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C Carr

Publications and source records attributed to C Carr.

At least 37 records · Page 2Linked to original sources
PubMed1987

The 43-kilodalton protein of Torpedo nicotinic postsynaptic membranes: purification and determination of primary structure.

The primary structure of the 43-kilodalton peripheral membrane protein (43-kDa protein) of Torpedo nicotinic postsynaptic membrane has been determined. The 43-kDa protein, which was isolated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, has an amino terminus resistant to Edman degradation, while the sequence at the carboxyl terminus is Tyr-Val. An amino acid sequence of 405 residues was obtained by NH2-terminal sequence analysis of complementary peptides generated by digestion with trypsin, chymotrypsin, Staphylococcus aureus V8 protease, and endoproteinase Lys-C, as well as by chemical cleavage at methionine. This sequence of molecular mass 45,618 daltons lacks the amino terminus but extends to the carboxyl terminus of the 43-kDa protein. Unusual structural features of the 43-kDa protein include two regions of approximately 80 residues, each containing 10% cysteine, as well as stretches predicted to exist as amphipathic alpha-helices. Other than the group blocking the amino terminus, no evidence was found for posttranslational modification of amino acids. The 43-kDa protein may represent a novel protein family because a computer search of this sequence with the National Biomedical Research Foundation data base (Release 12.0) did not reveal any significant homology to known protein sequences.

Amino Acid Sequence↗
PubMed1987

cDNAs for the postsynaptic 43-kDa protein of Torpedo electric organ encode two proteins with different carboxyl termini.

Postsynaptic membranes isolated from Torpedo electric organ are highly enriched in the nicotinic acetylcholine receptor and a nonreceptor protein of 43 kDa; the distribution of the 43-kDa protein and the receptor is coextensive in the electrical membrane. As a first step in understanding the regulation of 43-kDa protein expression, we have isolated and characterized 43-kDa protein cDNAs. A lambda gt11 cDNA library was constructed from Torpedo californica electric organ mRNA and screened with a pool of 26-mer oligonucleotides encoding a short tryptic fragment of the 43-kDa synaptic protein. Positive clones were purified and sequenced; the amino acid sequences were deduced, and they matched chemically determined protein sequences of the 43-kDa protein. Two distinct classes of cDNAs were obtained; one class encoded a 43-kDa protein of 389 amino acids with a calculated molecular mass of 43,988 daltons, and another class encoded a second 43-kDa protein containing 23 additional amino acids at the C terminus. Therefore, it appears that two 43-kDa proteins with different carboxyl termini are encoded by separate mRNAs. Consistent with this idea, blot hybridization analysis revealed multiple polyadenylylated 43-kDa mRNAs in electric organ. One polyadenylylated mRNA of approximately equal to 2.0 kilobases in length was apparent in both embryonic day-11 chick muscle and the mouse muscle cell line BC3H1.

Amino Acid Sequence↗
PubMed1987

Visualization of the cytoplasmic surface of Torpedo postsynaptic membranes by freeze-etch and immunoelectron microscopy.

The synapse-specific Mr 43,000 protein (43K protein) and the acetylcholine receptor were visualized by freeze-etch immunoelectron microscopy in preparations of purified Torpedo postsynaptic membranes. Vesicles were immobilized on glass and then sheared open by sonication to expose the cytoplasmic surface. Membranes were labeled with monoclonal antibodies to the 43K protein or the acetylcholine receptor. The cytoplasmic surface was devoid of filamentous structure, and the 43K protein and the cytoplasmic projection of the acetylcholine receptor were associated with prominent surface particles. Acetylcholine receptor and 43K protein, in membrane surfaces in direct contact with glass coated with polyornithine, segregated into dense particle aggregates separated by smooth membrane patches, whereas those in contact with glass coated with Alcian Blue underwent little or no detectable rearrangement. After treatment of vesicles at alkaline pH to remove the 43K protein, the cytoplasmic surfaces were still covered by a dense array of particles that were more uniform in shape and appeared slightly shorter than those seen on unextracted membranes, but similar in height to the extracellular projection. Monoclonal antibodies to the acetylcholine receptor labeled these particles, while antibodies to 43K protein did not. We conclude that the 43K protein is in direct association with the receptor and that complexes of the receptor and 43K protein can undergo surface-induced lateral redistribution. In addition, the cytoplasmic projection of the acetylcholine receptor is sufficiently large to be readily detected by freeze-etch electron microscopy and is similar in height to the extracellular projection.

