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Biomedical subjects

R C Williams

Publications and source records attributed to R C Williams.

At least 235 records · Page 13Linked to original sources
PubMed1986

The effects of elevated pH and high salt concentrations on tubulin.

The effects of incubating phosphocellulose-purified bovine tubulin at 4 degrees C in nucleotide-free buffers at alkaline pH or at high concentrations of NaCl, KCl, (NH4)2SO4, or NH4Cl have been studied. At pH greater than or equal to 7.5 or at NaCl concentrations greater than or equal to 0.7 M, tubulin releases bound nucleotides irreversibly and loses, with apparent first-order kinetics, the ability to assemble into microtubules. In 0.1 M 1,4-piperazinediethanesulfonic acid buffer, pH 6.9, in the presence of 1.3 M NH4Cl, tubulin undergoes more rapid loss of capacity to assemble than it does in NaCl and KCl, but 1.3 M (NH4)2SO4 causes no detectable change in tubulin after 1-h incubation. Incubation at high pH or at high neutral salt concentrations also causes an apparently irreversible change in the ultraviolet difference spectrum and in the sedimentation velocity profile of tubulin. At elevated salt concentrations a decrease of approximately 10% in the molar ellipticity within the wavelength range 220-260 nm is observed. The changes that occur during 1-h exposure to pH 8.0 can be completely prevented by including 1 mM guanosine 5'-triphosphate (GTP) or 4 M glycerol in the buffer, but those which occur at pH 9.0 cannot be prevented by these additions. In 1 M NaCl when the ratio of bound guanine nucleotide to tubulin reaches approximately 1.0, tubulin loses the abilities to assemble into microtubules and to bind colchicine. The rate of loss of nucleotide in 2 M NaCl is decreased in the presence of 1 mM GTP, and tubulin is protected almost completely from 1 M NaCl-induced loss of GTP (and retains the ability to exchange [3H]GTP as well) in the presence of bound colchicine. Investigators who anticipate exposing tubulin to buffers of elevated pH or high concentrations of chaotropic salts should be extremely cautious in interpreting the resulting data unless they can demonstrate that irreversible alteration of the protein has not occurred.

Colchicine↗
PubMed1986

Changes in anti-lymphocyte and anti-Ia antibodies during pregnancy in systemic lupus erythematosus.

Anti-lymphocyte antibodies reactive with monocyte-depleted lymphocytes, T cells, or B cells were studied in 43 nonpregnant and 23 pregnant systemic lupus erythematosus (SLE) patients. Anti-Ia specificity was assayed in an enzyme-linked immunosorbent assay system. No difference in mean lymphocytotoxicity was noted between pregnant and nonpregnant SLE patients; however, anti-Ia lymphocyte antibody associated with disease activity was lower (P less than 0.01) in pregnant than in nonpregnant SLE patients. Lymphocytotoxic or anti-Ia antibody activity did not reliably predict the outcome of individual pregnancies.

Antilymphocyte Serum↗
PubMed1986

Defective T-lymphocyte chemotactic factor production in patients with established malignancy.

Lymphocytes from 22 patients with established malignancy were stimulated with concanavalin A (Con A), and supernatants were tested for T-lymphocyte chemotactic factor (LCF). LCF activity was measured using a leading front chemotaxis assay with normal human T cells as responders. Fifteen of the 22 patients tested produced LCF at a level of less than 2 standard deviation below the mean of control cells. In 10 patients where mononuclear cells were stimulated with Con A for 24, 48, and 72 hr, LCF activity was significantly reduced at all three time points averaging 38, 14, and 43% of control levels, respectively. In 13 of the 31 patients, patient T-cell migration in response to casein was measured and compared to the production of LCF by mononuclear cells from these same patients. A significant correlation was observed indicating that both the response of T cells to a migration stimulus, and the production of T-cell-derived LCF was comparably suppressed. The reduction in LCF production by mononuclear cells from patients with established malignancy was not reversed by the addition of indomethacin to the culture system during Con A stimulation indicating that inhibition was not mediated by excessive prostaglandin production. The addition of patient mononuclear cells or T cells to normal mononuclear cells resulted in the inhibition of normal cell LCF by patient mononuclear cells or T cells. This could not be attributed to the production of a lymphocyte chemotactic inhibitor by patient cells, but appeared instead to be due to the direct inhibition of normal cell LCF synthesis or release by patient mononuclear cells or T cells. Separation of patient T cells into Leu 2 suppressor/cytotoxic or Leu 3 helper/inducer T cells showed that the inhibitory activity was associated with the Leu-2 T-cell subset. Heterologous normal Leu 2 T cells did not suppress normal mononuclear cell LCF production suggesting that patient Leu 2 T cells were functionally activated as compared to normal Leu 2 cells. The decreased production of LCF coupled with a depressed T-cell migratory activity in patients with established malignancy may in part be responsible for suppressed cellular immune reactions in these patients and possibly the impairment of tumor rejection.

