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1.
2.
This paper reports an experiment designed to demonstrate that the calf lung can be sensitized to a specific respirable challenge following parenteral immunization with a nonliving antigen (human serum albumin). The possibility that immune-mediated injury could subsequently interfere with nonspecific mucosal defenses was also investigated by infecting calves with Pasteurella haemolytica after the antigen challenge and assessing pulmonary clearance of the organism. The results indicated that specific aerosol challenge produces reversible signs of respiratory hypersensitivity and that persistence of incidental infection in the upper respiratory tract is potentiated. Since the calves were sensitized by an immunization regime which imitated conventional vaccination, this study highlights the potential dangers of inactivated parenteral respiratory vaccines. 相似文献
3.
Membrane peptidases in the pig choroid plexus and on other cell surfaces in contact with the cerebrospinal fluid. 总被引:5,自引:2,他引:3
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A comprehensive survey of 11 peptidases, all of which are markers for renal microvillar membranes, has been made in membrane fractions prepared from pig choroid plexus. Two fractionation schemes were explored, both depending on a MgCl2-precipitation step, the preferred one having advantages in speed and yield of the activities. The specific activities of the peptidases in the choroid-plexus membranes were, with the exception of carboxypeptidase M, lower than in renal microvillar membranes: those of aminopeptidase N, peptidyl dipeptidase A ('angiotensin-converting enzyme') and gamma-glutamyltransferase were 3-5-fold lower, those of aminopeptidase A and endopeptidase-24.11 were 12-15 fold lower, and those of dipeptidyl peptidase IV and aminopeptidase W were 50-70-fold lower. Carboxypeptidase M had a similar activity in both membranes. Alkaline phosphatase and (Na+ + K+)-activated ATPase were more active in the choroid-plexus membranes. No activity for microsomal dipeptidase, aminopeptidase P and carboxypeptidase P could be detected. Six of the peptidases and (Na+ + K+)-activated ATPase were also studied by immunoperoxidase histochemistry at light- and electron-microscopic levels. Endopeptidase-24.11 and (Na+ + K+)-activated ATPase were uniquely located on the brush border, and the other two peptidases appeared to be much more abundant on the endothelial lining of microvessels. Dipeptidyl peptidase IV and aminopeptidase W were also detected in microvasculature. Pial membranes associated with the brain and spinal cord also stained positively for endopeptidase-24.11, aminopeptidase N and peptidyl dipeptidase A. The immunohistochemical studies indicated the subcellular fractionation did not discriminate between membranes derived from epithelial cells (i.e. microvilli) and those from endothelial cells. The possible significance of these studies in relation to neuropeptide metabolism and the control of cerebrospinal fluid production is discussed. 相似文献
4.
The adenylyl cyclase system of the yeast Saccharomyces cerevisiae contains the CYR1 polypeptide, responsible for catalyzing formation of cAMP from ATP, and two RAS polypeptides, responsible for stimulation of cAMP synthesis by guanine nucleotides. We have obtained rabbit antibodies that recognize the CYR1 protein. Antibodies were raised against synthetic oligopeptides and against a recombinant beta-galactosidase/CYR1 fusion protein. These antibodies have allowed the identification of the CYR1 gene product as a 205 kDa protein. Treatment with trypsin (2 micrograms/ml) reduced the size of the CYR1 protein from 205 to 155 kDa and produced an activated enzyme which no longer responded to guanine nucleotides. This result is consistent with a model in which adenylyl cyclase activity is regulated by an inhibitory domain near the amino-terminus of the CYR1 protein. This model is further supported by the finding that adenylyl cyclase activity is also markedly elevated and unresponsive to guanine nucleotides in mutant yeast strains that express only the carboxy-terminal half of the CYR1 protein. Treatment with high trypsin concentrations (greater than 10 micrograms/ml) caused release of adenylyl cyclase activity from the membrane. Comparison of immunoreactive CYR1 fragments released by trypsin and membrane bound genetically altered proteins suggests that the CYR1 protein is attached to the membrane via a separate trypsin sensitive anchoring protein rather than via a membrane anchoring domain. 相似文献
5.
N-Methylformamide extracts of acid-treated precipitated VFe protein of the V-nitrogenase of Azotobacter chroococcum are yellow-brown in colour and contain vanadium, iron and acid-labile sulphur in the approximate proportions 1:6:5. E.p.r. spectra of the extracts exhibit a weak signal with g values near 4.5, 3.6 and 2.0 characteristic of an S = 3/2 metal-containing centre. The N-methylformamide extracts activated the MoFe protein polypeptides from mutants of nitrogen-fixing bacteria unable to synthesize FeMoco, the active centre of Mo-nitrogenase. The active hybrid protein exhibited the characteristic substrate-reducing phenotype associated with the VFe protein except that it could not reduce N2 to NH3. The above data are interpreted as demonstrating the existence of an iron- and vanadium-containing cofactor, FeVaco, within the VFe protein. It is suggested that nitrogen fixation requires specific interactions between FeVaco or FeMoco and their respective polypeptides. The biosynthesis of these cofactors is discussed. 相似文献
6.