Animals↗
PubMed1985

Trichothecene structure and toxicity to the green alga Chlorella pyrenoidosa.

Using the paper-disk method with Chlorella-seeded agar plates, 15-acetoxyscirpenol, HT-2 toxin, acetyl T-2 toxin and neosolaniol inhibited growth at a concentration of 1 mg/ml, whereas verrucarol, T-2 tetraol, nivalenol, fusarenon-X, deoxynivalenol and 3-acetyldeoxynivalenol were inactive. Taking into account that verrucarin A, roridin A, T-2 toxin and diacetoxyscirpenol had previously been found to strongly inhibit Chlorella growth, esterification at R15 appears to be important for growth inhibitory activity. The most active agents are also esterified at R4. Inhibition of protein synthesis appears to be involved in the toxicity.

Chlorella↗
PubMed1985

Mechanism of polymyxin B-mediated lysis of lipopolysaccharide-treated erythrocytes.

A novel system was used previously to characterize the dynamic interaction of a polysaccharide-deficient, lipid-rich lipopolysaccharide (LPS) with rabbit erythrocytes (RaRBC). Exposure of the RaRBC to the LPS rendered them sensitive to induction of hemolysis by the cationic antibiotic polymyxin B (PB) in a time- and temperature-independent manner. Subsequent decay in the response of LPS-sensitized cells to PB was shown to be critically dependent on both the time and temperature of incubation of RaRBC with LPS and to be independent of a change in LPS binding (Carr and Morrison, Infect. Immun. 43:600-606, 1984). In the present study, we performed experiments designed to define the mechanism by which PB mediates hemolysis of LPS-sensitized RaRBC. Experiments were performed to examine the molecular requirements of the LPS and the PB that were essential for hemolytic activity. The capacity of various cations to mediate hemolysis of LPS-sensitized RaRBC or to block PB-mediated hemolysis and the temperature dependence of the PB lytic reaction were investigated. The results of these experiments suggest that PB-mediated hemolysis of LPS-treated erythrocytes is dependent upon an initial ionic association of PB with erythrocyte membrane-bound LPS, followed by hydrophobic insertion of the PB fatty acid into the erythrocyte membrane lipid bilayer.

Animals↗
PubMed1984

Lipopolysaccharide interaction with rabbit erythrocyte membranes.

In this study we have characterized the association of a polysaccharide-deficient, lipid-rich lipopolysaccharide (LPS) with rabbit erythrocytes (RaRBC). With polymyxin B sulfate-mediated hemolysis as a probe, we have shown that Salmonella minnesota R595 LPS interacts with RaRBC in two distinguishable steps. The first step whereby RaRBC exposed to LPS are rendered sensitive to polymyxin B-initiated lysis probably represents absorption of LPS to the RaRBC membrane. We investigated two possible mechanisms for the subsequent time-dependent decrease in response of LPS-treated RaRBC to polymyxin B. We found that the decay in polymyxin B susceptibility of LPS-treated RaRBC cannot be attributed to a decrease in binding of LPS to the RaRBC. On the other hand, our results are consistent with a time-dependent rearrangement of the amphipathic LPS within the lipid bilayer of the RaRBC membrane. In particular, at lower incubation temperatures of RaRBC and LPS, the decay in polymyxin B-induced hemolysis is slower, presumably, because the increased membrane viscosity allows less rapid rearrangement of LPS within the lipid bilayer. A putative hydrophobic intercalation of LPS into a mammalian cell membrane may be of importance in LPS stimulation of responsive cells.

Absorption↗
PubMed1982

The pathophysiology of compression injuries of the peripheral facial nerve.

