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C Robinson

Publications and source records attributed to C Robinson.

At least 181 records · Page 10Linked to original sources
PubMed1995

A SecY homolog in Arabidopsis thaliana. Sequence of a full-length cDNA clone and import of the precursor protein into chloroplasts.

Proteins are translocated across the thylakoid membrane by two distinct pathways in higher plant chloroplasts, one of which is related to prokaryotic Sec-dependent translocation mechanisms. SecY is an essential, hydrophobic component of the membrane-bound translocase complex in bacteria, and we report here the nucleotide sequence of a full-length cDNA encoding a homolog of SecY from Arabidopsis thaliana. The predicted protein of 551 residues includes an amino-terminal extension of approximately 120 residues when compared with other SecY proteins. The deduced sequence of the mature protein, cpSecY, is 41% identical with SecY from Synechococcus and 33% identical with the Escherichia coli protein. The extension serves to target the protein into chloroplasts; transcription-translation of the cDNA yields a 58-kDa precursor protein which is imported into pea chloroplasts, processed to a product of 46 kDa, and targeted into the thylakoid membrane.

Amino Acid Sequence↗
PubMed1995

Evidence for SecA- and delta pH-independent insertion of D1 into thylakoids.

Many nuclear-encoded proteins are targeted into chloroplast thylakoids by an azide sensitive Sec-related mechanism or by a delta pH-driven mechanism. In this report, the requirements for the integration of chloroplast-encoded thylakoid proteins have been analysed in pulse-labeled intact chloroplasts. We show that the integration of the photosystem II reaction centre protein, D1, continues in the absence of a delta pH and in the presence of azide. A range of other proteins are similarly targeted to thylakoids in the presence of azide, suggesting that the SecA-related mechanism is not widely used for the targeting of chloroplast-encoded proteins.

Adenosine Triphosphatases↗
PubMed1995

A new type of signal peptide: central role of a twin-arginine motif in transfer signals for the delta pH-dependent thylakoidal protein translocase.

The delta pH-driven and Sec-related thylakoidal protein translocases recognise distinct types of thylakoid transfer signal, yet all transfer signals resemble bacterial signal peptides in structural terms. Comparison of known transfer signals reveals a single concrete difference: signals for the delta pH-dependent system contain a common twin-arginine motif immediately before the hydrophobic region. We show that this motif is critical for the delta pH-driven translocation process; substitution of the arg-arg by gln-gln or even arg-lys totally blocks translocation across the thylakoid membrane, and replacement by lys-arg reduces the rate of translocation by > 100-fold. The targeting information in this type of signal thus differs fundamentally from that of bacterial signal peptides, where the required positive charge can be supplied by any basic amino acid. Insertion of a twin-arg motif into a Sec-dependent substrate does not alter the pathway followed but reduces translocation efficiency, suggesting that the motif may also repel the Sec-type system. Other information must help to specify the choice of translocation mechanism, but this information is unlikely to reside in the hydrophobic region because substitution by a hydrophobic section from an integral membrane protein does not affect the translocation pathway.

Amino Acid Sequence↗
PubMed1995

The delta pH-driven, ATP-independent protein translocation mechanism in the chloroplast thylakoid membrane. Kinetics and energetics.

Previous studies have shown that proteins are transported across the chloroplast thylakoid membrane by two very different mechanisms, one of which requires stromal factors and ATP, whereas the other mechanism is ATP independent but completely reliant on the thylakoidal delta pH. We have examined the role of the delta pH in the latter mechanism by simultaneously monitoring the magnitude of delta pH (by 9-aminoacridine fluorescence quenching) and the rate of import of the 23-kDa photosystem II protein into isolated pea thylakoids. We show that protein import can take place, at low but significant rates, at very low values of delta pH (in the region of 1.2-1.4), and that plots of the rate of protein import against proton concentration gradient are probably hyperbolic in nature. There is no evidence for a threshold level of delta pH which is required to drive translocation of the 23-kDa protein. Addition of uncouplers midway during import incubations results in a rapid and complete inhibition of translocation, showing that the continuous presence of the delta pH is required for translocation to take place. During import into intact chloroplasts, the intermediate-size 23-kDa protein substrate for the thylakoidal protein transport machinery is found only in the stromal fraction at all values of delta pH, suggesting that the initial interaction with the machinery is relatively weak, reversible and delta pH-independent. We therefore propose that the delta pH is required for both the initiation and completion of translocation; these roles are in marked contrast to the roles of protonmotive force in mitochondrial and sec-dependent bacterial protein transport.

