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11.
Forbes SH; Hogg JT; Buchanan FC; Crawford AM; Allendorf FW 《Molecular biology and evolution》1995,12(6):1106-1113
We compared genotypes at eight (AC)n microsatellite loci in domestic sheep
(Ovis aries) and wild Rocky Mountain bighorn sheep (O. canadensis). The
domestic sheep had greater genetic variation, higher allele-size variances,
and larger allele sizes than the wild sheep. Accumulating evidence from
higher taxonomic comparisons shows that these parameters are biased if
microsatellite loci are selected in one taxon and used in another. Our
results demonstrate similar biases between congeneric species. We compared
standard measures of genetic variation, differentiation, and distance
within and between species (H, D, FST) to newer measures based on
allele-size variance (SW, SB, RST). The size-based distances better
detected species-level divergence, but standard measures better
distinguished allopatric populations. Empirical calibration of these
measures at the subspecies level is needed to establish their useful
ranges.
相似文献
12.
Aus einer größeren Gruppe von Barbus conchonius, die mit Merkurochrom behandelt worden waren, verloren viele anschließend das schwarze Hautpigment. Je 20 depigmentierte und normal gebliebene Tiere wurden 10 Monate danach auf ihre Reaktionen gegenüber Futter, Futterduft, reines Wasser, Schreckstoff, Erschütterung und starke Bewegung vor dem Becken geprüft. An je vier Einzeltieren wurde die Zeit gemessen, die sie brauchten, um Futter zu finden. Ferner wurden an mehreren kleinen Gruppen beider Sorten das Verhalten gegenüber zugesetzten fremden oder wieder-zugesetzten Tieren aus der Gruppe untersucht. Auf chemische Nahrungssignale und Erschütterungen des Beckens hin schwimmen normale Tiere nach oben, depigmentierte nach unten; auf Futter schwammen auch die normalen gleich wieder zum Boden. Auf die anderen Reize reagierten nur die normalen Tiere deutlich. Den depigmentierten fehlten manche typischen Verhaltensweisen (Schwarm-Stehen, manche Flucht- und die typischen Angriffsweisen). Alle diese Ausfälle und das an Blindfische erinnernde Nahrungsuchen am Boden werden als ?Verhaltensregressionen” zusammengefaßt, deren mögliche Ursachen erörtert sind. Die vergleichbaren morphologischen, physiologischen und ethologischen Merkmale blinder Höhlenfischarten lassen sich wahrscheinlich auf die gleiche Weise erklären. 相似文献
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14.
Olfactory sensitivity in tsetse flies: a daily rhythm 总被引:3,自引:0,他引:3
The diurnal tsetse Glossina morsitans morsitans bites especially in early
morning and late afternoon; around midday feeding is at a low. In
laboratory apparatus that measures the amount of locomotion under constant
conditions over the photophase, the flies display a similar patterning of
activity levels. The profile of daily rhythms for G. morsitans reported in
the literature includes a number of motor and sensory motor systems that
fluctuate cophasically. Lacking is a study on the patterning of the senses'
response levels. In this paper we present the first instance of a daily
modulation in the sense of smell. We stimulated the antennae with
concentration series of host-derived odours and measured the spiking rate
of cells at different times during the photophase. The
concentration-response curves suggest that the sensitivity of antennal
olfactory cells flows in parallel with the other daily rhythms. This was
also reflected in electroantennograms (EAGs). The electroantennography was
extended to G. fuscipes fuscipes, whose level of spontaneous locomotor
activity--instead of following a U- shaped pattern--rises gradually over
the photophase. Again, the EAGs appeared to parallel the species' locomotor
activity. What we believe happens is that the organism tones down the
sensitivity of its odour receptors during periods of anticipated inactivity
for reasons of economy.
相似文献
15.
Aitor Hernandez-Ortega Matthew G. Quesne Soi Bui Dominic P. H. M. Heuts Roberto A. Steiner Derren J. Heyes Sam P. de Visser Nigel S. Scrutton 《The Journal of biological chemistry》2014,289(12):8620-8632
Dioxygenases catalyze a diverse range of chemical reactions that involve the incorporation of oxygen into a substrate and typically use a transition metal or organic cofactor for reaction. Bacterial (1H)-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (HOD) belongs to a class of oxygenases able to catalyze this energetically unfavorable reaction without any cofactor. In the quinaldine metabolic pathway, HOD breaks down its natural N-heteroaromatic substrate using a mechanism that is still incompletely understood. Experimental and computational approaches were combined to study the initial step of the catalytic cycle. We have investigated the role of the active site His-251/Asp-126 dyad, proposed to be involved in substrate hydroxyl group deprotonation, a critical requirement for subsequent oxygen reaction. The pH profiles obtained under steady-state conditions for the H251A and D126A variants show a strong pH effect on their kcat and kcat/Km constants, with a decrease in kcat/Km of 5500- and 9-fold at pH 10.5, respectively. Substrate deprotonation studies under transient-state conditions show that this step is not rate-limiting and yield a pKa value of ∼7.2 for WT HOD. A large solvent isotope effect was found, and the pKa value was shifted to ∼8.3 in D2O. Crystallographic and computational studies reveal that the mutations have a minor effect on substrate positioning. Computational work shows that both His-251 and Asp-126 are essential for the proton transfer driving force of the initial reaction. This multidisciplinary study offers unambiguous support to the view that substrate deprotonation, driven by the His/Asp dyad, is an essential requirement for its activation. 相似文献
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17.
