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31.
Kenneth B. Storey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(3):373-380
Summary Wood frogs,Rana sylvatica, were sampled after freezing at –4°C (a short time course from 2 to 70 min after the appearance of the freezing exotherm) and thawing (20 h at 3°C after 70 min of freezing) and the regulation of liver glycolysis with respect to cryoprotectant glucose synthesis was examined. Within 5 min of the initiation of freezing, cryoprotectant concentrations in blood and liver had begun to increase. This was correlated with a rapid rise in the levels of hexose monophosphates in liver, including a 2.5 fold increase in glucose-6-P and 10 fold rise in fructose-6-P contents within the first 5 min post-exotherm. Contents of fructose-1,6-P2, fructose-2,6-P2, triose phosphates, P-enolpyruvate, and pyruvate did not significantly change over the course of freezing. Thawing sharply reduced the levels of hexose monophosphates in liver but raised P-enolpyruvate content by 2.3 fold. Changes in the contents of glycolytic intermediates over the freeze/thaw course are consistent with an inhibitory block of glycolysis at phosphofructokinase during freezing in order to facilitate a rapid glycogenolysis and production of cryoprotectant; during thawing, however, glycolysis appears to be inhibited at the level of pyruvate kinase.Possible regulatory control of cryoprotectant synthesis by covalent modification of liver glycolytic enzymes was examined. Glycogenolysis during freezing was facilitated by an increase in the percentage of glycogen phosphorylase in the activea (phosphorylated) form and also by an increase in the total amount (a+b) of enzyme expressed. For phosphofructokinase, kinetic changes as a result of freezing included a 40% reduction inK
m
for fructose-6-P, a 60% decrease inK
a
for fructose-2,6-P2, and a 2 fold increase in I50 for ATP. These changes imply a freezing-induced covalent modification of the enzyme but are not, apparently, the factors responsible for inhibition of glycolytic flux at the phosphofructokinase locus during glucose synthesis. Kinetic parameters of pyruvate kinase were not altered over the freeze/thaw course. 相似文献
32.
Nicolas Mermod Juan L. Ramos Amos Bairoch Kenneth N. Timmis 《Molecular & general genetics : MGG》1987,207(2-3):349-354
33.
We have cloned and characterized three distinct alpha-globin haplotypes obtained from inbred strains of the mouse, Mus domesticus. We report here the complete nucleotide sequence of the six alpha-globin genes that the haplotypes contain. Our analysis of these genes and those from one other previously described haplotype indicates that recurrent gene conversion events have played a major role in their history. The pattern of nucleotide substitutions suggests that conversions have occurred both within and between haplotypes. Limited segments of coding and noncoding DNA have been involved in these gene conversion events. In two of the haplotypes, the nonallelic genes of each maintain DNA sequence identity over discrete intervals and encode the same alpha-globin polypeptide. On the other hand, the coding regions of some genes have accumulated replacement changes that result in distinct alpha-globins. In one instance, these changes appear to reflect positive selection of advantageous mutations. 相似文献
34.
Guadalupe Albarrán Kenneth E. Collins Carol H. Collins 《Journal of molecular evolution》1987,25(1):12-14
Summary Calcium carbonate labeled with carbon-14 was self-irradiated by means of the -decay of its carbon-14. A number of products containing one or two carbon atoms were identified by high performance liquid chromatography. Formic and oxalic acids were produced in relatively high yields, while glyoxylic, glycolic, and acetic acids, as well as formaldehyde and methanol, were formed in lower yields. These results support the suggestion that carbonates subjected to ionizing radiation could have been a source of carbon for organic synthesis on the primitive earth. 相似文献
35.
36.
Sami Ahmad Kenneth E. Kirkland Gary J. Blomquist 《Archives of insect biochemistry and physiology》1987,6(2):121-140
Direct evidence is presented for the role of a cytochrome P-450 monooxygenase (called mixed-function oxidase, or polysubstrate mono-oxygenase, PSMO) in the metabolism of the sex pheromone (Z)-9-tricosene to its corresponding epoxide and ketone in the housefly. A secondary alcohol, most likely an intermediate in the conversion of the alkene to the ketone, was also tentatively identified. The results of in vivo and in vitro experiments showed that the PSMO inhibitors, piperonyl butoxide (PB) and carbon monoxide, markedly inhibited the formation of epoxide and ketone from (9,10-3H) (Z)-9-tricosene. An examination of the relative rates of (Z)-9-tricosene metabolism showed that males exhibited a higher rate of metabolism than females with the antennae of males showing the highest activity of any tissue/organ examined. The major product from all tissues/organs was the epoxide. Data from experiments with subcellular fractions showed that the microsomal fraction had the majority of enzyme activity, which was strongly inhibited by PB and CO and required NADPH and O2 for activity. A carbon monoxide difference spectrum with reduced cytochrome showed maximal absorbance at 450 nm and allowed quantification of the cytochrome P-450 in the microsomal fraction of 0.410-nmol cytochrome P-450 mg?1 protein. Interaction of (Z)-9-tricosene with the cytochrome P-450 resulted in a type I spectrum, indicating that the pheromone binds to a hydrophobic site adjacent to the heme moiety of the oxidized cytochrome P-450. 相似文献
37.
