Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induced by phorbol myristate acetate (PMA) to a greater extent than they inhibit mitogenesis induced by concanavalin A or phytohemagglutinin. These agents include dimethyl sulfoxide, benzoate, thiourea, dimethylurea, tetramethylurea, L-tryptophan, mannitol, and several other alcohols. Their inhibitory effect is not associated with cytotoxicity. The hydroxyl radical scavengers do not inhibit PMA-dependent amino acid transport in T cells or PMA-induced superoxide production by monocytes. Thus, they do not inhibit the primary interaction of PMA with responding cells. Treatment of peripheral blood mononuclear cells with PMA increased cellular guanylate cyclase in most experiments, and dimethyl sulfoxide tended to inhibit this increase. In addition to inhibition of PMA-induced mitogenesis, hydroxyl radical scavengers markedly inhibited the activity of lymphocyte activating factor (interleukin 1). The differential inhibition of lymphocyte mitogenesis induced by different mitogens appears to be related to the differential macrophage requirements of the mitogens. The data suggest that hydroxyl radicals may be involved in mediating the triggering signal for lymphocyte activation. Some of the hydroxyl radical scavengers are inducers of cellular differentiation,. nd it is possible that their differentiating activity is related to their ability to scavenge free radicals. (+info)
Hydrophobic interactions and the adherence of Streptococcus sanguis to hydroxylapatite.
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Streptococcus sanguis demonstrated a high affinity for hydrocarbon solvents. When aqueous suspensions of the organism were mixed with either hexadecane or toluene, the cells tended to bind to the nonaqueous solvent. Increases in temperature resulted in a greater affinity of cells for hexadecane. Interaction between the cells and hexadecane was also enhanced by dilute aqueous sodium chloride and by low pH (pH less than 5). The results suggest that the cell surface of S. sanguis has hydrophobic properties. Isolated cell walls also tended to partition into the nonaqueous solvent. Amino acid analyses of the walls revealed the presence of several amino acids which possess hydrophobic side chains. It is likely that the hydrophobic amino acids associated with the cell wall contribute to the hydrophobicity of intact S. sanguis. When the adherence of S. sanguis to saliva-coated hydroxylapatite was measured, it was found that hydrophobic bond-disrupting agents, such as the Li+ cation, the SCN- anion, and sodium dodecyl sulfate, were capable of inhibiting the cell-hydroxylapatite union. In addition, it was observed that both urea and tetramethylurea were inhibitors of the adherence, although the latter reagent was the superior inhibitor. The results suggest that the adherence of S. sanguis to saliva-coated smooth surfaces is at least partially dependent on the formation of hydrophobic bonds between the cell and adsorbed salivary proteins. Hydrophobic bonding may contribute to cooperative interactions involving S. sanguis and saliva-coated hydroxylapatite (Nesbitt et al., Infect. Immun. 35:157-165, 1982). (+info)
Hydroxyl radical scavengers produce similar decreases in the chemiluminescence responses and bactericidal activities of neutrophils.
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The addition of hydroxyl radical (.OH) scavengers caused similar decreases in the chemiluminescence responses and killing of Staphylococcus aureus 502A by human neutrophils in vitro. (+info)
Involvement of lysine residues in the binding of ovine chorionic somatomammotropin to lactogenic and somatotropic receptors.
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The biological activities of several ovine chorionic somatomammotropin (oCS) derivatives obtained by chemical modification of the lysine residues were studied by radioreceptor assays using rabbit mammary homogenates (lactogenic activity, L.A.) and liver homogenates (somatotropic activity, S.A.). Even if the control treatment with BH-4 markedly decreased the L.A., it was clear that methylation mainly affected the S.A. and that ethylation reduced both activities. Guanidination inactivated almost completely both activities and acetimidination at a very low degree (3 of 14 lysines) led to less than 50% of both activities. These results show the involvement of lysine residues in the interaction of oCS with lactogenic and somatotropic receptors. (+info)
Inhibition of phorbol ester-mediated interleukin-2 production by cellular differentiating agents.
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Lymphocyte proliferation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is inhibited by agents known to induce differentiation in murine erythroleukemia cells and other cell lines. In the present study, we determined the cellular targets for the action of TPA among murine thymocyte subpopulations, the phase of blastogenesis that is activated by the tumor promoter, and the phase that is inhibited by the differentiating agents. Mouse thymocytes were fractionated into populations bearing receptors for peanut agglutinin (PNA; PNA-positive cells) and populations lacking such receptors (PNA-negative cells). TPA is comitogenic for lectin-treated, unfractionated thymocytes and PNA-negative thymocytes but not for PNA-positive thymocytes. PNA-negative cells, a minor population in unfractionated thymocytes, are therefore the cellular targets for the comitogenic activity of TPA. TPA induces the production of interleukin-2 (IL-2) in lectin-treated PNA-negative populations but not in PNA-positive cells. The differentiating agents inhibit TPA-mediated proliferation of unfractionated and PNA-negative, lectin-treated thymocytes. In contrast, IL-2-mediated proliferation of lectin-treated thymocyte subpopulations is resistant to inhibition by these agents. Inhibition appears to be related to decreased production of IL-2, since the differentiating agents inhibit IL-2 production by both PNA-negative thymocytes and by a human leukemic cell line. (+info)
The measurement of apolipoprotein A-I in human plasma by electroimmunoassay.
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A variable proportion of the total apolipoprotein A-I (apo A-I) present in plasma or high density lipoproteins (HDL) is normally detectable by immunochemical methods. This has been attributed to masking of some of the immunoreactive sites of apo A-I by lipid in the intact HDL particle. This difficulty has been circumvented by heating or delipidation. We find that exposure of plasma to concentrations of urea greater than about 7.0 M in the barbital buffer used to dilute plasma samples for estimation by electroimmunoassay enables the complete detection of Apo A-I, as judged by comparison with samples delipidated with tetramethylurea. The need for time-consuming heating or delipidation is avoided. (+info)
1,1,3,3-Tetramethylurea and triethanolamine as a new useful matrix for fast atom bombardment mass spectrometry of gangliosides and neutral glycosphingolipids.
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Analysis of gangliosides from bovine brain was successfully performed by a newly developed method of fast atom bombardment mass spectrometry (FAB-MS). The use of triethanolamine with a few drops of 1,1,3,3-tetramethylurea as the matrix solution gave intense molecular ions of intact gangliosides tested, namely, GM1 and GD1a, corresponding to (M + Na)+ and (M + 2Na-H)+. Glycerol, that is usually used as a matrix solution for FAB-mass spectrometry, was not suitable for the analysis of gangliosides. Along with the molecular ion species, the ions pertaining to the carbohydrate sequence also appeared on the spectrum. The method was found to be useful for structural analysis using intact molecules of gangliosides and neutral glycosphingolipids. (+info)
The selectivity of amino acid and peptide amidination with O-methylisourea.
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Selectivity of amidination using ornithine as model amino acid was investigated in detail. The results obtained were taken advantage of for studying the reactions with other polyfunctional amino acids: beta-tyrosine, isoserine, 2,3-diaminopropionic acid, 2,6-diamino-7-hydroxyazelaic acid and with the pentapeptide amide, edeine A. It was found that, if the appropriate conditions are maintained, selective amidination of more basic amino groups of polyamino compounds is possible when these groups are bound to the primary alkyl. (+info)