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Biomedical subjects

C Robinson

Publications and source records attributed to C Robinson.

At least 235 records · Page 13Linked to original sources
PubMed1993

The stromal processing peptidase activities from Chlamydomonas reinhardtii and Pisum sativum: unexpected similarities in reaction specificity.

We have partially purified the stromal processing peptidase from Chlamydomonas reinhardtii and compared the properties of this activity with those of the pea counterpart. Whereas previous studies have suggested that the two enzymes may have significantly different reaction specificities, we find that they are in fact very similar. Both enzymes process precursors of two higher-plant thylakoid lumen proteins, and one C. reinhardtii lumenal protein, to similar intermediate-size forms. However, whereas the algal enzyme processes the precursor of C. reinhardtii Rubisco small subunit to the correct mature size, this precursor is cleaved only to an intermediate size by the pea enzyme. The small subunit precursor from pea appears to be cleaved by both enzymes in a similar manner. In terms of sensitivity to inhibitors, the two activities are notably different; the pea enzyme has previously been shown to be inhibited by several types of heavy-metal chelator, but we have found that none of these compounds affect the algal activity.

Animals↗
PubMed1993

The effect of rate of eruption on periodontal ligament glycosylaminoglycan content and enamel formation in the rat incisor.

The rate of eruption of rat mandibular incisors was either increased by cutting one tooth out of occlusion or eliminated by means of pinning. The effects of such changes in eruption rate on the sulphated glycosylaminoglycan content of the periodontal ligaments was analysed. The length of the enamel secretory zone and the composition of the developing enamel matrix protein was also compared. Sulphated glycosylaminoglycan content of the periodontal ligament increased fourfold (P < 0.001) during accelerated eruption but decreased to a corresponding extent (P < 0.001) in the absence of eruption, when compared with controls. The length of the enamel secretory zone was also significantly reduced in the immobilised teeth, although the protein content was similar compared with controls. The results demonstrate the differential response to varied eruption rates of the periodontal ligament and enamel, particularly in respect of the extracellular matrix. The data are consistent with the view that the ground substance of the periodontal ligament plays a role in the generation of the eruptive force.

Amelogenin↗
PubMed1993

An immunohistochemical study of the effects of fluoride on enamel development in the rat incisor.

A monoclonal antiamelogenin antibody was used to investigate the effects of fluoride on enamel development in the rat incisor. The results suggested that during secretion the enamel matrix molecules are arranged in such a way as to mask the epitope recognized by the monoclonal antibody. However, during the transition stage of development as the matrix begins to be degraded the epitope becomes exposed and labelling intensity increases to reach a maximum at the end of transition/start of maturation. The effect of fluoride is to delay the appearance of labelling within the enamel matrix until the end of transition. This suggests that the fluoride may inhibit enzymatic degradation or disaggregation of the matrix, the resulting residual matrix then inhibiting crystal growth.

Ameloblasts↗
PubMed1993

Fluoride uptake in human dentine from glass-ionomer cement in vivo.

The purpose was to examine F uptake and distribution in dentine from a F-containing glass-ionomer cement in vivo. Nine volunteers were selected from dental students who were scheduled for extraction of their third molars. Two cavities were prepared on the same occlusal surface of the third molars for each subject; one was restored with glass-ionomer cement (Virtabond), the other with zinc phosphate cement as a control. After 3 months the teeth were extracted. F profiles in the dentine from the cavity floor to the pulpal surface were determined in tissue immediately adjacent to the restorations. An abrasive micro-sampling technique was used. The F concentration of the dentine was highest immediately beneath glass-ionomer cement filling, decreasing towards the pulpal surface. Overall F concentrations were greater in the dentine beneath the glass-ionomer cement than in that beneath the zinc phosphate cement. It was concluded that the glass-ionomer cement markedly enhanced fluoride uptake by underlying dentine in vivo.

Adult↗
PubMed1993

Glucose clearance from different surfaces of human central incisors and first molars.

The study examined the glucose clearance (retention) in saliva at different surfaces of these teeth in 23 subjects. The mouth was thoroughly rinsed for 15 s with 20 ml of a 0.5 M glucose solution. The concentrations of glucose absorbed by small pieces of paper, placed on the mesial, distal, labial (buccal), lingual and occlusal surfaces 3 min after rinsing, were measured using an immobilized enzyme system and an electrochemical sensor. On the maxillary and mandibular central incisors, the glucose concentrations on the labial surfaces were significantly higher than on all other surfaces and lowest on the lingual surfaces. In the mandibular molars, glucose concentrations were significantly higher on the buccal surfaces than on the lingual surfaces. Clear site-specific differences in glucose clearance were thus observed at the different tooth surfaces. It is considered that the differences in the glucose retention rate might be indicative of factors important for the site specificity of dental caries.

