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11.
Divalent cation involvement in the action of Clostridium perfringens type A enterotoxin. Early events in enterotoxin action are divalent cation-independent 总被引:15,自引:0,他引:15
B A McClane A P Wnek K I Hulkower P C Hanna 《The Journal of biological chemistry》1988,263(5):2423-2435
Clostridium perfringens type A enterotoxin (CPE) is a membrane-active cytotoxin. There are a number of recognized early steps in CPE cytotoxicity including binding of CPE to a protein receptor, insertion of CPE into membranes, and CPE-mediated induction of changes in membrane permeability for small molecules such as ions and amino acids. Further support for the existence of these early steps and further characterization of these events are presented in this report. We now report that these early steps in CPE action are largely independent of extracellular divalent cations. It is also shown that 3H-nucleotide release, known to be a later CPE effect, is Ca2+-dependent. A model for CPE cytotoxicity is suggested involving CPE action as a two-step process with Ca2+-independent early steps and Ca2+-dependent late steps. 相似文献
12.
13.
Antoine M. Hakim Marie J. Arrieta Bernard A. Cooper† Hanna M. Pappius 《Journal of neurochemistry》1984,42(6):1582-1587
There is considerable debate on the role of folate in CNS function. Recent work indicates that folate deficiency may affect CNS serotonin metabolism, and clinical studies describe many consequences of such a deficiency. On the other hand some workers maintain that folate deficiency alone causes CNS abnormalities. We maintained rats, through dietary deprivation, at folate levels below 4 ng/ml for more than 6 weeks and showed that at that time both their liver and brain folate levels were significantly reduced. We then studied their local cerebral glucose utilization (LCGU) using the [14C]deoxyglucose technique. This method assesses cerebral function by measuring regional metabolic activity. We also determined LCGU in rats given the same diet but replenished with folate (folate control) and in others given free access to commercially available food (normal controls). Our results show that this degree of folate deficiency has no effect on cerebral function. This contrasts with the focal suppression of LCGU we previously reported in a model of vitamin B12 deficiency. 相似文献
14.
Erythrocyte diphosphopyridine nucleotidase (NADase) in paroxysmal nocturnal hemoglobinuria 总被引:1,自引:0,他引:1
15.
E Breslow R T Co P Hanna T Laborde 《International journal of peptide and protein research》1989,34(1):21-27
Circular dichroism was used to compare the environment of peptides bound to native and des 1-8 neurophysin in order to further elucidate the role of the neurophysin 1-8 sequence in peptide-binding. A very large positive ellipticity (approximately 6000 deg cm2 dmol-1), shown earlier to be induced in tyrosine at position 2 of peptides bound to the native protein, was determined by the present study to be paralleled by similar induced changes in tyrosine at peptide position 1. Deletion of the neurophysin 1-8 sequence led to loss of half of the induced optical activity at peptide positions 1 and 2 and changes in binding-induced optical activity in the protein, the latter partially assignable to protein disulfides. In the mononitrated native and des 1-8 proteins, the optical activity of neurophysin Tyr-49, a residue at the peptide-binding site, was reduced by 80% in complexes of the des 1-8 protein relative to those of the native protein. The results suggest a role for neurophysin Arg-8 in modulating the optical activity at the binding site by directly placing a charge proximal to the binding site and/or by altering binding site conformation. The data provide the first unambiguous evidence of a difference in the environment of bound peptide between the native and des 1-8 proteins. 相似文献
16.
The formation of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO)/.OH adduct of the spin trap DMPO has been reported to occur through nucleophilic addition of water in the presence of aqueous ferric chloride (K. Makino, T. Hagiwara, A. Hagi, M. Nishi, and A. Murakami, 1990, Biochem. Biophys. Res. Commun. 172, 1073-1080). Due to the serious implications of these findings with respect to many spin trapping studies, the suitability of DMPO as a hydroxyl radical spin trap was studied in typical Fenton systems. Using 17O-enriched water, we show conclusively that nucleophilic addition of water occurs at the nitrone carbon (or C-2 position) of DMPO in the presence of either Fe or Cu ions. Furthermore, our results demonstrate that this nucleophilic reaction is a major pathway to the DMPO/.OH adduct, even during the reaction of Fe(II) or Cu(I) with hydrogen peroxide. Primary alkoxyl adducts of DMPO also form in aqueous solution through nucleophilic addition in the presence of both Fe(III) and Cu(II). Attempts to obtain secondary and tertiary alkoxyl adducts by this mechanism were unsuccessful, possibly due to steric effects. When the reaction is carried out in various buffers, however, or in the presence of metal ion chelators, nucleophilic addition to DMPO from Fe(III) is effectively suppressed. Chelators also suppress the reaction with Cu(II). Hence, under most common experimental conditions in biochemical free radical research, nucleophilic addition to DMPO should not be of major concern. 相似文献
17.
