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11.
12.
Josef B. Keller 《Plant Systematics and Evolution》1872,22(10):335-337
Ohne Zusammenfassung 相似文献
13.
Several previously unavailable parameters of adenosine 3':5'-monophosphate have been determined. The molar extinction coefficient at pH 7.0 is 1.38 X 10(-4), the aqueous solubility at pH 7.0 is 0.0236 M and the diffusion coefficient is 4.44 X 10(-6) cm2/s. 相似文献
14.
Evelyn Fox Keller 《Biology & philosophy》1987,2(4):383-396
In much of the discourse of evolutionary theory, reproduction is treated as an autonomous function of the individual organism — even in discussions of sexually reproducing organisms. In this paper, I examine some of the functions and consequences of such manifestly peculiar language. In particular, I suggest that it provides crucial support for the central project of evolutionary theory — namely that of locating causal efficacy in intrinsic properties of the individual organism. Furthermore, I argue that the language of individual reproduction is maintained by certain methodological conventions that both obscure many of the problems it generates and serve to actively impede attempts to redress those difficulties that can be identified. Finally, I suggest that inclusion of the complexities introduced by sexual reproduction — in both language and methodology — may radically undermine the individualist focus of evolutionary theory.I am indepted to the Rockefeller Foundation for a Humanities Fellowship that supported this research during the spring of 1986. I am also grateful to Richard Lewontin, Diane Paul, and Lisa Lloyd for many extremely helpful conversations. 相似文献
15.
Manfred Keller Andras Seregi Georg Hertting Rolf Jackisch 《Neurochemistry international》1987,10(4):433-443
Prostaglandin (PG) and thromboxane B2 (TXB2) biosynthesis was studied in cultured astrocytes from neonatal rat brain hemispheres. After two weeks of cultivation, prostanoids were formed with the spectrum: PGD2 > TXB2 > PGF2 > PGE2, as measured by specific radioimmunoassays. Under basal conditions PGD2 biosynthesis (9.55 ng/mg protein/15 min) was in the same order of magnitude as the sum of the other prostanoids. The formation of prostanoids was stimulated in a concentration dependent manner (up to 6–10 fold) by the calcium ionophore A 23187 (0.01–10 μM) as well as by melittin (0.01–5 μg/ml), phospholipase A2 (10–40 U/ml) and phospholipase C (0.01–1 U/ml). Basal and evoked PG and TXB2 biosynthesis depended on the availability of Ca2+, as demonstrated in Ca2+ free incubation medium containing Na2EDTA (1 μM), or with verapamil (100 μM) and 3,4,5-trimethoxybenzoic acid-8-(diethylamino)-octylester-HCl (TMB-8, 1–100 μM). Indomethacin (10 μM), mepacrine (100 μM) and p-bromophenacylbromide (50 μ M) inhibited basal and evoked PG formation. Thin-layer chromatography (TLC) detection after incubation of the cells with [3H]arachidonic acid (1 μCi/ml, for 60 min) confirmed the results obtained by radioimmunoassay. Incubation of [3H]arachidonic acid labelled cells with inonophore or phospholipases, followed by lipid extraction and TLC, showed that A 23187 liberated [3H]arachidonic acid predominantly from phosphatidylethanolamine, whereas phospholipase A2 and C reduced mainly the labelling of the phosphatidyl-inositol/-choline fraction. Potassium depolarization of the cells did not enhance prostanoid formation. Similarly, drugs with affinity to - or β-adrenoceptors, or to dopamine-, 5-hydroxytryptamine-, muscarine-, histamine-, glutamate-, aspartate-, GABA, adenosine- and opioid-receptors failed to stimulate prostanoid biosynthesis. Also compounds like angiotensin, bradykinin and thrombin were ineffective in this respect.
In conclusion, our results confirm that cultured astrocytes possess the complete pattern of enzymes necessary for prostanoid formation and hence might play a crucial role in brain prostanoid biosynthesis. Stimulation of prostanoid biosynthesis involves Ca2+-dependent activation of phospholipase A2, cyclooxygenase reaction and further PG metabolism. However, the endogenous stimulus for enhanced prostanoid synthesis in the brain still has to be established. 相似文献
16.
Successful infection of the common marmoset (Callithrix jacchus) with human varicella-zoster virus. 总被引:1,自引:0,他引:1 下载免费PDF全文
P J Provost P M Keller F S Banker B J Keech H J Klein R S Lowe D H Morton A H Phelps W J McAleer R W Ellis 《Journal of virology》1987,61(10):2951-2955
The common marmoset, Callithrix jacchus, can be infected with human varicella-zoster virus (VZV), both wild-type strain KMcC and attenuated vaccine strain Oka/Merck. Infection was accomplished with either whole-cell-associated or cell extract VZV by combined oral-nasal-conjunctival application and was characterized by substantial and persistent anti-VZV antibody responses. The infectivity of VZV for marmosets was destroyed by treatment of inocula with heat or UV light. Diluted inocula with as few as 40 PFU/ml were infectious for marmosets. The lungs were demonstrated to be a major site of viral replication; both the presence of viral antigens and signs of pneumonia were demonstrated in lung tissues. Four serial passages of VZV KMcC were carried out in C. jacchus by a process of in vitro isolation and culturing of VZV from infected lung tissue and reapplication of the cultured isolates to fresh animals. The isolated viruses were identified as VZV both serologically and by restriction endonuclease analyses. The C. jacchus infectivity model should prove useful for determining the efficacy of subunit and live recombinant VZV vaccines as well as for the study of zoster. 相似文献
17.