The buccolabial branches of guniea pig facial nerves were crushed to produce axonotmesis, Wallerian degeneration, and demyelination. The lesions were followed from 1 to 8 weeks by transmission electron microscopy, electrophysiological tests, and cytochemical staining methods for Na+ channels. The first week demonstrated the classic degenerative neural changes. At 2 weeks the axoplasmic side of the demyelinated axolemma demonstrated diffuse staining for Na+ channels at a distance of 1 micrometer. At 4 weeks multiple condensed areas of dense staining were noted along the demyelinated axolemma. These staining areas resemble in character and length a normal node of Ranvier and denote new Na+ channels. The internodal distance is shorter than for the normal facial nerve. At 6 weeks a thin layer of myelin covered the nerve fibers. At 8 weeks half of the nerves were normal sized and the myelin sheath was normal in width. Following nerve crushing, electrical activity is present for 24-48 hours in the axonotmetic distal stump. Then the axon becomes unresponsive to electrical stimulation. There is gradual resumption of electrical activity between 5 and 14 days. Normal conduction resumes by 8 weeks. This study provides ultrastructural and cytochemical evidence for nerve fiber reorganization, axolemmal plasticity and sodium channel production and redistribution following Wallerian degeneration and demyelination in axonotmesis. Resumption of electrical neural excitability is achieved by an increase in the density of sodium channels and reduction in the internodal distance as a means for impedence matching. Reduction of the cross sectional diameter of the regenerating axon facilitates electrical conduction.

Animals↗
PubMed1981

Input to the medullary pacemaker nucleus in the weakly electric fish, Eigenmannia (sternopygidae, gymnotiformes).

In order to identify which brain centers are involved in the control of electric organ discharge in electric fish, HRP was injected into the medullary electromotor (pacemaker) nucleus in the gymnotoid Eigenmannia. Neurons were retrogradely labeled in only a small nucleus of the mesencephalic tegmentum, herein called the prepacemaker nucleus. The prepacemaker nucleus lies just caudal and ventral to the posterior commissure and comprises at least two types of neurons.

Afferent Pathways↗
PubMed1980

Later stages of development of the periotic duct and its adjacent area in the human fetus.

The later stages of development (16-40 weeks in utero) of the periotic duct and its adjacent areas in the human fetus indicate that the critical stages of development occur in four specific time related stages over a six-week period (20-26 weeks). First, the petrous apex ossifies to separate th inferior cochlear vein into the canal of Cotugno and forms the medial wall of the cochlear aqueduct (22 weeks); second, the canalicular otic capsule fuses with the cochlear otic capsule to obliterate Hyrtl fissure and forms of the lateral wall of the cochlear aqueduct (24 weeks); third, progressive bone deposition to the medial surface of the membranous labyrinth and cochlea at the petrous apex elongates the periotic duct and cochlear aqueduct (32 weeks in utero); and fourth, active arachnoid tissue ingrowth into the periotic duct occurs at 20-24 weeks and 34-40 weeks in utero. The terminal event is widening of the CNS opening of the periotic duct at 32 weeks in utero. The periotic duct and cochlear aqueduct length increase with gestation from 25 weeks until term. The periotic duct width remains the same throughout the gestation. The cochlear aqueduct width diminishes with gestational age. The periotic duct remains patent throughout 16-40 weeks in utero.

Cochlea↗
PubMed1979

The ultrastructural cytochemistry of peroxisomes in the guinea pig cochlea: a metabolic hypothesis for the stria vascularis.

The roles of catalase and alpha-hydroxyacid oxidase activities are studied in the peroxisomes of the guinea pig inner ear. The major activities are located primarily in the intermediate cells of the stria vascularis. The peroxisomes of the stria vascularis behave cytochemically in a similar fashion to those found in the proximal convoluted tubules of the kidney. This study indicates that the stria vascularis may behave as a compartmentalized metabolic system.

Alcohol Oxidoreductases↗
PubMed1978

Distribution of the crossed olivocochlear bundle in the chinchilla's cochlea.

The efferent crossed olivocochlear bundle (COCB) was transected in the brain stem of the chinchilla, and the animals sacrificed 7 to 96 days later. Electron microscopy revealed that all the large efferent nerve endings on outer hair cells in the basalmost 2 mm (round window region) of the cochlea had degenerated, 87.5% in the remainder of the first turn, 70% in the second turn and 43% in the third turn. Only a few degenerating nerve fibers were seen in the medial spiral tract (inner spiral and tunnel bundles) of the experimental animals. Nerve fibers were counted in the medial spiral tracts of the cochleas of control animals as well as in those animals whose COCB had been transected. There were considerable individual variations in the fiber numbers, and statistical analysis showed no significant difference between the numbers of nerve fibers in normal and experimental animals. The cochlear microphonics (CM) and nerve action potentials (AP) of acute animals were assessed before and after COCB section. The CM and AP of the chronic experimental animals were compared with responses from normals. Overall, no changes in a physiological response of the anesthetized chinchilla could be attributed to complete section of the COCB.

Acetylcholinesterase↗