Adult↗
PubMed1993

Enamel ultrastructure and protein content in X-linked amelogenesis imperfecta.

X-linked amelogenesis imperfecta has been proven in a number of families to be linked to or involve a variety of mutations in the X chromosome amelogenin gene. The purpose of this study was to characterize the enamel ultrastructure and enamel protein in a kindred affected by X-linked amelogenesis imperfecta. Exfoliated primary teeth were obtained from two related persons (one male, one female) who had X-linked amelogenesis imperfecta with marked hypoplasia. Normal enamel (age and sex matched) was used as the control for all analyses. The teeth were evaluated using light microscopy, scanning electron microscopy, and microradiography. The enamel of the heterozygous female was hypoplastic and rough with marked surface depressions. Enamel beneath these depressions was poorly organized and lacked a prismatic structure. The affected male had very thin enamel (approximately 40 microns) that also lacked an organized structure. Enamel protein from the teeth of the heterozygous female and the control was characterized using amino acid analysis. The protein content of the enamel of the female with amelogenesis imperfecta was 0.40% (N = 1) whereas the control enamel ranged from 0.17% to 0.45% (N = 4; mean = 0.34%). This study indicates that although the enamel in both the male and female with X-linked amelogenesis imperfecta displayed marked structural abnormalities the enamel protein was similar in quantity and amino acid composition for normal and X-linked amelogenesis imperfecta (female) enamel.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelogenesis Imperfecta↗
PubMed1993

A comparison of the effects of polyarginine and stimulated eosinophils on the responsiveness of the bovine isovolumic bronchial segment preparation.

1. The bovine isovolumic bronchial segment preparation has been used to study the sensitivity and responsiveness of bronchial smooth muscle after various manipulations. 2. Addition of acetylcholine (ACh) to the lumen of the segments elicited an increase in intraluminal pressure as a result of contraction of the airway smooth muscle. However, the increases in intraluminal pressure were greater when the ACh was added to the adventitial surface of the preparation. 3. Addition of polyarginine to the bronchial lumen for 60-120 min resulted in an increased magnitude of response and greater than 100 fold increase in sensitivity to ACh administered into the lumen. Depolarizations induced by KCl were similarly enhanced when the solution was added into the lumen. In contrast, the sensitivity and responsiveness to ACh or K(+)-induced depolarization administered adventitially was unchanged. 4. The mechanical disruption of the epithelium produced a 32 fold increase in sensitivity to ACh introduced via the lumen, whereas the sensitivity to ACh added adventitially remained unaltered. 5. Addition of polyarginine to the adventitial bathing medium resulted in no change in the responsiveness or sensitivity to ACh, irrespective of whether the ACh was given intraluminally or adventitially. 6. Histological examination revealed that polyarginine caused extensive disordering of the normal architecture of the bronchial epithelium. Taken together with the unaltered responsiveness to adventitial ACh (i.e. lack of change in intrinsic muscle sensitivity) these observations suggest that the effect of polyarginine was most likely due to disruption of a diffusion barrier. 7. In contrast to the effects of polyarginine, the only effect of stimulated eosinophils was to produce a small diminution in the responsiveness to ACh that had been added adventitially.

Acetylcholine↗
PubMed1993

Stimulated eosinophils and proteinases augment the transepithelial flux of albumin in bovine bronchial mucosa.

1. The apical to basolateral transmucosal flux of albumin has been measured in isolated sheets of bovine bronchial and tracheal mucosa. Under resting conditions the net unidirectional flux in the bronchial mucosa was not significantly different from that measured previously for the basolateral to apical vector. In contrast, the apical to basolateral flux in the tracheal mucosa was significantly lower than that measured in the opposite direction. 2. Addition of guinea-pig peritoneal eosinophils to the apical side of the tissues had no significant effect on the transmucosal flux of albumin in either the bronchial or tracheal mucosa. 3. When eosinophils were stimulated with the ionophore A23187 or by opsonic adherence to tissues treated with a guinea-pig anti-bovine airway epithelium antibody, the bronchial mucosal sheets that had been exposed showed a significant increase in the transmucosal flux of albumin. However, tissues from the tracheal mucosa were resistant to the effects of stimulated eosinophils. 4. Histologically, sheets of mucosa from bovine main bronchi that had been exposed to stimulated eosinophils were characterized by epithelial injury consisting of loss of columnar epithelium from the underlying basal cell layer and biomatrix. Much less evidence of cellular injury was observed in tracheal tissues. 5. Bacterial collagenases applied to the apical side of the sheets were shown to increase the permeability of the bronchial mucosa to albumin and to produce histological changes that had similarities with the pattern of damage produced by stimulated eosinophils. 6. These observations demonstrate that the ability of eosinophils to injure the bronchial mucosa is independent of the side of the tissue on which they are present. Furthermore, key aspects of the injury process may be reproduced, at least in part, by metalloproteinases.

