IL1RN genotype as a risk factor for joint pain in hereditary haemochromatosis?
Explore the source record for details and available documents.
Alleles↗
Biomedical subjects
E J Walker
Publications and source records attributed to E J Walker.
Cytokine-activated endothelium recruits osteoclast precursors.
Osteoclast precursors reach sites of osteoclast formation and remodelling via the vasculature and are therefore destined to encounter endothelium before migrating to the bone surface. Here we investigated the hypothesis that endothelium may be involved in the regulation of osteoclast precursor recruitment to sites of bone resorption. Osteoclast precursors in human peripheral blood were identified by their ability to form mature osteoclasts in 21-day cultures supplemented with RANKLigand, M-CSF, 1,25(OH)(2)-vitamin D(3), dexamethasone and prostaglandin E(2). Under control conditions few osteoclast precursors adhered to endothelial cells (the human bone marrow-derived endothelial cell line BMEC-1). However, BMEC-1 cells treated with the resorption stimulating cytokines IL-1beta and TNFalpha depleted the PBMC population of all osteoclast precursors. These results provide the first evidence that osteoclast precursors can adhere to endothelium and suggest that endothelium could play an important role in the recruitment of osteoclast precursors to sites of bone resorption.
Bone Marrow Cells↗
Sequence homology between encephalomyocarditis virus protein VPI and histidyl-tRNA synthetase supports a hypothesis of molecular mimicry in polymyositis.
The amino acid sequence of histidyl-tRNA synthetase, the Jo-I antigen of polymyositis, has been compared with that of the polyprotein of encephalomyocarditis virus (EMCV), an agent shown recently to produce polymyositis symptoms in mice. It is shown that there is significant sequence homology between a region of the synthetase formerly identified by us as a possible epitope and a region on the coat protein VPI of EMCV. The viral protein also shows significant sequence homology with several muscle proteins. Identification of the likely spatial location of the VPI sequence on the shell of the virus by comparison with two other picornaviruses whose three dimensional structures have been determined, reveals it to be homologous with known immunogenic sites on these viruses. Independent structural localisation of the possible epitope by comparison with two aminoacyl-tRNA synthetases, whose three dimensional structures are known, also reveals that the sequence in question is likely to be favourably placed on histidyl-tRNA synthetase to crossreact with appropriate antibodies. These findings provide more definitive evidence in support of our previous suggestion that molecular mimicry could explain the origin of serum antibodies to aminoacyl-tRNA synthetases in polymyositis and suggests a likely viral etiology for the disease.
Amino Acid Sequence↗
Sequence comparisons in the aminoacyl-tRNA synthetases with emphasis on regions of likely homology with sequences in the Rossmann fold in the methionyl and tyrosyl enzymes.
Amino acid sequences of aminoacyl-tRNA synthetases specific for 12 different amino acids have now been published. Differences in origin at the species and organelle level result in 20 distinct sequences being available for comparison. Some of these were compared in small groups as they were determined and, although some homologies were detected, it was generally concluded that there was surprisingly little sequence homology in this functionally related group of enzymes. We have made comparisons of all of the available sequences by using a combination of computer and manual alignment methods and knowledge of the sequences in the Rossmann fold region of methionyl-tRNA synthetase from E. coli and tyrosyl-tRNA synthetase from B. stearothermophilus, enzymes whose three-dimensional structures have been described. It emerges that all of the aminoacyl-tRNA synthetase sequences thus examined show considerable homology with each other over at least parts of this region, some over virtually all of it. We conclude that a great deal more similarity than had previously been suspected exists in these proteins. In particular, the alignments we have made strongly imply the existence of a mononucleotide binding site of the Rossmann fold configuration in all of the synthetases compared.
Amino Acid Sequence↗
Improved detection of anti-Jo-1 antibody, a marker for myositis, using purified histidyl-tRNA synthetase.
The increased detection of anti-Jo-1 antibody afforded by the use of the purified antigen, histidyl-tRNA synthetase, in counterimmunoelectrophoresis is demonstrated. Using purified antigen, anti-Jo-1 antibody was detected in the sera of 16/33 (48.5%) patients with confirmed myositis and in 20/45 (44.5%) patients with confirmed or possible myositis. This rate is approximately double that obtained with commercial thymus extracts both in this study and seven others reported in the literature. The presence of antibody shows marked correlation with the activity of myositis at the time of serum sampling and with the presence of interstitial lung disease. Detection rates are similar in patients with polymyositis and dermatomyositis both with and without additional connective tissue diseases.
