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1.
Thiosulfate-cytochrome c-551 reductase derived from Chlorobiumthiosulfatophilum has been highly purified. The enzyme reduces cytochrome c-551 of C. thiosulfatophilum in the presence of thiosulfate while cytochrome c-555 of the organism is not reduced by the enzyme. Cytochrome c-555 reacts with the enzyme at an appreciable rate only in the presence of cytochrome c-551. However, the reduction rate of cytochrome c-551 by the enzyme is greatly enhanced on addition of a catalytic amount of cytochrome c-555. Therefore, cytochrome c-555 seems to function as an effector on thiosulfate-cytochrome c-551 reductase as well as it acts as the electron donor to the light-excited chlorobium chlorophylls.  相似文献   

2.
C D Fitch 《Life sciences》1977,21(10):1511-1514
Chloroquine-resistant P.berghei is as susceptible to chloroquine as chloroquine-susceptible P.berghei when adequately exposed for short periods of time (1 hour) invitro. In both cases 3.1 mM chloroquine causes a significant decrease in infectivity of the parasites whereas 0.31 mM chloroquine is without effect. Since there is no evidence that chloroquine has a peculiar mechanism of action invitro, these results support the hypothesis of inadequate exposure of intracellular parasites as the cause of chloroquine resistance.  相似文献   

3.
Two compounds were isolated from female Heliothisvirescens (Lepidoptera: Noctuidae) extracts and identified as cis-9-tetradecenal and cis-ll-hexadecenal. Together they elicit intense male H. virescnes response in laboratory tests and have attracted males in the field. Although cis-ll-hexadecenal is an H. zea sex pheromone, no evidence was obtained for cis-9-tetradecenal in H. zea.  相似文献   

4.
A novel synthesis of 16α-hydroxy-4-androstene-3,17-dione (3), 16α-hydroxy-4-androstene-3, 6,17-trione (4), 17β-amino-5-androsten-3β-ol (10) and 17β-amino-4-androsten-3-one (14) is described. 16α-Bromoacetoxy-4-androstene-3, 17-dione (5), 16α-bromoacetoxy-4-androstene-3, 6,17-trione (6) and 17β-bromoacetylamino-4-androsten-3-one (15) were synthesized as potentially selective irreversible inhibitors of androgen aromatases. 16α-Bromo-4-androstene-3,17-dione (1) and 16α-bromo-4-androstene-3, 6,17-trione (2) were converted to compounds 3 and 4 in 80–90% yield by controlled stereospecific hydrolysis using sodium hydroxide in aqueous pyridine. Reductive amination of 3β-hydroxy-5-androsten-17-one and 3-methoxy-3,5-androstadien-17-one (11) using ammonium acetate and sodium cyanohydridoborate (NaBH3CN) and a subsequent treatment with acid gave the amines 10 and 14 respectively, as a salt. The corresponding 17-imino compounds 9 and 13 were also isolated from the reaction mixtures when methanol was used as a solvent for the reaction. The 16α-hydroxyl compounds 3 and 4 and the 17β-amino compound 14 were con- verted to the corresponding bromoacetyl derivatives, 5, 6, and 15, with bromoacetic acid and N,N'-dicyclohexylcarbodiimide.  相似文献   

5.
The effects of 19-hydroxy-prostaglandins (19-OH-PGs) were tested invivo on the rabbit oviduct and uterus and on the rhesus monkey (Macacamulatta) uterus. The 19-OH-PGEs suppressed spontaneous oviductal and uterine activity in the rabbit. The qualitative effect on the rabbit oviduct of 19-OH-PGEs was similar to that of PGE2. However, the typical response of the rabbit uterus to PGE2 was an increase in muscle activity. With regard to the rabbit oviduct, 19(R)-OH-PGE2 was as potent as PGE2, but 19(S)-OH-PGE2 was approximately 12 as potent as PGE2. Based on the dose of 19-OH-PGEs usually required to cause a minimal suppression and the dose of PGE2 required to cause a minimal stimulation of rabbit uterine activity, 19(R)-OH-PGE2 was twice as potent as PGE2 while 19(S)-OH-PGE2 was 12 as potent as PGE2. Stimulatory effects on the rabbit oviduct and uterus were observed following administration of 19-OH-PGEs and PGF. The potency on the rabbit oviduct of 19(S)-OH-PGF was about 15 to 110 that of PGF; the potency of 19(R)-OH-PGF was about 110 to 120 that of PGF. Both 19-OH-PGFs were approximately 15 to 110 as potent as PGF on the rabbit uterus. At the doses tested 19-OH-PGFs were inactive on the monkey uterus. Thus, these compounds are at least 15 as active as PGF. In contrast, 19(R)-OH-PGE2 had approximately the same potency as PGE2 in stimulating monkey uterine activity; but 19(S)-OH-PGE2 was approximately 13 as potent as PGE2.  相似文献   