Albumins↗
PubMed1993

Legume-associated residual cyst.

This report describes three unique cases of residual cyst (RC) which were characterized by large legume implants. To determine whether these represented a distinctive RC subset or if implanted materials have general importance in RC pathogenesis, a retrospective comparison of these cases and 37 further RCs with 40 control periapical cysts was performed. The frequency of foreign material implantation and the associated histopathologic features were assessed. No significant differences were noted suggesting that foreign implantations do not have an etiologically significant association with RCs and that the legume-associated RCs represent a unique subgroup. The relationship of the legume-associated RCs to the category of lesions variously termed giant cell hyaline angiopathy, oral pulse granuloma or hyaline ring granuloma is discussed.

Adult↗
PubMed1993

Distribution of fluoride in human dental calculus.

The distribution of fluoride in human dental calculus was investigated using a mechanical sampling technique and the fluoride electrode. The fluoride concentrations were highest at the outer surface of dental calculus and, then fell to a plateau for the interior of the calculus, rising again as the tooth surface was approached. The coefficient of variation of fluoride concentration was significantly greater in the sub- than in the supragingival calculus (p < 0.01). The supragingival calculus thus tended to show a smoother distribution profile for fluoride than the subgingival calculus. Total fluoride, average fluoride, and maximum fluoride concentrations were not significantly different in supra- and subgingival calculus. No significant different were observed between males and females.

Adult↗
PubMed1993

Blood transfusion does not have an adverse effect on survival after operation for colorectal cancer.

The effect of perioperative blood transfusion on cancer progression remains controversial because retrospective clinical studies have produced conflicting results. We have collected data prospectively on 379 patients undergoing curative surgery for colorectal adenocarcinoma and assessed the effect of variables, including blood transfusion, on survival. Univariate and multivariate survival analysis has been carried out. When the end-point for analysis used was death due to recurrent colorectal carcinoma and non-cancer deaths were censored, there was no difference in cancer-specific survival between transfused and non-transfused patients. Survival analysis was also carried out without censoring the non-cancer deaths and clearly demonstrated how the statistical analysis and data interpretation could be distorted by age-related non-cancer deaths. The incidence of recurrence of colorectal carcinoma was not greater in the transfused group than in the non-transfused group. We conclude that blood transfusion should not be withheld in colorectal surgery for fear of worsening the prognosis.

Adenocarcinoma↗
PubMed1992

Protein targeting across the three membranes of the Euglena chloroplast envelope.

A system has been developed for the import in vitro of precursor proteins into Euglena chloroplasts, which have three envelope membranes. Preparation of functional chloroplasts with intact envelope membranes has been optimized. Import of the precursor (50 kDa) for the tetrapyrrole biosynthesis enzyme porphobilinogen deaminase (PBGD), and processing to the mature size (40 kDa), occurred at 25 degrees C in the light and the presence of ATP, with an estimated efficiency of 62%. Pretreatment of the chloroplasts with proteases abolished this import, suggesting the involvement of specific protein receptors. The presequence of PBGD was found to be cleaved by Escherichia coli leader peptidase to an intermediate form (46 kDa). A construct in which the first 30 residues of the presequence (presumed to be the region removed by leader peptidase) had been deleted was no longer imported. Neither prePBGD nor the truncated precursor were imported into pea chloroplasts, although both bound to the pea chloroplast envelope. Conversely, a chimeric construct, in which the mature PBGD protein was fused downstream of the transit peptide for pea ferredoxin-NADP reductase, was efficiently imported into pea chloroplasts and processed to the mature size. However, this was not imported into Euglena chloroplasts, although again it bound to them. These results provide preliminary evidence for the possibility of two functional domains within the Euglena PBGD presequence. The implications of these findings with respect to the evolution of Euglena chloroplasts are discussed.

Amino Acid Sequence↗
PubMed1992

Carboxyl-terminal processing of the D1 protein and photoactivation of water-splitting in photosystem II. Partial purification and characterization of the processing enzyme from Scenedesmus obliquus and Pisum sativum.