Adenosine Triphosphate↗
PubMed1995

A monomeric, tightly folded stromal intermediate on the delta pH-dependent thylakoidal protein transport pathway.

Two distinct mechanisms have been previously identified for the transport of proteins across the chloroplast thylakoid membrane, one of which is unusual in that neither soluble factors nor ATP are required; the system requires only the transthylakoidal delta pH. We have examined this mechanism by studying the properties of one of its substrates: the extrinsic 23-kDa protein (23K) of photosystem II. Previous work has shown that this protein can be transported into isolated thylakoids as the full-length precursor protein; we show that the stromal import intermediate form of this protein is similarly translocation-competent. Gel filtration tests indicate that the stromal intermediate is probably monomeric. Protease sensitivity tests on both the initial in vitro translation product and the stromal import intermediate show that the presequence is highly susceptible to digestion whereas the mature protein is resistant to high concentrations of trypsin. The mature protein becomes very sensitive to digestion if unfolded in urea, or after heating, and we therefore propose that the natural substrate for this translocation system consists of a relatively unfolded presequence together with a tightly folded passenger protein. The ability of thylakoids to import pre-23K is destroyed by prior treatment of the thylakoids with low concentrations of trypsin, demonstrating the involvement of surface-exposed proteins in the import process. However, we can find no evidence for the binding of pre-23K or i23K to the thylakoid surface, and we therefore propose that the initial interaction of these substrates with the thylakoidal translocase is weak, reversible, and probably delta pH-independent. In the second phase of the translocation mechanism, the delta pH drives either the translocation and unfolding of proteins, or the translocation of a fully folded protein.

Bacterial Proteins↗
PubMed1995

Assessment of mortality in the construction industry in the United States, 1984-1986.

Construction, one of the larger industries in the United States, employs 7.6 million workers, many in skilled trades occupations. Previously published data about potential worksite exposures and mortality of construction site workers are limited. We analyzed occupation and industry codes on death certificates from 19 U.S. states to evaluate mortality risks among men and women usually employed in construction occupations. Proportionate mortality ratios (PMRs) for cancer and several other chronic diseases were significantly elevated among 61,682 white male construction workers who died between 1984 and 1986. Men younger than age 65, who were probably still employed immediately prior to death, had significantly elevated PMRs for cancer, asbestos-related diseases, mental disorders, alcohol-related disease, digestive diseases, falls, poisonings, traumatic fatalities that are usually work-related, and homicides. Elevated PMRs for many of the same causes were observed to a lesser degree for black men and white women whose usual industry was construction. In addition, women experienced excess cancer of the connective tissue and suicide mortality. Various skilled construction trades had elevated PMRs for specific sites, such as bone cancer and melanoma in brickmasons, stomach cancer in roofers and brickmasons, kidney and bone cancer in concrete/terrazzo finishers, nasal cancer in plumbers, pulmonary tuberculosis in laborers, scrotal cancer and aplastic anemia in electricians, acute myeloid leukemia in boilermakers, rectal cancer and multiple sclerosis in electrical power installers, and lung cancer in structural metal workers. Using a standard population of blue collar workers did not result in fewer elevated PMRs for construction workers. Despite lifestyle differences and other limitations of the study, the large numbers of excess deaths observed in this study indicate the need for preventive action for construction workers.

