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At least 73 records · Page 4Linked to original sources
PubMed1980

Impairment by covalent modification of the ability of Phaseolus vulgaris phytohemagglutinin to stimulate cultured human lymphocytes: a comparison of different forms of covalent modification.

Phytohemagglutinin (PHA) isolated from Phaseolus vulgaris has been modified by treatment with various chemical reagents and the modified proteins have been tested for their ability to stimulate peripheral lymphocytes from two healthy human donors, in vitro. Reaction of PHA with citraconic anhydride, S-methyl isothiourea, or 2-hydroxy-5-nitrobenzyl bromide produced derivatives which retained the ability to stimulate lymphocytes, at low concentrations. Acylation of the lectin with acetic anhydride or masking of the carboxyl side chains by reaction with glycinamide-carbodiimide impaired stimulation. When PHA was treated with N-bromosuccinimide or with tetranitromethane, the derivatives were ineffective as lymphocyte stimulants. Chemical modifications affected, in some cases, the quaternary structure of the lectin. Glycinamide-, homoarginine-, and nitro-PHA were tetramers whereas acetyl-, citraconyl-, and N-bromosuccinimide-treated lectin were dimers. Antinative lectin antiserum cross-reacted with all the modified proteins, except in the case of the N-bromosuccinimide derivative. The results show that, in the human lymphocyte transformation assay, the mitogenic property of PHA may depend on intact aspartic, glutamic, and tyrosine residues whereas lysine residues do not appear to be essential.

Acetylation↗
PubMed1976

Chemical modification of crude timothy grass pollen extract. I. Antigenicity and immunogenicity changes following amino group modification.

Glutaraldehyde modification was found to reduce the allergenic potency of crude timothy pollen extracts yet even highly substituted materials retained the capability of inducing the formation of allergen-specific antibody in animals. Experiments showed that these antibodies were capable of blocking skin test reactions to native timothy allergens in pollen-sensitive human volunteers. The value of glutaraldehyde-modified allergen extracts for use in desensitization vaccine therapy is discussed.

Aldehydes↗
PubMed1993

[Chemical modification of nucleic acids and the mutagenicity of modified bases, with special reference to permanganate- and bisulfite-mediated modifications].

Methods for modifying nucleic acids and their components with permanganate and with bisulfite are reviewed, with emphasis on work developed by the author's group of investigators. N(4)Aminocytidine, a nucleoside analog obtainable on bisulfite-hydrazine modification of cytidine, is a potent mutagen, and the mechanism of its action in the mutagenesis is discussed.

Manganese↗
PubMed1990

Towards an artificial cornea: surface modifications of optically clear, oxygen permeable soft contact lens materials by ammonia plasma modification technique for the enhanced attachment and growth of corneal epithelial cells.

The advent of high water content, oxygen permeable contact lens materials has made the intracorneal implants more feasible. A major obstacle encountered is the regrowth of a stable epithelium over the implant. Therefore, ammonia gaseous plasma modification technique was used to modify the surface chemical properties of soft contact lens material such as poly(2-hydroxyethyl methacrylate and methacrylic acid), PHEMA-MAA copolymer, in an attempt to enhance the cell attachment and growth of rabbit corneal epithelial cells.

Ammonia↗
PubMed1979

[Modelling modification of chemical mutagenesis in human cells. III. Linear index of protection as the standardized criterion of modification].

The effect of substances with radioprotective activity, APAETP 2,3 (aminopropylaminoethylthiophosphoric acid 2,3), APAETP 3,3 and cystaphos, on chromosome aberrations, induced by thioTEPA in the culture of human lymphocytes was investigated. It is shown that the obtained curves "concentration -- effect" for thioTEPA can be described by equations rho = 1 -- e-(KC + alpha)2 and X = E -(KC + alpha)2 --1 for aberrant cells and for chromosome breaks in the presence of the investigated substances. On the basis of comparison of angle coefficients of regression the unificated characteristic of the efficiency of chemical mutagenesis is proposed: the linear protection index (LPI), with generalizes the effect of modificators in chemical mutagenesis.

Cells, Cultured↗
PubMed1987

[Interaction of EcoRII restriction and modification enzymes with synthetic DNA fragments. IX. Cleavage of substrates with point modifications in the recognition site and flanking sequences].

Ability of the EcoRII restriction endonuclease to cleave 14-base-pair DNA duplexes with nucleotide substitutions in the recognition site CCA/TGG and in the adjacent base pair has been studied. Modifications leading to a local change in the substrate conformation (rU residue in and outside the recognition site, A.A- or A.C-pairs in the flanking sequence) reduce the rate of hydrolysis, the effect being maximal when the modified base pair is outside the recognition site. No digestion occurs when the internal dC-residue of the recognition site is 5-methylated in one or both strands. Replacement of dT residue in the EcoRII recognition site by dfl5U residue results in a dramatic inhibition of hydrolysis. Km and kcat for the cleavage of 14-base-pair DNA duplex have been determined. The cleavage rate of the dT-containing strand of the recognition site in 1.5 fold higher comparing with the dA-containing strand. The cleavage of both strands of the substrate by EcoRII endonuclease is confirmed to proceed in one enzyme-substrate complex.

