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Biomedical subjects

D G Dearborn

Publications and source records attributed to D G Dearborn.

52 records · Page 3Linked to original sources
PubMed1982

Intramolecular interactions of amino groups in 13C reductively methylated hen egg-white lysozyme.

Reductive methylation of hen egg-white (HEW) lysozyme with [13C]formaldehyde and NaCNBH3 and subsequent 13C NMR spectroscopy reveal resonances for each of the mono- and dimethyl derivatives of the six lysyl epsilon-amino groups and the NH2 terminus. Each resonance has a unique chemical shift, pKa, and chemical shift change upon deprotonation. The assignment of the resonances arising from the N alpha,N-dimethyl and N alpha-monomethyl NH2 terminus has been made as have resonance assignments for the two lysyl residues which crystallographic studies indicate are involved in ion pair interactions (Imoto, T., Johnson, L. N., North, A. C. T., Phillips, D. C., and Rupley, J. A. (1972) in The Enzymes (Boyer, P. D., ed) 3rd Ed, Vol. 7, pp. 665-868, Academic Press, New York). One resonance, tentatively assigned to the lysine 1 (epsilon NH3+) which forms an ion pair with glutamic acid 7 (gamma COO-), has a highly perturbed chemical shift which shows a biphasic titration curve (N epsilon, N-dimethyl pKa values 10.0 and 2.6). A similar titration curve is observed for a N epsilon-monomethyl lysyl residue. The resonance for lysine 13 (epsilon NH3+), which forms an ion pair with the carboxyl terminus, leucine 129 (alpha COO-), has been assigned by removal of leucine 129 with carboxypeptidase whereupon only one pair of mono- and dimethyl lysyl resonances is greatly perturbed. The pKa of N epsilon,N-dimethyl lysine 13 is 9.3 in des-Arg-Leu-lysozyme in contrast to 9.8 for the intact enzyme. Thus, it appears that both of the intramolecular ion pairs predicted by x-ray crystallography exist in the solution structure of HEW lysozyme.

Amino Acids↗
PubMed1982

Characterization of a human cryoglobulin complex: a crystalline adduct of a monoclonal immunoglobulin G and albumin.

An unusual human cryoglobulin complex was characterized as a two-component system containing monoclonal immunoglobulin G (IgG) and serum albumin in a 1:2 mole ratio. This complex appeared to be an antibody-antigen complex, since the mole ratio was appropriate and the isolated Fab of the IgG associated with the albumin. The cryoglobulin apparently arose as a result of specific association and/or aggregation of the IgG albumin adduct, since the cryoglobulin complex formed a crystalline precipitate. The IgG and albumin were separated and characterized with respect to immunological cross-reactivities, sedimentation velocities, isoelectric properties, and amino acid composition. The extent of precipitation of the cryoglobulin complex was maximal at pH 7.8, was decreased by added ions including citrate, ethylenediaminetetraacetic acid, NaCl, and CaCl2, and was decreased by increasing temperature. Both the nature of the cold-precipitable complex and the solubility properties differed from those described for other cryoglobulins.

Antibodies, Monoclonal↗
PubMed1981

[13C]Methylated ribonuclease A. 13C NMR studies of the interaction of lysine 41 with active site ligands.

A unique resonance in the 13C NMR spectrum of [13C]methylated ribonuclease A has been assigned to a N epsilon, N-dimethylated active site residue, lysine 41. The chemical shift of this resonance was studied over the pH range 3 to 11, and the titration curve showed two inflection points, at pH 5.7 and 9.0. The higher pKa, designated pKa1, was assigned to the ionization of the lysyl residue itself while the pKa of 5.7, designated pKa2, was assigned on the basis of its pKa to the ionization of a histidyl residue which is somehow coupled to lysine 41. Both pKa values are measurably perturbed by the binding of active site ligands including nucleotides, nucleosides, phosphate, and sulfate. In most cases, the alterations in pKa values induced by the ligands were larger for pKa2. The ligand-induced perturbations in pKa2 generally paralleled those reported for histidine 12, another active site residue (Griffin, J. H., Schechter, A. N., and Cohen, J. S. (1973) Ann. N. Y. Acad. Sci. 222, 693-708). The sensitivity of the N epsilon, N-dimethylated lysine 41 resonance to the histidyl ionization may result from a conformational change in the active site region of ribonuclease which is coupled to the histidyl ionization. This coupling between lysine 41 and another ribonuclease residue, which has not been documented previously, offers new insight into the interrelationship between residues in the active site of this well characterized enzyme.

Animals↗
PubMed1980

Ultrastructure and function of alveolar macrophages from cystic fibrosis patients.

Alveolar macrophages were isolated from three cystic fibrosis patients, and the structure and function of these cells were compared to that of normal alveolar macrophages. The cystic fibrosis (CF) and normal alveolar macrophages were able to phagocytize Pseudomonas in the presence of normal serum, but cells from both sources had decreased phagocytosis of Pseudomonas in the presence of CF serum. Phagocytosis of Staphylococcus was not inhibited. Ultrastructural studies showed CF macrophages to be morphologically normal, however, in contrast to CF polymorphonuclear cells, they had not been heavily engaged in phagocytosis. The similarities between CF and normal macrophages suggest that the chronic pulmonary infection of CF may be due to an extrinsic factor in an altered lung environment rather than to any intrinsic cellular defect of the alveolar macrophage.

