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排序方式: 共有213条查询结果,搜索用时 31 毫秒
1.
The effect of myotoxin a on the thermotropic phase behavior of aqueous dispersions of dimyristoyl phosphatidylcholine (DMPC) and dimyristoyl phosphatidylserine (DMPS) was examined using differential scanning calorimetry (DSC). Myotoxin a significantly altered the normal phase behavior of DMPC in a concentration dependent fashion. This effect is perturbed by Ca2+ and is sensitive to ionic strength and pH. High concentrations of toxin eliminate the characteristic pretransition associated with the polar head group of DMPC. They also increase the temperature of the main gel-to-liquid crystal transition from 23 degrees C to 32-35 degrees C. At low concentrations of toxin, the first visible effect is upon the pretransition which is split into two components that diminish with time. The main transition is less affected at low toxin concentrations, although the magnitude of the transition is reduced while it is simultaneously shifted to higher temperatures. The main transition is also split into multiple components. The toxin also had pH specific effects on the phase behavior of DMPS. Above physiological pH (8.5) the normal transition of DMPS at 36-38 degrees C was split in the presence of myotoxin a and new components appeared centered at 31 degrees C and 35 degrees C. These observations are consistent with reports that the skeletal muscle membrane system is the major site of the myonecrotic effect of myotoxin a. 相似文献
2.
Conformational analysis of PKI(5-22)amide, the active inhibitory fragment of the inhibitor protein of the cyclic AMP-dependent protein kinase. 总被引:4,自引:0,他引:4 下载免费PDF全文
J Reed J S De Ropp J Trewhella D B Glass W K Liddle E M Bradbury V Kinzel D A Walsh 《The Biochemical journal》1989,264(2):371-380
Fourier-transform i.r. spectroscopy, 1H-n.m.r. spectroscopy and X-ray scattering were used to study the conformation and shape of the peptide PKI(5-22)amide, which contains the active site of the inhibitor protein of the cyclic AMP-dependent protein kinase [Cheng, Van Pattern, Smith & Walsh (1985) Biochem. J. 231, 655-661]. The X-ray-scattering solution studies show that the peptide has a compact structure with Rg 0.9 nm (9.0 A) and a linear maximum dimension of 2.5 nm (25A). Compatible with this, Fourier-transform i.r. and n.m.r. determinations indicate that the peptide contains approx. 26% alpha-helix located in the N-terminal one-third of the molecule. This region contains the phenylalanine residue that is one essential recognition determinant for high-affinity binding to the protein kinase catalytic site. 相似文献
3.
Calmodulin and troponin C structures studied by Fourier transform infrared spectroscopy: effects of Ca2+ and Mg2+ binding 总被引:3,自引:0,他引:3
Fourier transform infrared (FTIR) spectroscopy has been used to examine the conformationally sensitive amide I' bands of calmodulin and troponin C. These are observed to undergo a sequence of spectroscopic changes which reflect conformational rearrangements that take place when Ca2+ is bound. Calmodulin and troponin C show similar though not identical changes on Ca2+ binding, and the effect of Mg2+ on troponin C is quite different from that of Ca2+. Both proteins show absorption maxima in the amide I' region at 1644 cm-1 which is significantly lower in frequency than has been generally observed for proteins that contain a high percentage of alpha-helix. It is proposed that an unusually high proportion of the helices in the structures of these proteins are distorted from the normal alpha-helical configuration such that the carbonyl stretching frequencies are lowered. It is further proposed that the shift to lower frequency is due to backbone carbonyl groups in the distorted helices that form strong hydrogen bonds with solvent molecules. A decrease in intensity at 1654 cm-1, the normal frequency assignment for alpha-helical structure, is observed as Ca2+ binds to calmodulin and troponin C. This suggests that Ca2+ binding results in a net decrease in "normal" alpha-helix conformation. There is a corresponding increase in intensity of the band at 1644 cm-1, possibly due to an increase in distorted helix content, allowing for a net increase in helix consistent with circular dichroism estimates of the Ca2+-dependent changes in helix content in calmodulin. 相似文献
4.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献
5.