The D1 polypeptide of photosystem II (PSII) is synthesized as a precursor that is processed by cleavage at the carboxyl terminus during assembly of the active PSII complex. A mutant of the green alga Scenedesmus obliquus, LF-1, inactive in water-splitting, lacks the D1 processing activity but assembles otherwise normal PSII complexes containing the precursor D1 molecule. We have isolated and partially purified a soluble protease from sonicated thylakoids of both wild-type S. obliquus and Pisum sativum which will process the precursor D1 molecule in PSII-enriched membranes from the LF-1 mutant to the mature size. After processing (but not before), photoactivation of these PSII membranes in the presence of manganese restores water-splitting to levels seen after photoactivation of PSII membranes from dark-grown, wild-type, cells. The protease is unable to process D1 in intact thylakoids from the LF-1 mutant but processes D1 if present during sonication of the thylakoids, indicating that processing of the carboxyl-terminal extension of D1 occurs in the lumen of the thylakoid. The processing protease from both S. obliquus and P. sativum is a single subunit enzyme of native molecular mass 33-35 kDa. Processing rate is optimal at pH 6.5. Processing in vitro is evident within 5 min and is markedly inhibited by millimolar concentrations of divalent cations (Cu, Zn greater than Mn greater than Ca, Mg) but not by any known inhibitors of the major classes of proteases. The protease is inactive against the precursors of other thylakoidal proteins and is thus distinct from the thylakoidal amino-terminal processing enzyme involved in the removal of transit peptides from cytoplasmically-synthesised proteins imported into the thylakoid lumen.

Algal Proteins↗
PubMed1992

Proton gradient-driven import of the 16 kDa oxygen-evolving complex protein as the full precursor protein by isolated thylakoids.

The biogenesis of the lumenal 16 kDa protein of the photosynthetic oxygen-evolving complex was analysed using an assay for the import of proteins by isolated thylakoids. The precursor protein is imported with high efficiency in the light in both the presence and absence of stromal extract. Import is almost completely blocked in the dark or if the uncoupler nigericin is present in the light. The data indicate that transport across the thylakoid membrane is driven by a proton motive force in which the proton gradient is the dominant component, and that the full precursor protein can be transported across the thylakoid membrane without prior cleavage by the stromal processing peptidase.

Biological Transport, Active↗
PubMed1992

Immunohistochemical investigation of epidermal growth factor receptor expression during periods of accelerated rat incisor eruption.

The effect of accelerated odontogenesis of the rat mandibular incisor on the expression of receptors for epidermal growth factor (EGF) was examined using specific monoclonal antibodies to the receptor molecule. Acceleration of odontogenesis was achieved by regular trimming of the tooth crown. At normal eruption rates the major area of cross-reactivity was over the secretory ameloblasts. Some labelling of the papilla and preameloblasts was evident. When proliferation was increased the major area of effect was at the preodontoblast/odontoblast boundary where there was a marked increase in labelling, initially at the proximal end of the cell adjacent to the basal lamina. The ameloblasts did not show such a dramatic increase in receptor numbers. Increase in labelling was also evident in the remainder of the papilla. The results suggest that an increase in proliferation with normal morphogenesis is associated with an overall increase in the numbers of EGF receptors, particularly in a population of cells immediately before and after elongation and differentiation of odontoblasts.

Ameloblasts↗
PubMed1992

The effect of periodontal disease on sulphated glycosylaminoglycan distribution in the sheep periodontium.

The glycosylaminoglycan (GAG) distribution in the soft periodontal tissues of the sheep was investigated topographically in healthy tissue and the changes associated with periodontal disease determined and correlated with increasing disease severity. Total sulphated GAG content was determined spectrophotometrically and the proportions of individual GAGS measured after separation by cellulose acetate electrophoresis. In healthy tissue, total sulphated GAG distribution was found to mirror that described previously for collagen, being highest in the gum-pad region and adjacent to alveolar bone. This changed markedly in relation to periodontal disease. Early disease-related changes in GAGs were first detected adjacent to alveolar bone. In severely diseases tissue, an overall increase in sulphated GAG, particularly in the gum-pad region, was present. Increasing disease severity was accompanied by a decrease in dermatan sulphate and a concomitant increase in the proportion of chondroitin-4-sulphate. These changes may be due to the combined effects of chronic inflammation and alterations to the mechanical loading of the tissue owing to loss of attachment.

Animals↗
PubMed1992

The thickness of the sound and periodontally diseased human cementum.

Cementum of teeth previously analysed for fluoride was re-examined in order to determine whether or not periodontal disease had affected the thickness of the tissue. In the periodontally diseased teeth the cementum was thinner than normal in the middle region of the root. The apical cementum, however, was significantly thicker in periodontally diseased than in the sound teeth of subjects over 60 yr old. This may account for the higher total fluoride levels previously reported in the apical cementum of these same teeth.

Adult↗