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971.
Chirashree Choudhury Arun Kumar Ray Samir Bhattacharya Shelley Bhattacharya 《Environmental Biology of Fishes》1993,36(3):319-324
Synopsis
Anabas testudineus were treated with non lethal levels of metacid-50 (0.106 ppb) and carbaryl (1.66 ppm) for 90 days covering the pre-spawning and spawning phases of the annual reproductive cycle. The main purpose of the present work was to identify the effects of metacid-50 and carbaryl on the gonado somatic index (GSI) and ovarian and plasma estrogen level. There was no alteration in GSI until 15 days, initiating the inhibition on day 20 which further intensified from 20 to 90 days of exposure. Plasma and ovarian estrogen level significantly increased up to 15 days of exposure followed by a decline till the end of the experiment. It is noteworthy that the effect of pesticides on GSI is reflected in the ovarian estrogen level. This highlights the fact that at short-term exposures the nonlethal levels of pesticides have no inhibitory effect while at long-term exposure, the pesticides have potent inhibitory effect on the reproduction of fish. 相似文献
972.
Baseline impedance (Z0) and resistivity of blood were higher for marmots than reported for other species. The transthoracic impedance method was compared to dye dilution and electromagnetic flowmeter procedures for estimation of cardiac output of seven marmots at a range of flows from 40 to 400 ml/min. There was a low, positive, but significant correlation (r = 0.566) found in comparison to dye dilution at outputs measured by the impedance method exceeding 120 ml/min. Correlation was better (r = 0.905) in the comparison between impedance and flowmeter methods.It was concluded that transthoracic impedance provides data that are sufficiently accurate for chronic measurements of stroke volume and cardiac output of this species. The method has the additional advantage of supplying EGG and respiratory data without supplemental connections to the animal preparations. 相似文献
973.
974.
Partial suppression of an Escherichia coli TonB transmembrane domain mutation (ΔV17) by a missense mutation in ExbB 总被引:5,自引:5,他引:0
Ray A. Larsen Michael G. Thomas Gwendolyn E. Wood† Kathleen Postle 《Molecular microbiology》1994,13(4):627-640
Active transport of vitamin B12 and Fe(III)-siderophore complexes across the outer membrane of Escherichia coli appears to be dependent upon the ability of the TonB protein to couple cytoplasmic membrane-generated protonmotive force to outer membrane receptors. TonB is supported in this role by an auxiliary protein, ExbB, which, in addition to stabilizing TonB against the activities of endogenous envelope proteases, directly contributes to the energy transduction process. The topological partitioning of TonB and ExbB to either side of the cytoplasmic membrane restricts the sites of interaction between these proteins primarily to their transmembrane domains. In this study, deletion of valine 17 within the amino-terminal transmembrane anchor of TonB resulted in complete loss of TonB activity, as well as loss of detectable in vivo crosslinking into a 59 kDa complex believed to contain ExbB. The ΔV17 mutation had no effect on TonB export. The loss of crosslinking appeared to reflect conformational changes in the TonB/ExbB pair rather than loss of interaction since ExbB was still required for some stabilization of TonBΔV17. Molecular modeling suggested that the ΔV17 mutation caused a significant change in the predicted conserved face of the TonB amino-terminal membrane anchor. TonBΔV17 was unable to achieve the 23 kDa proteinase K-resistant form in lysed sphaeroplasts that is characteristic of active TonB. Wild-type TonB also failed to achieve the proteinase K-resistant configuration when ExbB was absent. Taken together these results suggested that the ΔV17 mutation interrupted productive TonB–ExbB interactions. The apparent ability to crosslink to ExbB as well as a limited ability to transduce energy were restored by a second mutation (A39E) in or near the first predicted transmembrane domain of the ExbB protein. Consistent with the weak suppression, a 23 kDa proteinase K-resistant form of TonBΔV17 was not observed in the presence of ExbBA39E. Neither the ExbBA39E allele nor the absence of ExbB affected TonB or TonBΔV17 export. Unlike the tonBΔV17 mutation, the exbBA39E mutation did not greatly alter a modelled ExbB transmembrane domain structure. Furthermore, the suppressor ExbBA39E functioned normally with wild-type TonB, suggesting that the suppressor was not allele specific. Contrary to expectations, the TonBδV17, ExbBA39E pair resulted in a TonB with a greatly reduced half-life (≅ 10 min). These results together with protease susceptibility studies suggest that ExbB functions by modulating the conformation of TonB. 相似文献
975.