Maintenance of innate feeding preferences by a polyphagous insect despite ingestion of applied deleterious chemicals 总被引:1,自引:0,他引:1
Kenneth F. Raffa 《Entomologia Experimentalis et Applicata》1987,44(3):221-227
The question of whether the appearance of a novel deleterious chemical in a preferred host plant could alter the relative degree of preference by a polyphagous insect during its lifetime was considered. The behavioral preference of fall armyworm, Spodoptera frugiperda (J. E. Smith), for corn (Zea mays L.) over red kidney bean Phaseolus spp. was quantified in a two-way choice test, and followed by a no-choice test in which the same larvae were fed either treated or untreated corn. Each treatment consisted of one of 15 compounds, including 13 naturally occurring allelochemicals and two synthetic insecticides. None of the test chemicals had any inherently deterrent effect at the rates tested. Deleterious effects on the larvae during exposure included reduced growth, reduced size, irritancy, and in some cases death. After this exposure the two way choice test was repeated. All test compounds failed to elicit a change in relative preference during the final two-way choice test. However, larvae exposed to gossypol and chrysanthemum monocarboxylic acid ester fed less than expected during the latter stages of no-choice conditions. The degree of aversion learning by each larva was related to the degree of prior sickness it had experienced.
Résumé Nous avons examiné si l'introduction d'une substance chimique nocive dans la plante-hôte préférée pouvait modifier la hiérarchie des choix durant le reste de la vie d'un insecte phytophage. Le comportement de préférence de Spodoptera frugiperda pour le maïs (Zea mays) vis à vis des Phaseolus, a été quantifié dans un dispositif à choix binaire, ont suivi des expériences au cours desquelles les chenilles devaient s'alimenter, soit sur maïs sain, soit sur maïs traité. Chaque essai concernait un composé chimique (15 au total), 13 étant des substances allélochimiques naturelles, 2 des insecticides de synthèse. Aux concentrations étudiées, aucun des produits n'a eu d'effet dissuasif. Les effets nocifs pendant l'exposition sur les chenilles comprenaient une croissance et une taille réduites, une irritation et, dans quelques cas, la mort. Aucune des expériences de choix binaire, avec des chenilles ayant subi cette exposition, n'a modifié les préférences. Cependant les chenilles, qui avaient été exposées au gossypol ou à l'acide monocarboxylique éthyl ester de chrysanthemum, ont consommé moins pendant les stades ultérieurs que ce que l'on pouvait attendre en absence de choix. Le degré d'aversion acquis par chaque chenille dépendait de l'importance des maux qu'elle avait subis précédemment.相似文献
38.
R S Reid A L Stuart S V Gupta L J Latimer B L Haug J S Lee 《Nucleic acids research》1987,15(10):4325-4335
Synthetic DNAs were prepared containing 6-methyl adenine (m6A) in place of adenine and 5-ethyl uracil (Et5U) or 5-methoxymethyl uracil (Mm5U) in place of thymine. All three modifications destabilized duplex DNAs to varying degrees. The binding of ethidium was studied to analogues of poly[d(AT)]. There was no evidence of cooperative binding and the "neighbour exclusion rule" was obeyed in all cases although the binding constant to poly[d(m6AT)] was approximately 6 fold higher than to poly[d(AT)]. 31P NMR spectra were recorded in increasing concentrations of CsF. Poly[d(AEt5U)] showed two well-resolved signals separated by 0.55 ppm in 1 M CsF compared to 0.32 ppm for poly[d(AT)] under identical conditions. In contrast, poly[d(AMm5U)] and poly[d(m6AT)] showed two signals separated by 0.28 ppm and 0.15 ppm respectively, only when the concentration of CsF was raised to 2 M. The signals for poly[d(AT)] in 2 M CsF were better resolved and were separated by 0.41 ppm. These results suggest that minor modifications to the bases may have conformational effects which could be recognized by DNA-binding proteins. 相似文献
39.
Summary Two species of predatory beetles that locate their prey, Ips pini, by responding to its aggregation pheromone have different chiral preferences to ispdienol than does the herbivore. This suggests that chiral disparity may provide some escape for bark beetles from predation, and that geographic variation in herbivore communication systems may be partially due to predator — imposed selection pressures. These results also suggest ways in which the semiochemical and biological control of North America's most damaging group of forest insects can be improved. 相似文献
40.
Kenneth A. Marx Ray Kruger Michael J. Clarke 《Molecular and cellular biochemistry》1989,86(2):155-162
The goal of this study is to establish the nature of pentammineruthenium(III) binding to DNA in intact mouse liver nuclei. Also, we wish to determine whether the nucleosomal organization of mouse chromatin has a substantial effect on the relative Ru(III) binding levels of internucleosomal and nucleosomal core DNA. These questions are important because ammineruthenium compounds share chemical and biological properties with the cis-dichlorodiammineplatinum(II) or cisplatin chemotherapeutic agent. Therefore, they represent a potential class of new chemotherapeutic agents. We find that in intact nuclei the predominant DNA binding site for pentammineruthenium(II), followed by air oxidation to pentammineruthenium(III), is N-7 guanine, as is the case with cisplatin. Also, the Ru(III) distribution between internucleosomal and nucleosomal core DNA was found to be nearly identical as probed with three non-specific deoxyribonucleases. 相似文献