Accidents, Occupational↗
PubMed1995

Effect of stopping fluoride administration on the distribution profiles of fluoride in three different kinds of rat bones.

The aim of this work was to explore the reduction of fluoride concentrations in the skeleton after stopping experimental fluoride administration. Fluoride was administered to the rats at varying doses (0, 50, 100 ppm in drinking water) and for different lengths of time (4, 13, 25 weeks). A series of fluoride concentrations across the full thickness of humerus, parietal bone, and vertebra arch in rats were measured by means of an abrasive micro-sampling technique. The distribution profiles of fluoride from periosteal to endosteal surfaces, which were apparently related to the histological structure of these bones, were U shaped in the humerus, V shaped in the parietal bone, and W shaped in the vertebra arch. The average fluoride concentrations in the bones increased significantly with each increasing dose and length of fluoride administration. The relative increments were similar between the different regions or the different bones. After stopping fluoride administration, on the other hand, the relative reduction of the average fluoride concentrations in the bones were 30-100%. They were greatly related to the length after stopping fluoride administration and the dose and length of fluoride administration, but also dependent upon the type of bone and the region examined.

Animals↗
PubMed1995

Identification of nonlinear model of ankle joint dynamics during electrical stimulation of soleus.

The mechanical impedance of the ankle joint was estimated in two conditions: during submaximal surface electrical stimulation of the soleus muscle, and with no stimulation applied. Both neurologically intact (n = 5) and spinal cord injured subjects (n = 4) were used. The mechanical impedance was measured by applying angular step and constant velocity (13-100 degrees s-1) perturbations at 10 degrees to the ankle and measuring the resulting changes in torque. A five-element lumped model consisting of an inertial element, a parallel elastic element, and an elastic element in series with a viscous element and a pure tension generator produced a good fit for predicting the compliance characteristics of the ankle for both the relaxed and stimulated conditions. The elastic elements were piecewise linear with different values for the dorsiflexion and plantarflexion directions. The viscous element was velocity-dependent and it decreased in value as the velocity increased. The average torque error between the measured and model's response during soleus stimulation was 10.56% for the dorsiflexed and 11.93% for the plantarflexed perturbations. However, the average error was skewed by several subjects who had excessive error, due to volitional intervention or flexor withdrawal reflex. The average model error for the perturbations without stimulation was 7.12% for dorsiflexed and 5.58% for plantarflexed perturbations.

Ankle Joint↗
PubMed1995

Psychosocial correlates of immune responsiveness and illness episodes in US Air Force Academy cadets undergoing basic cadet training.

This study examined psychosocial correlates of immune function and illness in 89 male first-year US Air Force Academy cadets. A psychosocial questionnaire was administered to cadets prior to their arrival at the academy and was readministered during cadet orientation and during the stressful environment of Basic Cadet Training (BCT). Immune responsiveness was analyzed by PHA-, PMA-, or anti-CD3-stimulated thymidine uptake in mononuclear leucocytes. Illness episodes were assessed via medical chart review and self-reported symptoms. There were significant increases in distress levels as cadets entered BCT. No psychosocial measure assessed prior to arrival at the academy predicted level of PHA-, PMA-, and anti-CD3-stimulated thymidine uptake or risk of illness. However, hostility levels reported during BCT predicted risk of illness in the four weeks following psychosocial assessment (odds ratio = 7.1; 95% confidence interval: 1.4-36.1). Elevated response to environmental stressors and lower well-being levels also predicted impending illness, but only in the cohort of cadets who had not contracted food poisoning prior to assessment during BCT (OR = 9.3, CI = 1.9-46.7; OR = 0.09, CI = 0.02-0.53). These results suggest that self-report measures of hostility, response to environmental stressors and well-being may be useful predictors of impending illness episodes in males encountering high stress environments.