Adolescent↗
PubMed1980

Saliva from patients with cystic fibrosis inhibits amiloride-sensitive sodium transport.

A factor is present in the saliva and sweat from patients with cystic fibrosis (CF) which inhibits the reabsorption of sodium in the ducts of the salivary and sweat glands. Inasmuch as the physiology of sodium absorption is similar in salivary ducts and the distal colon, we have examined the sensitivity of the sodium absorption in the rat colon to saliva from CF patients. Sodium absorption by the rat colon, estimated as the shortcircuit current, was inhibited by saliva from both patients with CF and normal volunteers. However, only with CF saliva was the inhibition consistently proportional to the saliva concentration. Furthermore, the inhibitory activity of CF saliva was greater than the inhibition observed with saliva from age- and sex-matched controls (percentage of inhibition: CF = 20.1 +/- 2.2, and controls = 14.9 +/- 2.1; P < 0.02), and the inhibition of the colonic shortcircuit current was proportional to the activity measured by the ductal retrograde perfusion assay with the rat parotid gland (linear correlation coefficient = 0.634; P < 0.005). This latter assay is an accepted assay for CF factor activity. We conclude that the CF factor present in saliva probably interacts in a reversible manner with the amiloride-sensitive sodium transport system which is present in all sodium scavenging epithelia. The rat colon is a promising assay system for CF factor activity because the electrical measurements permit a rapid quantitative estimate of activity and a single piece of tissue can be used to measure the activity of several saliva samples.

Amiloride↗
PubMed1979

Inhibitory effect of cystic fibrosis serum on pseudomonas phagocytosis by rabbit and human alveolar macrophages.

This report presents experimental observations indicating the presence of an inhibitory activity in cystic fibrosis (CF) serum which impairs phagocytosis of Pseudomonas aeruginosa by rabbit as well as human alveolar macrophages. Of the 49 patient serum samples studied, 40 consistently showed greater than or equal to 60% inhibition, 3 showed no inhibition and 6 were in the range of 20-60% inhibition of Pseudomonas phagocytosis. In parallel studies, the phagocytosis of S. aureus and S. marcescens was found not to be inhibited by CF serum. Mixing of CF serum with normal serum could not overcome the inhibitory effect, indicating the presence of an inhibitory factor rather than the lack of a necessary component. The inhibitory activity is not lost upon exposure of serum to glass, upon freezing the serum once, or upon heating at 56 degrees C for 30 minutes.

Adolescent↗
PubMed1976

Lipophosphonoglycan of the plasma membrane of A canthamoeba castellanii. Inositol and phytosphingosine content and general structural features.

Lipophosphonoglycan, a major component of the plasma membrane of Acanthamoeba castellanii, has now been shown to contain 8% inositol and 13% C25- and C24-phytosphingosines in addition to the previously identified content of neutral sugars (26%), amino sugars (3%), aminophosphonates (10%), acidhydrolyzable phosphate (3%), and long chain fatty acids (14%). The fatty acids and phytosphingosines are in ceramide groups. Lipophosphonoglycan can be separated by dodecyl sulfate-polyacrylamide electrophoresis into two major components that are similar in composition except for different oligosaccharide groups. A tentative structural model incorporating these features is proposed in which each of the two components of lipophosphonoglycan is conceived as an oligomeric inositol-containing glycosphingolipid.

Amoeba↗
PubMed1969

Reversible thermal conformation changes in human serum low-density lipoprotein.

Human serum beta(1) (LDL(2)) lipoprotein was preparatively divided into three subfractions on the basis of density, and the protein conformation was investigated by optical rotatory dispersion and circular dichroism. The protein conformation was found to vary substantially as a function of lipid composition and temperature in a gradual and reversible manner. Surprisingly, the reversible temperature range includes physiological temperature. From the character of the spectra, it appears that alpha-helix, disordered, and beta conformations can be present in the protein moiety. The presence of these conformations and their distribution appears to depend upon both lipid content and temperature. The importance of this conformational flexibility in its relation to the role of the lipoprotein in lipid transport is discussed.

Chemical Phenomena↗
PubMedDate not supplied

Suppression of lymphocyte proliferation by Pseudomonas aeruginosa phenazine pigments.

Pseudomonas aeruginosa culture supernatants have been shown to inhibit lymphocytes proliferation as measured by [3H]TdR uptake. The phenazine pigment pyocyanine has been identified as one of the inhibitors present in those supernatants. To determine the mechanism of the inhibitory action of P. aeruginosa supernatants and pyocyanine, we studied their effect on the early stages of T-cell activation. Both P. aeruginosa supernatant and pyocyanine inhibited lymphocyte stimulation induced by the lectin concanavalin A. Analysis of Interleukin-2 receptor expression on the T-cell membrane showed that it was inhibited by both. This inhibition is dose dependent and not due to cellular toxicity. There was a parallel inhibition of growth in cell volume as well as [3H]TdR uptake. The results reported here suggest that P. aeruginosa culture supernatant and purified pyocyanine may interfere with cellular immune responses that may be necessary for eradication of chronic infection with P. aeruginosa in patients with cystic fibrosis.

Antibodies, Monoclonal↗