Leferink NG Heuts DP Fraaije MW van Berkel WJ 《Archives of biochemistry and biophysics》2008,474(2):292-301
The VAO flavoprotein family is a rapidly growing family of oxidoreductases that favor the covalent binding of the FAD cofactor. In this review we report on the catalytic properties of some newly discovered VAO family members and their mode of flavin binding. Covalent binding of the flavin is a self-catalytic post-translational modification primarily taking place in oxidases. Covalent flavinylation increases the redox potential of the cofactor and thus its oxidation power. Recent findings have revealed that some members of the VAO family anchor the flavin via a dual covalent linkage (6-S-cysteinyl-8α-N1-histidyl FAD). Some VAO-type aldonolactone oxidoreductases favor the non-covalent binding of the flavin cofactor. These enzymes act as dehydrogenases, using cytochrome c as electron acceptor. 相似文献
18.
ChitO (chito-oligosaccharide oxidase) from Fusarium graminearum catalyses the regioselective oxidation of N-acetylated oligosaccharides. The enzyme harbours an FAD cofactor that is covalently attached to His94 and Cys154. The functional role of this unusual bi-covalent flavin-protein linkage was studied by site-directed mutagenesis. The double mutant (H94A/C154A) was not expressed, which suggests that a covalent flavin-protein bond is needed for protein stability. The single mutants H94A and C154A were expressed as FAD-containing enzymes in which one of the covalent FAD-protein bonds was disrupted relative to the wild-type enzyme. Both mutants were poorly active, as the k(cat) decreased (8.3- and 3-fold respectively) and the K(m) increased drastically (34- and 75-fold respectively) when using GlcNac as the substrate. Pre-steady-state analysis revealed that the rate of reduction in the mutant enzymes is decreased by 3 orders of magnitude when compared with wild-type ChitO (k(red)=750 s(-1)) and thereby limits the turnover rate. Spectroelectrochemical titrations revealed that wild-type ChitO exhibits a relatively high redox potential (+131 mV) and the C154A mutant displays a lower potential (+70 mV), while the H94A mutant displays a relatively high potential of approximately +164 mV. The results show that a high redox potential is not the only prerequisite to ensure efficient catalysis and that removal of either of the covalent bonds may perturb the geometry of the Michaelis complex. Besides tuning the redox properties, the bi-covalent binding of the FAD cofactor in ChitO is essential for a catalytically competent conformation of the active site. 相似文献
19.
Interspecific predation of spiders was studied in the laboratory in view of possible competition in the wild. Certain species killed other species even if handicapped by smaller size. Thirty eight spider species were involved in such a relationship and their predatory relationships were significantly reliable and transitive ('linear' or 'non-triangular'). A theridiid species (Theridion tinctum) showed the highest rank in terms of killing seven 'beta species', i.e. species capable of killing at least one alien species of larger size than themselves. Another theridiid (Steatoda grossa) obtained the second rank by killing five beta species. Experiments in both the wild and laboratory may, further, investigate other factors than body size that may be relevant to competition, such as behaviour-related characteristics (e.g. web structure and biting speed) and ecological factors (e.g. different susceptibilities of the species to parasite or predator attack). 相似文献
20.
Discovery, characterization, and kinetic analysis of an alditol oxidase from Streptomyces coelicolor 总被引:1,自引:0,他引:1
Heuts DP van Hellemond EW Janssen DB Fraaije MW 《The Journal of biological chemistry》2007,282(28):20283-20291
A gene encoding an alditol oxidase was found in the genome of Streptomyces coelicolor A3(2). This newly identified oxidase, AldO, was expressed at extremely high levels in Escherichia coli when fused to maltose-binding protein. AldO is a soluble monomeric flavoprotein with subunits of 45.1 kDa, each containing a covalently bound FAD cofactor. From sequence alignments with other flavoprotein oxidases, it was found that AldO contains a conserved histidine (His(46)) that is typically involved in covalent FAD attachment. Covalent FAD binding is not observed in the H46A AldO mutant, confirming its role in covalent attachment of the flavin cofactor. Steady-state kinetic analyses revealed that wild-type AldO is active with several polyols. The alditols xylitol (K(m) = 0.32 mm, k(cat) = 13 s(-1)) and sorbitol (K(m) = 1.4 mm, k(cat) = 17 s(-1)) are the preferred substrates. From pre-steady-state kinetic analyses, using xylitol as substrate, it can be concluded that AldO mainly follows a ternary complex kinetic mechanism. Reduction of the flavin cofactor by xylitol occurs at a relatively high rate (99 s(-1)), after which a second kinetic event is observed, which is proposed to represent ring closure of the formed aldehyde product, yielding the hemiacetal of d-xylose. Reduced AldO readily reacts with molecular oxygen (1.7 x 10(5) m(-1) s(-1)), which confirms that the enzyme represents a true flavoprotein oxidase. 相似文献