Interaction of myotoxin a with artificial membranes: Raman spectroscopic investigation 总被引:1,自引:0,他引:1
Myotoxin a from the venom of Crotalus viridis viridis (prairie rattlesnake) is a small protein which is responsible for myonecrosis. It is a basic protein with 42 amino acid residues of known sequence. Three disulfide bonds give it a highly compact structure. Microscopic examination of the toxin's effects reveals that the most pronounced and earliest visible damage occurs intracellularly, in the sarcoplasmic reticulum membrane system of skeletal muscle. A better understanding of its mechanism of action is therefore of particular interest. The interaction of myotoxin a with artificial membranes (multibilamellar phospholipid dispersions) was investigated by using dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylserine (DMPS). Two regions of the Raman spectrum were examined for information: the C-H stretching region between 2800 and 3000 cm-1 and the C-C stretching region between 1000 and 1300 cm-1. The effects of myotoxin a on the thermotropic phase behavior of the artificial membranes were determined. This was done by monitoring three structurally sensitive Raman intensity ratios, I2932/2880, I2880/2850, and I1088/1126. It was found that myotoxin alpha destabilized the ordered structure of the gel phase of phospholipid bilayers. This effect was seen with both DMPC and DMPS. The pretransition of DMPC was perturbed by myotoxin a, while the main gel to liquid-crystal phase transition temperature was decreased. The effect of myotoxin a on the phase behavior of DMPS was found to be pH dependent with the least effect observed at low pH values. These results suggest the involvement of negatively charged phosphate groups of phospholipids in the interaction of myotoxin a with artificial membranes. 相似文献
6.
Biochemical pathways in prokaryotes can be traced backward through evolutionary time 总被引:10,自引:0,他引:10
For the first time, a credible prokaryotic phylogenetic tree is being
assembled by Woese and others using quantitative sequence analysis of
oligonucleotides in the highly conservative rRNA. This provides an
evolutionary scale against which the evolutionary steps that led to the
arrangement and regulation of contemporary biochemical pathways can be
measured. This paper presents an emerging evolutionary picture of aromatic
amino acid biosynthesis within a large superfamily assemblage of
prokaryotes that is sufficiently developed to illustrate a new perspective
that will be applicable to many other biochemical pathways.
相似文献
7.
Erythrocyte survival studies were conducted on eight, normal, healthy, 1-year-old male specific-pathogen-free cats using both chromium-51 and iron-59 simultaneously. The chromium-51 procedure gave a half-life value of 11.1 +/- 0.9 days. This was considerably lower than would be expected on the basis of the experimentally determined iron-59 erythrocyte survival time of 51.2 +/- 14.9 days. The results of this study indicated that there was considerable loss of the chromium-51 label in the cat other than that from senescence alone. An analysis of the chromium-51 disappearance curve indicated that there were two exponential disappearance rates for the chromium-51 label and, in the absence of cell death, approximately 67% of the label was lost with a rate constant of 0.02 per day and 33% was lost with a rate constant of 0.1 per day. An equation is presented which models the loss of chromium-51 label which could be used to calculate erythrocyte survival from a chromium-51 disappearance curve. Blood volume measurements, hemograms, bone marrow differential results, and iron kinetic values also were determined and the results presented. While a reasonable approximation of the erythrocyte life span could be made by correcting the chromium-51 values for losses other than senescence, the iron-59 procedure would be the preferred method in cats. 相似文献
8.
The relative potencies of cholecystokinin (CCK-33) and its carboxyl terminal octapeptide (CCK-8) for stimulation of amylase release from rat pancreatic acini was measured. Porcine CCK-33 and synthetic CCK-8 were initially subjected to high pressure liquid chromatography to assess purity. Concentrations of each peptide were determined by amino acid analysis. The relative immunoreactivities of CCK-33 and CCK-8 were compared using an antibody that recognizes the common carboxyl terminus of these forms. This antibody bound CCK-8 and CCK-33 with nearly equal affinity. The relative potencies of CCK-33 and CCK-8 were then measured by comparing their abilities to stimulate amylase release from isolated rat pancreatic acini. Statistical analysis of the relative potencies of the two hormones indicated that CCK-8 was 36% more potent than CCK-33 in this assay system. These data suggest that differences in biological activities between large and small forms of CCK are not as great as previously reported. 相似文献
9.
A cDNA clone encoding glucose-dependent insulinotropic peptide (GIP) was identified that consisted of 34 bp of 5' untranslated sequence, an open reading frame of 432 bp and 115 bp in the 3' untranslated region. The deduced amino acid sequence revealed a 144 amino acid preprohormone consisting of a 43 amino acid N-terminal extension including a signal peptide, a 42 amino acid hormone, and a 59 amino acid C-terminal extension. Rat GIP differs from the human hormone by two amino acid substitutions: arginine for histidine at position 18 and leucine for isoleucine at position 40. A single mRNA from small intestine of approximately 800 bases was identified on Northern blot analysis in equivalent amounts in proximal and distal small intestine. 相似文献
10.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献