Adolescent↗
PubMed1986

Absence of interferons-alpha and -gamma in renal lesions of systemic lupus erythematosus and membranous glomerulonephritis.

Frozen kidney biopsy sections from nine patients with systemic lupus erythematosus (SLE) as well as many other renal diseases, including IgA nephropathy, membranous nephritis, and minimal change nephrotic syndrome, were negative for interferons -alpha and -gamma by immunofluorescence. Lupus patients studied included several subjects with marked serum elevations of interferon activity as well as others with low or negative serum interferon levels. Isolated glomerular eluates prepared from normal and SLE kidneys showed no functional interferon activity by virus plaque inhibition assay. Components of normal as well as SLE serum showed no direct binding to interferon -alpha or -gamma by ELISA assays.

Arthritis, Rheumatoid↗
PubMed1986

Human anti-F(ab')2 antibodies and pepsin agglutinators react with Fv determinants.

Affinity-purified human IgG anti-tetanus antibody was subjected to papain and then pepsin digestion, and residual fragments retaining antibody activity were re-isolated by adsorption and elution from Sepharose-tetanus toxoid columns. Both Fab' and Fv fragments isolated by gel filtration showed strong reactivity with anti-F(ab')2 antibodies. Failure of tetanus toxoid to completely block reactivity of anti-F(ab')2 antibody with anti-tetanus Fv fragments indicates that these antibodies react with framework antigens within variable antibody regions.

Antibodies, Anti-Idiotypic↗
PubMed1986

Gm 3;5,13,14 and stated-admixture: independent estimates of admixture in American Indians.

Bernstein's formula for the estimation of the amount of admixture (m) in a hybrid population has been used frequently since its publication in 1931. While mathematically correct, it has not been shown to be correct in practice, because an independent estimate from a large sample has not been available. We have compared the estimate of m for Caucasian admixture derived by using Bernstein's formula with that estimated from stated-admixture (Sa) within a sample of 5,759 Native Americans. There was a linear relationship between the two variables (m = -.000275 + .714Sa; r = .976 for the grouped data, P = .0001).

Gene Frequency↗
PubMed1985

Mechanism of microtubule assembly. Changes in polymer structure and organization during assembly of sea urchin egg tubulin.

Assembly of tubulin, purified from eggs of the sea urchin Stronglyocentrotus purpuratus, was examined at physiological (18 degrees C) and nonphysiological (37 degrees C) temperatures. Critical concentrations for assembly were 0.71 mg/ml at 18 degrees C and 0.21 mg/ml at 37 degrees C. At tubulin concentrations above 1.2 mg/ml at 18 degrees C and 0.5 mg/ml at 37 degrees C, a concentration-dependent "overshoot" in turbidity and in small-angle light scattering was observed; turbidity and scattering increased rapidly to a peak, then decreased asymptotically toward a steady-state value. Quantitative sedimentation analysis revealed that the mass of assembled polymer reached and maintained a constant level during overshoot of turbidity. Changes in the wavelength dependence of turbidity were consistent with the initial formation of sheets of tubulin, followed by conversion of the sheets to microtubules, both at 18 and 37 degrees C. Examination by negative-stain electron microscopy showed that sheetlike structures predominated during the early stages of overshoot assembly, while complete microtubules were present at steady state. Furthermore, measurements of average polymer length revealed that the overshoots in turbidity and in light scattering are unlikely to be caused by polymer length redistribution. Qualitative observations of solution birefringence suggested that the polymer became progressively more aligned during assembly. These results suggest that the turbidity/light-scattering overshoots reflect changes in the form or in the organization of the assembling polymer, or both.