Adaptation, Psychological↗
PubMed1995

Axillary sampling and radiotherapy does not compromise the patient with early breast cancer: Trafford database experience.

Local recurrence has been studied in a selected group of 379 patients, 39% of whom underwent simple mastectomy and 61% lumpectomy. The axilla was sampled in 52%, cleared in 8% and untreated in 40%. Axillary recurrence occurred in 16% of patients with a median follow-up of 54 months. Ninety-one per cent of these patients with lymph node recurrence had no surgery or sampling to the axilla, and a third received radiotherapy. Local recurrence was satisfactorily controlled by various modalities of treatment in all but 29 patients. Death related to distant metastasis in all but six of these 29 patients. Analysis suggests that patients with locally uncontrolled disease had aggressive tumours at diagnosis which were larger than average, most often grade 3 histologically and more frequently required mastectomy. Our results support previous studies indicating that survival would not be influenced by more radical surgery but that sampling followed by radiotherapy would have prevented the majority of our lymph node recurrences.

Adult↗
PubMed1995

A cost analysis of a case management system for infants with chronic illnesses and developmental disabilities.

Service coordination has long been a documented need of children with disabilities. The purpose of this study was to examine the costs associated with providing a comprehensive system of service coordination for hospitalized infants and toddlers with special health care needs and their families. Coordination costs were evaluated across seven functions including (a) determining eligibility for services, (b) identifying and arranging evaluations, (c) providing support to families, (d) making referrals to outside agencies, (e) exchanging information among service providers and families, (f) maintaining follow-up contact, and (g) determining discharge from the program. Results indicated that the service coordination function of providing family support was the most time-consuming task area, followed by the functions of exchanging information and maintaining follow-up contact. Costs also varied with the medical diagnosis and the child's age. Consistent with this variability, the diagnostic category and/or possibly the length of hospitalization was a better correlate of total cost of service coordination per child than was the number of months served. The complexity of the family's social and financial situation also appeared to be related to cost per month of service.

Case Management↗
PubMed1995

In vitro and in vivo analysis of murine lipoprotein lipase gene promoter: tissue-specific expression.

Lipoprotein lipase, an enzyme of central importance to lipid metabolism, is most abundant in adipose tissues, cardiac and skeletal muscle, and portions of the brain. The current work examined the murine lipoprotein lipase promoter using transient transfection, gel-retention analyses, and transgenic mice. Maximum expression of the luciferase reporter gene in transfected cells was observed with -101 bp of the promoter. Nuclear extracts from tissues expressing lipoprotein lipase contained DNA binding proteins that recognize the CCAAT box (-64 bp) and an octamer motif (-46 bp); this combination of factors was absent in nonexpressing tissues. Transgenic mice from three of five founders prepared with -1,824-bp promoter constructs expressed the luciferase reporter gene at highest levels in brown adipose tissue and brain. These findings suggest that the -1,824-bp promoter region contains sequence elements responsible for the tissue-specific transcription of lipoprotein lipase in vivo.

Animals↗
PubMed1995

Fluoride distribution of rat molar cementum in relation to age and fluoride levels in the drinking water.

The present study was undertaken to determine the fluoride distribution profile in rat molar cementum with age in relation to fluoride in drinking water. Fifty-four female Wistar rats were used for the experiment. Before the experiment 6 rats were killed under chloroform anesthesia at 4 weeks of age as controls. The remaining 48 rats were divided into two groups: a control group given distilled water and the other group given water containing 100 ppm fluoride ad libitum. Six rats from each group were killed at the ages of 6, 12, 24, and 48 weeks. The fluoride distribution in the molar cementum was analyzed from the surface to the cementodentinal junction by abrasive microsampling. The fluoride concentrations in molar cementum from control rats on distilled water remained relatively constant until 24 weeks. A small increase then occurred between 24 and 48 weeks. The fluoride concentration in cementum from rats drinking water containing 100 ppm fluoride increased markedly with age, both in outer and inner regions of the molar cementum for all rats. On the other hand, the fluoride concentration in the cementum of older rats drinking water with 100 ppm fluoride was significantly higher in the outer than in the inner region of the cementum. It was concluded that the fluoride distribution in rat molar cementum may increase throughout life in relation to the fluoride level in the drinking water.

