
alkaline phosphatase in immunochemical, gel-electrophoretic, and heat-denaturation properties. They induce tumor growth when
inoculated into nude mice. These cells are aneuploid and have a model chromosome number of 66. The common HeLa karyologic
markers, designated 1, 2, and 3, and A-type glucose-6-phosphate dehydrogenase are present in these cells. HeLa cells have
not previously been shown to secrete theα subunit of hCG. 相似文献
29.
Superoxide dismutase in some obligately anaerobic bacteria 总被引:21,自引:0,他引:21
30.
Hamster lymph node and spleen cells can be stimulated to incorporate tritiated thymidine ([3H]TdR) in vitro under serum-free conditions by the proteases trypsin and chymotrypsin. Under similar conditions, thymocytes could be stimulated by concanavalin A (ConA) but not lipopolysaccharide (LPS) or the proteases. The subpopulation of cells responding to the proteases correlated with the cells responding to LPS on fractionation of spleen and lymph node cells on discontinuous bovine serum albumin (BSA) gradients or on nylon-wool columns. The stimulation induced by trypsin was completely blocked by soybean trypsin inhibitor (SBTI) while that induced by chymotrypsin was only partially blocked. The inhibition by SBTI of protease activation was not effective when added 24 h after initiation of stimulation. On the other hand, addition of clarified isologous serum to protease activated cultures after 24 h still lead to greater than 50% inhibition of [3H]TdR incorporation. 相似文献