Animals↗
PubMed1985

Formation of microtubules at low temperature by tubulin from antarctic fish.

Tubulin was isolated from two species of antarctic fish, Pagothenia borchgrevinki and Dissostichus mawsoni, by cycles of temperature-dependent assembly, centrifugation, disassembly, and centrifugation. The preparations were found to consist almost entirely of tubulin and to contain negligibly small amounts of microtubule-associated proteins. This tubulin polymerized to make microtubules of ordinary dimensions. The formed microtubules appear to be in labile equilibrium with free tubulin dimer at all temperatures observed. In a buffer consisting of 0.1 M 1,4-piperazinediethanesulfonic acid, 2 mM dithioerythritol, 1 mM MgSO4, 2 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and 1 mM guanosine 5'-triphosphate, pH 6.9, the tubulin of P. borchgrevinki has a critical concentration for assembly of 0.046 (+/- 0.008) mg/mL at 35 degrees C and 0.74 (+/- 0.15) mg/mL at the habitat temperature of the fish, -1.8 degrees C. The critical concentration measured at the lower temperature is quite small relative to the critical concentration for formation of mammalian microtubules from pure tubulin at the same temperature, which must be at least 2 orders of magnitude larger. The antarctic fish microtubules may thus be called "cold stable" by comparison with mammalian microtubules. They do not fully dissociate at temperatures near 0 degree C because they are composed of tubulin that assembles more readily at these temperatures than does mammalian tubulin. There is no evidence for the presence of a cold-stabilizing factor in association with the tubulin. These findings suggest that alteration of tubulin may be a means by which some poikilotherms can adapt to a cold environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Characterization of oligomers of tubulin by two-dimensional native electrophoresis.

We and others [Lee et al. (1973) J. Biol. Chem. 248, 7253-7262; Kravit et al. (1982) J. Cell Biol. 95, 344a; Kravit et al. (1984) J. Cell Biol. 99, 188-198] have observed oligomers of tubulin by native polyacrylamide gel electrophoresis (PAGE), even when they were not evident in sedimentation velocity or gel-exclusion chromatography experiments under comparable conditions. Aggregates of tubulin are also seen on native starch gels. Tubulins purified from calf brain, sea urchin egg (Strongylocentrotus purpuratus), and antarctic fish brain (Pagothenia borchgrevinki) give rise to similar distributions of aggregates. Unlike microtubules, these oligomers are relatively insensitive to temperature (5-25 degrees C), pH (6.1-8.8), the absence of excess GTP and/or Mg+2, stoichiometric concentrations of colchicine, and a variety of electrophoresis buffers. These aggregates, once formed during electrophoresis, associate and dissociate slowly. Depending upon the incubation conditions, they give rise to kinetically controlled distributions that appear in two-dimensional native PAGE as a square array of discrete polymeric species. The fastest migrating species (monomers) are often observed to reequilibrate preferentially into the second band. The second band reequilibrates into the fourth, the third band into the sixth, the fourth into the eighth, etc. (The assignment of molecular weights to these species by Ferguson analysis is tentative due to their slow reequilibration.) Thus, a feature of the reequilibration is that association occurs more rapidly than dissociation and each species is occasionally observed to "dimerize." This behavior is suggestive of irreversible aggregation (possibly crosslinking) or of the formation of slowly dissociating aggregates. Although they may be related to the protofilaments of microtubules, these oligomers appear to be another example of nonmicrotubular, polymorphic aggregates of tubulin.

Animals↗
PubMed1985

Flurbiprofen: a potent inhibitor of alveolar bone resorption in beagles.

The nonsteroidal anti-inflammatory drug, flurbiprofen, a potent cyclooxygenase inhibitor, significantly decreases the resorption of alveolar bone in naturally occurring chronic destructive periodontal disease in beagles. This observation indicates that arachidonic acid metabolites are important in the alveolar bone loss of periodontitis and suggests a use for flurbiprofen in the management of bone resorption disease.

Alveolar Process↗