Age Factors↗
PubMed1995

Augmentation of permeability in the bronchial epithelium by the house dust mite allergen Der p1.

Sequence analyses have revealed the existence of homology between certain aeroallergens and proteolytic enzymes. This homology can be expressed functionally, but its significance to airway pathophysiology is unknown. Studies with Madin-Darby canine kidney cells and canine tracheal epithelial cells grown on plastic substrata or matrix proteins suggest that Der p1, a major allergen from the house dust mite Dermatophagoides pteronyssinus and a cysteine proteinase, or the unfractionated growth medium extract (SGME) from which it was purified, are both capable of causing cell detachment. The ability of both agents to produce functional changes in the barrier function of the epithelium was further demonstrated using isolated bovine airway preparations. Over a 3-h duration, both Der p1 and SGME elicited significant increases in the permeability of isolated sheets of bronchial mucosa to serum albumin. Exposure of isolated bronchial segments to luminally applied solutions of Der p1 resulted in histologic evidence of epithelial injury. Neither Der p1 nor SGME was active in these experimental systems unless chemically reduced, suggesting that the effect was initiated by cysteine proteinase activity. Similar augmentation of mucosal permeability and tissue injury was produced by bovine trypsin and collagenase from Clostridium histolyticum. In both the isolated mucosal sheet model and in cultured cells, the actions of Der p1 or SGME were associated with relatively little cytolysis, suggesting a specific action of the reagents on cell attachment. These results demonstrate a new functional activity of Der p1 that may be germane to the processes of allergen presentation, inflammatory cell activation, and chronic tissue injury.

Animals↗
PubMed1995

The effect of glycosylaminoglycans on the mineralization of sheep periodontal ligament in vitro.

The effect of removal of glycosylaminoglycans on the mineralization of sheep periodontal ligament was determined using enzyme digests followed by incubation in solutions supersaturated with respect to hydroxyapatite at pH 7.4. TEM revealed that control periodontal ligament remained unmineralized. However, tissue from which glycosylaminoglycans had been removed contained plate-like crystals arranged parallel to and within the collagen fibrils. Electron probe and electron diffraction studies suggested that the crystals were apatitic with a similar order of crystallinity to dentine, and a Ca:P ratio of 1.61. In addition, the glycosylaminoglycan content of periodontal ligament, cementum and alveolar bone was compared using cellulose acetate electrophoresis. Periodontal ligament contained predominantly dermatan sulfate while cementum and alveolar bone contained mostly chondroitin sulfate. A role for glycosylaminoglycans in maintaining the unmineralized state of the periodontal ligament is suggested. Control of expression of specific proteoglycan species on a spatially restricted basis is presumably central to this role.

Alveolar Process↗
PubMed1995

The control of ingress of albumin into developing enamel from adjacent dentine of the rat incisor.

The present study used an immunohistochemical approach to map the distribution of albumin within the dentine adjacent to the developing enamel of both impeded and unimpeded rat incisors to determine if the dentine could be a possible route of entry for this protein into the developing enamel matrix. In dentine adjacent to the secretory and transition stages of the developing enamel, the dentinal tubules were labelled only over approximately the pulpal quarter of their length. The bulk of the dentine showed no labelling. However, labelling within the dentine appeared at the ADJ at a position approximately 2.5 mm occlusal to the distal root of the first molar, adjacent to enamel with no visible residual matrix. The results of this study suggest that adventitious ingress of albumin into enamel from the dentine is restricted during enamel secretion and can only potentially occur once enamel maturation has been initiated.

Albumins↗