6.
Cooperativity in ligand binding: a new graphic analysis.   总被引:16,自引:0,他引:16  
When analyzing binding of ligands to macromolecules, the existence of site-site interactions complicates a straightforward interpretation of the binding parameters obtained through classical analytical methods, such as the Scatchard plot. For describing site-site interactions, we propose a new parameter, the average affinity of the receptor sites, K, calculated as (BF)/(Ro?B). Plotting K as a function of fractional occupancy (BRo), reveals that: (1) at very low occupancy a limiting high K is obtained (Ke) (“empty sites” conformation); (2) when the fraction of sites filled increases above a certain threshold, K begins to fall due to increasing site-site interactions until (3) a limiting low K (Kf) is obtained (“filled sites” conformation). This method has been successfully applied to the negative cooperativity of insulin receptors.  相似文献   

7.
The enantiomer selection in the nucleophilic addition reaction of optically active amines such as α-amino acid esters to phenylalanine and N-methylphenylalanine N-carboxyanhydride in m-dimethoxybenzene as a solvent has been investigated. Stereoselectivity between the amines and the N-carboxyanhydrides was found to change markedly according to the reaction conditions. This experimental finding is in contrast to the idea hitherto accepted that in the nucleophilic addition-type polymerization of α-amino acid N-carboxyanhydride the growing chain end reacts preferentially with one of the enantiomorphic N-carboxyanhydrides having the same configuration, and indicates the importance of the investigation of stereoselectivity in the N-carboxyanhydride polymerization using suitable model reactions. Most (S)-α-amino acid esters reacted preferentially with (R)-phenylalanine N-carboxyanhydride, and this type of stereoselectivity increased with the N-methylation of N-carboxyanhydride and with increasing bulkiness of the Cα substituent of α-amino acid esters (alanine < norleucine < leucine < valine). The relationship observed between the stereoselectivity and the structures of amines and N-carboxyanhydrides was explained satisfactorily in terms of the transition state model in which the interaction of N-carboxyanhydride nitrogen and α-amino acid ester carbonyl as well as the interaction of N-carboxyanhydride carbonyl and α-amino acid ester nitrogen was taken into account. (S)-Proline ethyl ester did not show enantiomer selectivity toward phenylalanine N-carboxyanhydride, but reacted preferentially with (S)-(N)-methylphenylalanine N-carboxyanhydride. for the reaction of proline ester with N-carboxyanhydride a transition-state model was proposed, which was different from the transition state model proposed for other α-amino acid esters. Some experiments were carried out to examine the transition-state models proposed. The implications of the present investigation in stereoselectivity in the nucleophilic addition-type polymerization of N-carboxyanhydride hitherto reported are discussed.  相似文献   

8.
9.
Repair deficiency in Escherichia coli UV-sensitive mutator strain uvr502   总被引:8,自引:0,他引:8  
The effect of ultraviolet irradiation (UV) has been studied in Escherichiacoli mutator UV-sensitive mutant uvr502, its uvrA6 derivative and wild-type strain. The uvr502 mutant is about 5 times more UV-sensitive than the uvr+ isogenic strain, but 3 times less sensitive than the uvrA6 single mutant. Cells of the uvr502 mutant are unable to rejoin the fragments of parental DNA formed after UV as a result of incision. The double mutant uvrA6uvr502 as well as the single uvrA6 mutant irradiated with UV is unable to introduce breaks into parental DNA. The extent of postreplication repair is essentially normal in the uvr502 cells. There is no significant difference between the uvr+ and uvr502 cells in the rate and extent of UV-induced DNA degradation.  相似文献   

10.
Coccidioidesimmits has been isolated from the guano of bats obtained beneath bat roosting places deep within deserted mine tunnels. Certain species of bats have been demonstrated to be susceptible to experimental infection by C.immitis. There is, however, a difference in the laboratory susceptibility between the species studied (Antrozouspallidus and Macrotuscalifornicus). Antrozouspallidus requires 8 times more arthrospores (400 as compared to 50) than does Macrotuscalifornicus to produce a defineable infection. Our cultures for C.immitis in the tissue of Antrozous produced colonies of the bacterium Serratiamarcescens. Because these tissues were handled under sterile conditions the presence of this red pigment (prodigiosin) producing bacterium was thought not the result of contamination. Prodigiosin suggests a possible mechanism for the apparent greatly reduced susceptibility to C. immitis found in the laboratory population of Antrozous. Skin and serological tests on bats were negative as were cultures of guano from experimentally infected bats and mice. It is speculated that infected dying bats that fall to the floor beneath their roosting sites may contaminate the guano. We of course realize that other animals (we have found Neotoma and Bassariscus rarely in these tunnels) may have tracked the fungus into these deep tunnel sites.  相似文献   

11.
A protein has been isolated from ovine hypothalamus on the basis of its ability to stimulate release of growth hormone by invitro cultures of dispersed pituitary cells. This protein has been identified as being myelin basic protein. With no similar biological activity invivo, myelin basic protein is thus to be recognized as a potentially interfering substance in any search for the physiological growth hormone releasing factor using invitro assay systems.  相似文献   

