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Biomedical subjects

M Wilchek

Publications and source records attributed to M Wilchek.

At least 163 records · Page 9Linked to original sources
PubMed1979

Involvement of gangliosides in lymphocyte stimulation.

N4-Dinitrophenyl-L-2,4-diaminobutyric acid hydrazide was attached covalently to the aldehyde groups produced by periodate oxidate of bovine brain gangliosides and it was incorporated into mature thymocytes. High concentrations of antibodies to dinitrophenyl (DNP) or lower concentrations followed by protein A agglutinated the cells and stimulated DNA synthesis. Incubation of the thymocytes containing DNP-modified ganglioside with rabbit anti-DNP and fluorescein-labeled anti-rabbit IgG resulted in the formation of uniform rings on the cell surface, which subsequently developed into patches and caps. These results indicate that gangliosides may play a primary role in the lymphocyte activation process.

Agglutination↗
PubMed1978

Modulation of the catalytic properties of alpha-chymotrypsin by chemical modification at Tyr 146.

alpha--Chymotrypsin was modified with three different diazonium salts derived from D--phenylalanine. All three reagents react selectively with tyrosine 146 on the surface of the enzyme. The spectral and enzymatic properties of the azochymotrypsins are characteristic for each of the proteins. Dependent on the structure of the reagent employed for modification, the activity towards rho-nitroanilide substrate can be higher or about the same as that of the native enzyme.

Amino Acid Sequence↗
PubMed1978

Specific localization and quantification of biotin transport components in yeast by use of a biotin-conjugated, impermeant, electron-dense label.

Two approaches are described for the localization and quantification of biotin transport components in yeast cells. One approach is based on tracing the fate of a radioactive affinity label for the biotin transport system, [14C]biotinyl-p-nitrophenyl ester (pBNP), through various stages of subcellular fractionations. A complementary method involves the use of a biotin-derivatized, impermeant, electron-dense, affinity-cytochemical label (ferritin-biotin conjugates) for subsequent visualization by electron microscopy. Values of approximately 8,000 and 4,000 sites/cell, respectively, were achieved by the two methods. Complicating factors, future perspectives and the relevance of the two methods to the isolation of transport components are discussed.

Affinity Labels↗
PubMed1978

Modification of a specific tyrosine residue of ribonuclease A with a diazonium inhibitor analog.

The diazonium salt of 5'-(4-aminophenyl phosphoryl)-uridine 2'(3')-phosphate reacts stoichiometrically with pancreatic ribonuclease and modifies only one tyrosyl residue, which was identified as Tyr 73 in the amino acid sequence. The modification does not inhibit the biological activity of RNAase on ribonucleic acid, although a large change in the binding constant towards cytidine cyclic phosphate was observed. The modification can be inhibited by addition of the competitive inhibitor cytidine 2'(3')5'-diphosphate and may indicate that Tyr 73 is the most exposed residue or has a unique reactivity towards this reactive substrate analog.

Amino Acids↗
PubMed1978

Grafting of triggering sites onto lymphocytes: requirement of multivalency in the stimulation of dinitrophenyl-modified thymocytes by anti-dinitrophenyl antibody.

N4-Dinitrophenyl-L-2,4,-diaminobutyric acid hydrazide was coupled to aldehyde groups generated by periodate oxidation of sialyl residues on thymocytes. Anti-2,4-dinitrophenyl(Dnp)antibody was found to stimulate mature, hydrocortisone-resistant thymocytes, while it had no mitogenic effect on the immature thymocytes. In order to study the involvement of different regions of the antibody molecule in the triggering process of stimulation, the mitogenicity of various antibody fragments was also assessed. The divalent F(ab')2 was found to be a superior mitogen compared to the intact antibody when added to Dnp-conjugated thymocytes. The monovalent Fab' and Fab fragments have no mitogenic activity indicating that cross-linkage may be a prerequisite for stimulation.

Animals↗
PubMed1978

Analysis of hog thyroglobulin. Identification of galactosamine and absence of lysinoalanine, a potential product of tyrosine coupling.