Aude Rauscent Didier Le Ray Marie-Jeanne Cabirol-Pol Keith T. Sillar John Simmers Denis Combes 《Journal of Physiology》2006,100(5-6):317-327
Metamorphosis in the anuran frog, Xenopus laevis, involves profound structural and functional transformations in most of the organism's physiological systems as it encounters a complete alteration in body plan, habitat, mode of respiration and diet. The metamorphic process also involves a transition in locomotory strategy from axial-based undulatory swimming using alternating contractions of left and right trunk muscles, to bilaterally-synchronous kicking of the newly developed hindlimbs in the young adult. At critical stages during this behavioural switch, functional larval and adult locomotor systems co-exist in the same animal, implying a progressive and dynamic reconfiguration of underlying spinal circuitry and neuronal properties as limbs are added and the tail regresses. To elucidate the neurobiological basis of this developmental process, we use electrophysiological, pharmacological and neuroanatomical approaches to study isolated in vitro brain stem/spinal cord preparations at different metamorphic stages. Our data show that the emergence of secondary limb motor circuitry, as it supersedes the primary larval network, spans a developmental period when limb circuitry is present but not functional, functional but co-opted into the axial network, functionally separable from the axial network, and ultimately alone after axial circuitry disappears with tail resorption. Furthermore, recent experiments on spontaneously active in vitro preparations from intermediate metamorphic stage animals have revealed that the biogenic amines serotonin (5-HT) and noradrenaline (NA) exert short-term adaptive control over circuit activity and inter-network coordination: whereas bath-applied 5-HT couples axial and appendicular rhythms into a single unified pattern, NA has an opposite decoupling effect. Moreover, the progressive and region-specific appearance of spinal cord neurons that contain another neuromodulator, nitric oxide (NO), suggests it plays a role in the maturation of limb locomotor circuitry. In summary, during Xenopus metamorphosis the network responsible for limb movements is progressively segregated from an axial precursor, and supra- and intra-spinal modulatory inputs are likely to play crucial roles in both its functional flexibility and maturation. 相似文献
976.
31P nuclear magnetic resonance (NMR) measurements (at 121.5 MHz and 5 degrees C) were made on complexes of 3-phosphoglycerate kinase with ADP and 3-P-glycerate. Addition of Mg(II) to E.ADP shifts the alpha-P signal downfield by 3.8 ppm such that the alpha-P signal superimposes that for beta-P(E.MgADP). Such a shift is atypical among the Mg(II)-nucleotide complexes with other ATP-utilizing enzymes. This shift allowed the determination that enzyme bound ADP is saturated with Mg(II) for [Mg(II)]/[ADP] = 3.0--similar to that reported for ATP complexes with this enzyme (B.D. Ray and B.D. Nageswara Rao, Biochemistry 27, 5574 (1988]. This parallel behavior suggests that ADP binds at two sites on the enzyme as does ATP with disparate Mg(II) affinities. 31P relaxation times in E.MnADP.vanadate.3-P-glycerate and E.CoADP.vanadate.3-P-glycerate complexes indicate that these are long-lived, tightly bound complexes. 31P chemical shift measurements on diamagnetic complexes (with Mg(II] revealed three signals in the 2-5 ppm region (attributable to 3-P-glycerate) only upon addition of all the components necessary to form the E.MgADP.vanadate.3-P-glycerate complex. Subsequent sequestration of Mg(II) from the complex with excess EDTA reversed the Mg(II) induced effects on the ADP signals but did not cause coalescence of the three signals seen in the 2-5 ppm region. Addition of excess sulfate to dissociate these complexes from the enzyme resulted in a single resonance of 3-P-glycerate. The use of arsenate in place of vanadate yielded very similar results. These results suggest that, in the presence of MgADP, vanadate or arsenate, and 3-P-glycerate, the enzyme catalyzed the formation of multiple structurally distinguishable complexes that are stable on the enzyme and labile off the enzyme. 相似文献
977.