Base Sequence↗
PubMedDate not supplied

[Role of changes in oxygen concentration during modification of cell reproductive death in vitro. 2. Modification of radiosensitivity during changes in the rate of oxygen consumption by cells].

A study was made of the role of changes in the concentration of oxygen occurring upon modification of radiosensitivity of cells in vitro using temperature (0-37 degrees C), incoupling agents and respiration inhibitors, and also upon stimulation of the oxygen consumption by microsomes. When cells were irradiated in suspension, monolayer, spheroid and roots of plants a change in the rate of the oxygen consumption by cells and a corresponding change in their oxygenation can contribute considerably to a radiomodifying effect.

2,4-Dinitrophenol↗
PubMed1996

A novel method for chemical modification of functional groups other than a carboxyl group in proteins by N-ethyl-5-phenylisooxazolium-3'-sulfonate (Woodward's reagent-K): inhibition of ADP-induced platelet responses involves covalent modification of aggregin, an ADP receptor.

The chemical reaction of N-ethyl-5-phenylisooxazolium-3'-sulfonate (Woodward's Reagent-K, WR-K) with a carboxyl group yields an enol ester that cannot be reduced by sodium borohydride in an aqueous solution, while other nucleophiles such as sulfhydryl, hydroxyl, amino, and imidazole groups, react with WR-K to yield unsaturated ketones that are capable of being reduced by sodium borohydride in an aqueous medium. Aggregin, a 100-kDa protein on the surface of human blood platelets has been identified as an ADP receptor. Autoradiography of the gels obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the samples of solubilized human blood platelets modified by WR-K and then reduced by tritiated sodium borohydride (NaB[3H]4) showed the presence of a prominent band corresponding to a 100-kDa radiolabeled protein. Labeling of platelets by WR-K and NaB[3H]4 was inhibited by ADP, ATP, and thiol group modifying reagents. WR-K blocked completely labeling of platelets by [beta-32P]-8-(4-bromo-2, 3-dioxo-butylthio)adenosine-5'-diphosphate, an ADP-affinity analog that selectively and covalently labels aggregin (Puri, R. N., Kumar, A., Chen, H., Colman, R. F., and Colman, R. W. (1995) J. Biol. Chem. 256, 24482-24488). WR-K also inhibited ADP-induced platelet shape change, aggregation, and mobilization of intracellular Ca2+ and blocked ADP-induced inhibition of stimulated adenylate cyclase activity. The results show conclusively that WR-K inhibited ADP-induced platelet responses by preventing binding of ADP to aggregin and suggest that ADP binding domain of aggregin contains an essential thiol group. The method of labeling proteins by WR-K and NaB[3H]4, hitherto not used to distinguish among functional groups modified by WR-K, offers a useful and convenient alternative to previously used ultraviolet spectral methods which cannot be used to investigate the modified proteins in intact cellular systems.

Adenosine Diphosphate↗
PubMed1985

Surface modification of proteins. Activation of monomethoxy-polyethylene glycols by phenylchloroformates and modification of ribonuclease and superoxide dismutase.

A single-step method of activation of monomethoxypolyethylene glycols suitable for its binding to polypeptides and proteins is proposed. Based on the reaction with 2,4,5-trichlorophenylchloroformate or p-nitrophenylchloroformate, it gives reactive PEG-phenylcarbonate derivatives. The PEG intermediate is stable on storage, the activating group is easily quantified,and the reaction with amino acid and proteins proceeds rapidly at pH near neutrality. The PEG derivatization of enzymes with this procedure is less inactivating than those previously reported. Ribonuclease and superoxide dismutase were modified and the effect of (a) bound polymer on clearance time in rats, (b) antibody recognition, and (c) on the enzymatic activity toward low and high molecular weight substrates were studied.

Amino Acids↗
PubMed1997

Modification of polystyrenic matrices for the purification of proteins. III. Effects of poly(vinyl alcohol) modification on the characteristics of protein adsorption on conventional and perfusion polystyrenic matrices.

Poly(styrene-divinylbenzene) (PS-DVB) chromatography matrices, CG1000sd 20-50 microns (TosoHaas), PLRP4000s 15-25 microns, PLRP4000s 50-70 microns (Polymer Laboratories) have been modified by the adsorption and crosslinking of poly(vinyl alcohol) (PVA) to create a matrix suitable for the attachment of dye ligands. The adsorption capacities of lysozyme and HSA on these Procion Yellow HE-3G dyed PVA modified PS-DVB matrices were measured at various flow-rates and the capacities were compared with a Procion Yellow HE-3G dyed OH-activated POROS 20, 20-micron matrix (PerSeptive Biosystems). The adsorption of small proteins was not hindered by the smaller pores of the CG1000sd beads, but as protein size increased, and at high flow-rates, a high mass transfer rate became more dependent on large pore size and small particle diameter.

Adsorption↗