12.
Injections of prostaglandin E1 into the haemocoel of the marine arthropods Limuluspolyphemus, Homarusamericanus and Penaeusduorarum induced a behaviorally mediated fever (increase in preferred temperature, resulting in increased body temperature). The finding that PGE1 is pyorgenic to arthropods as well as to mammals suggests that arthropods can be used as simple experimental models for further investigations of the neuropharmacological role of prostaglandins in fever.  相似文献   

13.
Rhodotorucine A which induces mating tube formation of a cells in Rhodosporidiumtoruloides is metabolized rapidly by a cells. By use of labeled rhodotorucine A, the degradation was found to be proteolytic. Two peptide fragments Tyr-Pro-Glu-Ile-Ser-Trp-Thr-Arg and Asn-Gly-Cys(S-farnesyl) were identified as the metabolites. Proteolysis of the pheromone mainly occurred on the cell surface. Culture filtrate of a cells at log phase did not metabolize rhodotorucine A.  相似文献   

14.
The thymine derived quasimetacyclophane exist in two conformers a and b. The absorption spectra of a and b were evaluated and the conformational equilibrium in different solvents /H2O : EtOH/ were examined. The rate constant k?1 for reaction ba was established as well as Ea.  相似文献   

15.
The metabolism of drobuline has been examined in the dog, rabbit, rat, guinea pig and hamster. In the dog, unlike the other species, glucuronide conjugation is the major route of metabolism. The structure of the conjugate has been established as an O-glucuronide by isolation using HPLC following by field desorption mass spectral analysis. When the separate d- and l-isomers of drobuline were administered to a series of dogs the l-isomer reached plasma levels approximately three time higher than those of the d-isomer. Deuterium labeled drobuline was synthesized and resolved by multiple crystallizations of the malate salts. Racemic mixtures containing d6-d and h6-l drobuline and d6-l and h6-d drobuline were prepared and analyzed by GC-MS as the pentafluoropropionate derivatives. When either racemic mixture was administered to dogs (10 mg/kg, p.o.) the plasma levels of the l-isomer were found to be approximately three times those of the d-isomer. Using these deuterium labeled mixtures the disposition of the two isomers has been examined in the isolated perfused dog liver, in hepatocytes and isolated microsomes. The results indicate that the difference in plasma levels of the d- and l-isomers is not dependent upon stereospecific absorption or excretion but rather it is caused by metabolism of the d-isomer at a faster rate than that of the l-isomer.  相似文献   

16.
The 9,10-dihydrophenanthrene phenolic compound juncusol, from the marsh plant Juncusroemerianus, has been shown to be inhibitory to four species of naturally occurring Bacillus and to two ATCC species Bacillussubtilis and Staphylococcusaureus. Juncusol may regulate populations of bacillus bacteria in the marsh and has potential as an antimicrobial agent particularly to gram positive microorganisms.  相似文献   

17.
Chemically formylated Met-tRNAmMet and Met-tRNAfMet species from E.coli and yeast were tested for their capacity to serve as chain-initiators in a cell-free system from E.coli. In the presence of R 17 mRNA, initiation factors and E.coli ribosomes, all four Met-tRNAs could form functional initiation complexes as measured by ribosomal binding kinetics, fMet-puromycin formation and synthesis of a dipeptide fMet-Ala. Unformylated Met-tRNAfMet from E.coli displayed significantly less activity as a peptide chain-initiator than the formylated Met-tRNAmMet species from E.coli and yeast. Although the latter tRNAs were less effective initiators than the “physiological” initiator tRNAs, the data seem to indicate that a blocked α-amino group represents the major token of identification by which Met-tRNA is admitted to function in E.coli peptide chain initiation.  相似文献   

18.
Ether-containing lipids of methanogenic bacteria   总被引:7,自引:0,他引:7  
Acid-hydrolysis of the phospholipid fraction of Methanobacterium thermoautotrophicum, Methanobacterium formicicum and Methanospirillum hungatii demonstrated the presence of two neutral lipid products. Characterization of these lipids resulted in their identification as dialkyl glyceryl ether and diglycerol tetraethers. The ether-linked alkyl chains were identified as the 20- and 40-carbon branched chains for the diether and tetraether, respectively. M. thermoautotrophicum and M. formicicum were also characterized by the presence of acid-stable phospholipid components.  相似文献   

19.
A new enzyme, which catalyzes the transfer of a methyl group to tRNA to form 5-methylaminomethyl-2-thiouridylate, was isolated from E.coli by a procedure including affinity chromatography. The purified enzyme was nearly homogeneous upon disc electrophoresis. Using methyl-deficient tRNAGlu of E.coli as substrate, the 5-methylaminomethyl-2-thiouridylate residue synthesized was mostly found in the anticodon loop, showing a coincidence of the modification site invitro with that invivo.  相似文献   

20.
Both pairs of dl-ll-desoxy- and dl-13-cis-erythro-15, 16-dihydroxyprostaglandins have been synthesized via 1,4-conjugate additions of an appropriately functionalized cis-vinyl cuprate to the requisite cyclopentenone. These prostaglandin analogs are considerably less potent than PGE2 as gastric secretion inhibitors or as bronchodilators.  相似文献   

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