An amide conjugate of o-methoxybenzoic acid and aspartic acid has been isolated from bean leaves. After extraction and methylation of plant material, this compound was isolated as two isomeric monoethyl monomethyl esters. The ethylation of the aspartyl carboxyl groups was shown to be a likely result of an extraction procedure utilising acidified ethanol, the methylation of the aromatic hydroxy of the methoxy group to be due to the derivatisation procedure. Studies with pentafluorobenzylation confirmed that the endogenous compound is o-hydroxybenzoylaspartate. 相似文献
7.
Six embalmed human cadaveric hemi-pelves with their associated proximal femurs have been tested in vitro using 25 strain-gauge rosettes on each hemi-pelvis. Loads were applied up to 2.5 kN and principal stresses were computed from the principal strain data. Acetabular prostheses, cemented in place upon a cartilage-devoid but intact subchondral bone-plate, showed little change in stress-patterns when compared with the normal data, regardless of whether or not the component employed metal-backing. The use of 30 anchoring holes of 6.4 mm diameter, in the intact subchondral bone-plate, had little effect upon the stress-patterns, regardless of whether metal-backing was employed upon the prosthesis. When the subchondral bone-plate was removed, there were notable changes in the stress-pattern in the periacetabular region and on the medial wall of pelvis. The metal-backed prosthesis did not produce such notable changes as its plastic counterpart, when the subchondral bone-plate was removed. The use of a plastic prosthesis cemented in a Protrusio ring, in an acetabulum devoid of subchondral bone, produced notable changes in the stress-patterns in the whole periacetabular region and on the medial wall. 相似文献
8.
The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA 总被引:1,自引:0,他引:1
Base ratios and total DNA amounts can vary substantially between and within
higher taxa and genera, and even within species. Gene conversion is one of
several mechanisms that could cause such changes. For base substitutions,
disparity in conversion direction is accompanied by an equivalent disparity
in base ratio at the heterozygous site. Disparity in the direction of gene
conversion at meiosis is common and can be extreme. For transitions (which
give purine [R]/pyrimidine [Y] mispairs) and for transversions giving
unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow
but systematic changes in G + C percentage. For transversions giving like
R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the
extent of correction direction disparity, one can deduce properties of
repair enzymes, such as the ability (1) to excise preferentially the purine
from one mispair and the pyrimidine from the other for two different R/Y
mispairs from a single heterozygous site and (2) to excise one base
preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show
strong disparity in conversion direction, with preferential cutting of the
nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA.
The opposite directions of disparity for frame-shifts and their intragenic
suppressors as Ascobolus suggest that repair enzymes have a strong,
systematic bias as to which strand is cut. The conversion spectra of
mutations induced with different mutagens suggest that the nonlooped strand
is preferentially cut, so that base additions generally convert to mutant
and deletions generally convert to wild-type forms. Especially in
nonfunctional or noncoding DNA, this could cause a general increase in DNA
amounts. Conversion disparity, selection, mutation, and other processes
interact, affecting rates of change in base ratios and total DNA.
相似文献
9.
I.H.J. Bourne 《Journal of theoretical biology》1984,110(4):541-557
The hypothesis considers the anatomy and physiology of the memory-storing neuron from the viewpoint that an eccentrically placed nucleus with a Golgi Apparatus situated between it and the proximate cell membrane could be the mechanism for the storage and retrieval of experience and thought processes. Metabolites which enter the Golgi Apparatus are filtered and refined before being discharged from the surface which faces the cell membrane. They travel by the shortest route to a special location on the nearest part of the cell membrane. At this "favoured spot" the action potential is reactivated before the metabolites reach other parts of the membrane. Afferent impulses arriving via the synapses at the "favoured spot" and its tributary dendrites have priority controls the specific polarity of the cell, enabling it to record, store and reproduce the memory of its initial stimulus. Reinforcing stimuli cause the eccentric nucleus and Golgi Apparatus to move nearer to the favoured spot. This mechanism could be the basis of memory. The hypothesis may be applied to other observed phenomenon of brain function and might be submitted to experiment confirmation. 相似文献
10.
Amino acid sequence of retinal transducin at the site ADP-ribosylated by cholera toxin 总被引:31,自引:0,他引:31
C Van Dop M Tsubokawa H R Bourne J Ramachandran 《The Journal of biological chemistry》1984,259(2):696-698
Transducin was [32P]ADP-ribosylated by cholera toxin in bovine retinal rod outer segments and then partially purified on omega-amino octyl agarose to remove other ADP-ribosylated proteins. Trypsin digestion of the ADP-ribosylated transducin and further purification using boronate-polyacrylamide beads and high performance liquid chromatography yielded a single radiolabeled tetrapeptide, Ser-Arg-Val-Lys. The ADP-ribose is linked to the guanidinium group of arginine. 相似文献