Adult↗
Purification of bovine liver histidyl-tRNA synthetase, the Jo-1 antigen of polymyositis: size of the whole enzyme and its characteristic proteolytic fragments.
We have recently reported the marked increase in frequency which can be achieved in the detection of the anti-Jo-1 antibody of polymyositis in serum samples by replacing commercial mixtures of cytoplasmic and nuclear antigens with the purified antigen, histidyl-tRNA synthetase. The present paper describes a method for purifying this antigen and an investigation of its size. Molecular masses previously reported for the enzyme have varied from 85-154 kDa and subunit molecular masses varying from 40-77 kDa have been observed. Several of these fragments are of sizes similar to those of a number of other autoantigens commonly observed in connective tissue diseases. Since the clinical identification of these autoantigens often relies exclusively on size determination by Western blotting, we have characterized the commonly occurring fragments of histidyl-tRNA synthetase lest they confuse such identification. It is concluded that histidyl-tRNA synthetase, like many other aminoacyl-tRNA synthetases, is subject to severe proteolysis during extraction procedures. Several characteristic fragments (Mr = 80, 75, 61, 55, 50 and 45 kDa) result, a finding that provides a satisfactory explanation of the various values previously reported. The intact bovine enzyme is a dimer of molecular mass close to 160 kDa.
Amino Acyl-tRNA Synthetases↗
Reflections: what have we learned? The board perspective.
Explore the source record for details and available documents.
Governing Board↗
Polymyositis and molecular mimicry, a mechanism of autoimmunity.
The amino acid sequences of Escherichia coli histidyl-tRNA synthetase and alanyl-tRNA synthetase, two proteins recently identified as autoantigens in polymyositis, were compared by a computer alignment procedure with those of the 3600 proteins tabulated in the National Biomedical Research Foundation protein sequence database. Both proteins contain sequences long enough to function as epitopes that match sequences on viral and muscle proteins. The homology thus revealed not only lends strong support to mechanisms of autoimmunity that invoke the theory of molecular mimicry of viral proteins, but also suggests a rationale for the skeletal muscle target of polymyositis.
Alanine-tRNA Ligase↗
Characterization of digoxin binding and daunorubicin uptake by isolated mature rat cardiac myocytes.
Myocytes isolated from ventricular muscle of mature rat heart have been used for characterization of digoxin binding and to establish whether a relationship exists between digoxin binding and uptake of daunorubicin. High- and low-affinity digoxin binding sites have been identified; respectively, 0.9 +/- 0.1 X 10(7) sites/myocyte, Kd 70-77 nM and 7 +/- 2 X 10(7) sites/myocyte, Kd 1.4-1.7 microM. Myocytes accumulate daunorubicin to an intracellular concentration 30-40 times that in the medium. We find no evidence that saturation of digoxin binding sites alters daunorubicin uptake or that daunorubicin influences binding of digoxin. Alteration of sarcolemmal membrane properties is demonstrated by inhibition of amino acid transport reflected in protein synthesis rates. Calmodulin activation of phosphodiesterase appears insensitive to daunorubicin.
Amino Acids↗
Molecular weights of mitochondrial and cytoplasmic aminoacyl-tRNA synthetases of beef liver and their complexes.
In eukaryotes, multienzyme complexes containing five to nine aminoacyl-tRNA synthetase activities have frequently been reported. In this study, we report the existence, in bovine liver cytoplasm, of a multienzyme complex containing at least 16 activities which can be disrupted by homogenization to give rise to smaller complexes and noncomplexed synthetases. Determination of the size and component activity of these complexes and of the molecular weights of all 20 free synthetases suggests that the smaller complexes and free activities normally identified arise from the larger complex by well-defined stages during homogenization. We also show that similar, though not identical, complexes are found in bovine liver mitochondria and give the molecular weights of 16 mitochondrial synthetases.
Amino Acyl-tRNA Synthetases↗
Amino acid transport and protein synthesis in energetically-stable calcium-tolerant isolated cardiac myocytes.