A small peak in the amino acid analysis of hog thyroglobulin was observed in the region reported for lysinoalanine and galactosamine. Since galactosamine had been previously reported absent in hog thyroglobulin, the possibility that this peak was lysinoalanine, a potential product of the coupling of two iodotyrosines, was investigated. Tests, however, showed that the material was galactosamine and that hog thyroglobulin contains no significant amount of lysinoalanine. Approximately 5 moles of galactosamine were found per mole of thyroglobulin.

Animals↗
PubMed1978

Higher antitumor efficacy of daunomycin when linked to dextran: in vivo and in vitro studies.

Daunomycin was coupled to dextrans of various molecular sizes. The binding to the dextran carriers augmented the therapeutic efficacy of the antitumor agent in a murine lymphoma line (YAC). When the treatment with the drug or its conjugates was given concomitantly with the tumor cells at separate sites, the unbound drug was able, at its optimally effective doses, to prevent tumors in 40% of the mice, whereas the drug-dextran was efficient in 80% of the mice. The advantage of the drug-dextran over the free drug was also manifested when the treatment was given 6 days after tumor transplantation. However, a further delay of the treatment resulted in a decrease in the potency of the drug-dextran. Similar behavior was observed when increasing tumor loads were transplanted (10(5)-10(8) cells) and when the treatment was administered immediately. The most favorable effect of the drug-dextran was obtained with 10(7) cells, but against 10(8) cells neither the free drug nor the bound one was effective.

Animals↗
PubMed1977

Affinity labeling of human serum prealbumin with N-bromoacetyl-L-thyroxine.

Affinity labeling of human serum prealbumin with N-bromoacetyl-L-thyroxine (BrAcT4) was used to investigate the binding domain for L-thyroxine (T4) on prealbumin. Fluorescence titration with 8-anilinonaphthalene-1-sulfonate revealed a strong and a weak binding site for BrAcT4 (K1 = 1 X 10(8) M-1; K2 = 1 X 10(6) M-1). The reaction of BrAcT4 with prealbumin to form a covalent bond was inhibited in the presence of T4 and binding of T4 to prealbumin was nearly abolished after affinity labeling with BrAcT4. Affinity labeling with 2 mol of BrAcT4/mol of prealbumin resulted in covalent binding of 1 mol of ligand. Acid hydrolysis of affinity-labeled prealbumin gave Nepsilon-carboxymethyllysine and iminodiacetic acid, the latter being derived from the NH2-terminal glycine. A combination of analytical procedures, including tryptic digestion after maleylation, cyanogen bromide cleavage, digestion with yeast protease C, and sequential Edman degradations, revealed that the Nepsilon-carboxymethyllysine was derived from lysine-9 and lysine-15 and that the affinity label had distributed itself among glycine-1, lysine-9, and lysine-15 in a ratio of 29:63:8.

Affinity Labels↗
PubMed1977

Mapping of 23-S rRNA at the ribosomal peptidyl-transferase center by photo-affinity labeling.

Photo-sensitive peptidyl-tRNA's were used to scan the environment of the peptidyl-transferase center of the ribosome. The specificity of the previously described labeling in the 18-S fragment of 23-S rRNA by Boc-Phe(N3)-Phe-tRNA (4-azido-N-t-butoxycarbonyl-phenylalanyl-phenylalanyl-tRNA) was demonstrated by the ability of the covalently anchored molecule to serve as donor substrate in peptide bond formation. Labeling patterns were also obtained with Boc-Phe(N3)-Phe-Phe-tRNA bound at the acceptor site and with Boc-Phe(N3)-(Gly)n-Phe-tRNA (n = 2,4). The results indicate that subsequences within the 18-S fragment of 23-S rRNA are located close to the acceptor site as well as along the path where the peptide moiety adheres to the ribosome. Identification of the labeled sequences is expected to shed light on the spatial arrangement as well as functional role of rRNA in the peptidyl transferase center.

Acyltransferases↗