UDP-glucose 4-epimerase from Saccharomyces fragilis is rapidly inactivated by heating at 42 degrees C for 7 min and at 45 degrees C for 4 min. The effector site, specific for sugar phosphates, is destroyed still earlier. The enzyme is inactivated by the dissocation of NAD from it leaving the dimeric structure unaffected. It can be reactivated by mercaptoethanol and NAD, both of which are essential for reactivation, and NAD becomes associated with the dimeric protein moiety. 相似文献
978.
979.
We have analyzed the contributions made by maternal and zygotic genes to the establishment of the expression patterns of four zygotic patterning genes: decapentaplegic (dpp), zerknüllt (zen), twist (twi), and snail (sna). All of these genes are initially expressed either dorsally or ventrally in the segmented region of the embryo, and at the poles. In the segmented region of the embryo, correct expression of these genes depends on cues from the maternal morphogen dorsal (dl). The dl gradient appears to be interpreted on three levels: dorsal cells express dpp and zen, but not twi and sna; lateral cells lack expression of all four genes; ventral cells express twi and sna, but not dpp and zen. dl appears to activate the expression of twi and sna and repress the expression of dpp and zen. Polar expression of dpp and zen requires the terminal system to override the repression by dl, while that of twi and sna requires the terminal system to augment activation by dl. The zygotic expression patterns established by the maternal genes appear to specify autonomous domains that carry out independent developmental programs, insofar as mutations in the genes that are expressed ventrally do not affect the initiation or ontogeny of the expression patterns of the genes that are expressed dorsally, and vice versa. However, interactions between the zygotic genes specific to a particular morphological domain appear to be important for further elaboration of the three levels specified by dl. Two of the genes, dpp and twi, are unaffected by mutations in any of the tested zygotic dorsal-ventral genes, suggesting that dpp and twi are the primary patterning genes for dorsal ectoderm and mesoderm, respectively. 相似文献
980.
Christopher A. Scholin Roman Marin III Peter E. Miller Gregory J. Doucette Christine L. Powell Paul Haydock Judith Howard Jason Ray 《Journal of phycology》1999,35(6):1356-1367
Large-subunit ribosomal RNA-targeted probes for Pseudo-nitzschia australis Frenguelli, P. multiseries (Hasle) Hasle, P. pseudodelicatissima (Hasle) Hasle, and P. pungens (Grunow) Hasle were applied to cultured and natural samples using whole-cell and sandwich hybridization. Testing of the latter method is emphasized here, and technique refinements that took place during 1996–1997 are documented. Application of the sandwich hybridization test showed that the signal intensity obtained for a given number of target cells remained constant as batch cultures of these organisms progressed from active through stationary growth phases. This suggests that cellular rRNA content for each target species remained relatively stable despite changes in growth state. Application of whole-cell and sandwich hybridization assays to natural samples showed that both methods could be used to detect wild P. australis, P. pseudodelicatissima, and to a lesser degree P. multiseries, but detection of P. pungens was prone to error. A receptor-binding assay for domoic acid (DA) enabled detection of this toxin activity associated with a particulate fraction of the plankton and provided a context in which to view results of the rRNA probe tests. In one case, the probe for P. australis cross-reacted with P. cf. delicatissima. The sample that contained the latter species also contained a low amount of DA activity. Under certain field conditions, results of whole-cell and sandwich hybridization tests disagreed. Detailed analysis of selected field samples illustrates how such situations arose. Collectively, the rRNA probe and toxin analyses suggest that manifestation of DA in the environment is possible in the absence of readily recognizable intact cells. 相似文献