Myocytes isolated by enzymic dispersion from adult rat ventricular tissue are shown to be energetically stable in the presence of 0.5 mM CaCl2. ATP and ADP content and rates of lactate production are comparable with those of intact myocardial tissue and consistent with these cells being tightly coupled. Addition of 2,4-dinitrophenol precipitates rapid changes in adenine nucleotide concentrations and a 10-fold increase in lactate production. Cardiac myocytes selectively transport neutral amino acids of the A and L classes. Transport of the amino acid analogue alpha-aminoisobutyric acid is an active, temperature-dependent and insulin-sensitive process. The apparent Km for alpha-aminoisobutyric acid transport is similar to that determined for embryonic cardiac cells. Mature myocytes incorporate labelled amino acids into cytoplasmic proteins with molecular weights ranging from 10 000 to 150 000. Newly synthesised protein is metabolically stable. The data establishes calcium-tolerant myocytes as an experimental system offering many advantages over whole hearts for short- and long-term studies of protein synthesis and catabolism.
Adenosine Diphosphate↗
Defaecation frequencies in Black, Indian, Coloured and White populations - what do they signify?
Using questionnaires covering a 7-day period, frequencies of defaecation were determined in a total of 2937 Black, Indian. Coloured and White subjects aged from 10 years upwards. It transpired that the overall frequency in rural Blacks was roughly twice that of Whites. Among rural Blacks defaecation frequencies of 5-7 per week were recorded in 16%, and from 1-3 per day in 80%. The corresponding figures among urban Blacks were 25% and 71%, among Indians 58% and 34%, among Coloureds 46% and 39%, and among Whites 59% and 29%. The wide differential in frequencies between Blacks and Whites is consistent with the wide differential prevailing in proneness to noninfective bowel diseases. On the other hand, Indians and Coloureds had defaecation frequencies little different on average from those of Whites, yet the former two populations are far less prone to bowel diseases. Hence caution must be exercised in correlating defaecation frequency with proneness to bowel diseases. Since bowel behaviour includes numerous aspects, defaecation frequency should not be regarded in isolation.
Adolescent↗
Location and properties of two isoenzymes of cardiac adenylate kinase.
Adenylate kinase catalyses the equilibrium 2ADP = ATP + AMP. There are two isoenzymes of adenylate kinase in bovine ventricular tissue, one cytoplasmic, the other mitochondrial. Mitochondrial subfractionation locates this isoenzyme between the mitochondrial membranes with fatty acid-CoA ligase. The cytoplasmic and mitochondrial isoenzymes are distributed in ratio 3:2, and both forms were purified to homogeneity. They differ principally by charge, Km values for ATP, ADP and AMP, pH-stability and -activity profiles, and susceptibility to the inhibitor adenosine pentaphosphoadenosine. The forward and reverse reactions show similar energies of activation for the cytoplasmic enzyme, but differ for the mitochondrial enzyme. The molecular weights are indistinguishable. An integrated mechanism is formulated whereby one isoenzyme suppresses the activation of fatty acid and the other enhances carbohydrate utilization in hypoxic myocytes.
Adenine Nucleotides↗
Field study of coccidial and rotaviral diarrhoea in unweaned piglets.
A study of diarrhoea in unweaned piglets was carried out in nine herds, with special reference to the enteropathogenic agents which could be demonstrated. Coccidial (Isospora suis) and rotaviral infections were both identified, either singly or in combination. More extensive studies of I suis infection were undertaken in two of the herds and it was found that diarrhoea occurred most commonly in five- to 14-day-old piglets. Piglets with I suis infection were not necessarily diarrhoeic but grew poorly compared to uninfected piglets. I suis infection in litters correlated with oocyst excretion in sows. In herds with I suis infection, amprolium and monensin were used in the sow ration to achieve control, and in one herd oral dosing of piglets with amprolium in the first three or four days of life was carried out.
Animals↗
Diarrhoea in unweaned piglets associated with rotavirus and coccidial infections.
Explore the source record for details and available documents.
Animals↗
The nature of the allosteric interactions of ribonuclease and its ligands.
The allosteric model for ribonuclease activity by Walker, Ralston & Darvey [(1975) Biochem.J. 147, 425--433; (1976) Biochem.J. 153, 329--337] involves the binding of a large number of molecules of substrate or substrate analogue to a series of allosteric sites on the enzyme. In the present paper, the nature of these allosteric interactions is investigated. The effects of ionic strength pH carbamoylation of lysine to homocitrulline and of deamidation of glutamine and asparagine on plots of velocity versus substrate concentration are examined and evidence is presented that the allosteric transition involves an electrostatic interaction between the negatively charged substrate molecules and the cationic groups on the enzyme.
Allosteric Site↗