Central Mechanisms of Pheromone Information Processing 总被引:1,自引:0,他引:1
An advantage of using pheromones in olfactory studies is thatthey are chemical signals for which receptor neurons are evolvedand thus elicite biologically relevant odour-information tobe processed in the brain. In many vertebrate and insect species,the olfactory system is separated into a mainand an accessory division, the latter mediatingpheromone information. In moths, the pheromone information isfirst processed in the brain in a large and sexually dimorphicstructure, the macroglomerular complex (MGC) of the antennallobe (AL). Also in vertebrates the pheromone information isprocessed in specific or modified glomerular complexes. Oneprinciple question is whether individual olfactory glomeruliare functional units, processing specific information concerningboth the chemical quality and spatiotemporal features of thestimulus, like the pheromone plume. Indeed it has been shownthat the axons of different pheromone-selective receptor neuronsproject into different MGC-glomeruli. Intracellular recordingsfrom the AL projection (output) neurons also show that informationabout single components of the pheromone blend is preservedin some output pathways, whereas other output neurons respondin a unique fashion to the blend. The information about interspecificsignals, which interrupts pheromone attraction, is processedin a specific MGC-glomerulus and is to a large extent kept separatedfrom the pheromone information throughout the AL. Many of theoutput neurons accurately encode changes in the temporal characteristicsof the stimulus. Chem. Senses 21: 269275, 1996. 相似文献
18.
Suppression of mutations in the core of the Tetrahymena ribozyme by spermidine, ethanol and by substrate stabilization. 总被引:1,自引:0,他引:1 下载免费PDF全文
We have previously described a collection of mutations in conserved residues of the core of the Tetrahymena self-splicing intron. Most of these single base substitutions have less than 10% of the activity of their parental intron derivative [Couture, S., et al., (1990) J. Mol. Biol., 215, 345-358]. We examined the effect of two agents known to stabilize RNA structure, spermidine and ethanol, on the activity of many of these mutant RNAs. In the presence of either 5 mM spermidine or 20% ethanol most substitution mutations were partially or completely suppressed. These conditions also increased the temperature optima of both wild-type and mutant ribozymes. In addition, we find that mutations are also suppressed by a high concentration of GTP, a substrate in the reaction which is bound specifically by the intron. Thus we observe a general suppression of mutations in an RNA enzyme (ribozyme) by spermidine, ethanol and by substrate stabilization. These results are consistent with the idea that most mutations destabilize the folded structure of the ribozyme and can be suppressed by any of a variety of stabilizing influences. 相似文献
19.
E. L. Lubbers L. Arthur W. W. Hanna P. Ozias-Akins 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(5):636-642
Two molecular markers, a RAPD (randomly amplified polymorphic DNA) and a RFLP/STS (restriction fragment length polymorphism/sequence-tagged site), previously were found associated with apomictic reproductive behavior in a backcross population produced to transfer apomixis from Pennisetum squamulatum to pearl millet. The occurrence of these molecular markers in a range of 29 accessions of Pennisetum comprising 11 apomictic and 8 sexual species was investigated. Both markers were specific for apomictic species in Pennisetum. The RFLP/STS marker, UGT 197, was found to be associated with all taxa that displayed apomictic reproductive behavior except those in section Brevivalvula. Neither UGT197 nor the cloned RAPD fragment OPC-04600 hybridized with any sexually reproducing representatives of the genus. The cloned C04600 was associated with 3 of the 11 apomictic species, P. ciliare, P. massaicum, and P. squamulatum. UGT197 was more consistently associated with apomictic reproductive behavior than OPC04600 or cloned C04600, thus it could be inferred that UGT197 is more closely linked to the gene(s) for apomixis than the cloned C04600. The successful use of these probes to survey other Pennisetum species indicates that apomixis is a trait that can be followed across species by using molecular means. This technique of surveying species within a genus will be useful in determining the relative importance of newly isolated markers and may facilitate the identification of the apomixis gene(s). 相似文献
20.
Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proponed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ. 相似文献