Separation of multiple components of HeLa cell nuclear extracts required for pre-messenger RNA splicing 总被引:16,自引:0,他引:16
Components essential for nuclear pre-messenger RNA splicing have been partially purified from HeLa cell nuclear extracts by chromatography on DEAE-Sepharose, heparin-Sepharose, Mono Q, and Mono S. We have obtained six fractions which, when combined, efficiently splice a synthetic adenovirus 2 major late RNA substrate in vitro. All fractions contain components that support the formation of splicing intermediates (the cleaved 5' exon and the intron-exon 2 lariat). At least one of the fractions also contains an activity that is essential for the second step in the splicing reaction, namely cleavage at the 3' splice site and exon ligation. Two of the fractions are enriched in the major small nuclear ribonucleoprotein particles U1, U2, U4/U6, and U5. They participate in the formation of the splicing complexes which precedes the cleavage and ligation reactions. The remaining four fractions appear to contain protein factors, as suggested by their resistance to micrococcal nuclease. 相似文献
18.
Actinomycin synthetases. Multifunctional enzymes responsible for the synthesis of the peptide chains of actinomycin 总被引:6,自引:0,他引:6
U Keller 《The Journal of biological chemistry》1987,262(12):5852-5856
Two enzymes were purified from actinomycin-synthesizing Streptomyces chrysomallus which could be identified as peptide synthetases involved in the biosynthesis of actinomycin. Actinomycin synthetase II activates the first two amino acids of the peptide chains of the peptide lactone antibiotic, threonine and valine (or isoleucine), as thioesters via their corresponding adenylates. It is a single polypeptide chain of Mr 225,000. Similarly, actinomycin synthetase III activates proline, glycine, and valine (the remaining three amino acids in the antibiotic) as thioesters and is a single polypeptide chain of about Mr 280,000. It also carries the methyltransferase function(s) for N-methylation of thioesterified glycine and valine. In addition, it catalyzes the formation of cyclo(sarcosyl-N-methyl-L-valine) from glycine, L-valine, and S-adenosyl-L-methionine at the expense of ATP. Although the cell-free synthesis of the peptide lactone was not as yet accomplished, the data provide evidence that together with the 4-methyl-3-hydroxyanthranilic acid-activating enzyme (now designated as actinomycin synthetase I) all amino acid-activating protein components of the actinomycin-synthesizing enzyme complex are identified. 相似文献
19.
Michael A. Keller 《Entomologia Experimentalis et Applicata》1987,43(1):55-59
Walking speeds of female Trichogramma exiguum Pinto & Platner were fastest on maize and soybean (12 cm/min), intermediate on tomato (8 cm/min), and slowest on woolly mullein, Verbascum thapsus (3 cm/min). Similarly, rates of turning along the paths of walking T. exiguum were smallest on maize (median angle=0°±15°), intermediate on soybean and tomato, and greatest on V. thapsus (median angle=30°±15°). Leaf trichome density and morphology influenced walking behavior. Walking was slowed and flight initiation delayed for T. exiguum walking on Amaranthus hybridus leaves compared to either maize or filter paper. When inundative releases are conducted, the effects of plant surfaces on searching rates and arrestment should be considered in determining release rates of Trichogramma spp.
Résumé La vitesse de marche a été déterminée en lâchant des individus sur chaque substrat végétal et en traçant leur parcours sur une plaque de verre placée à 9 mm au dessus du sujet. Les déviations angulaires de portions successives des tracés, longues de 1 mm, ont été utilisées pour mesurer les taux de changement de direction. Dans une deuxième expérience, des individus ont été lâchés au milieu d'une cercle de 40 mm de diamètre sur chaque substrat et les temps écoulés avant l'envol ou pour atteindre le bord du cercle à la marche ont servi à évaluer respectivement la propension au vol et la vitesse de déambulation.Les vitesses de marche ont été plus rapides sur maïs et soja (12 cm/min), moyennes sur tomate (8 cm/min) et les plus lentes sur Verbascum thapsus (Scrophulariaceae) (3 cm/min). De le même façon, les angles de changement de direction au cours des marches effectuées par T. exiguum ont été plus petits sur maïs, moyens sur soja et tomate, et plus grands sur V. thapsus. Chez T. exiguum marchant sur des feuilles d'Amaranthus hybridus L. (Amaranthaceae), la marche a été plus lente et l'envol plus tardif que sur maîs ou papier filtre.Lors de lâchers inondatifs, les effets des surfaces végétales sur les vitesses d'exploration et d'arrêt devraient être pris en compte pour déterminer les vitesses de lâcher des Trichogramma spp.相似文献
20.