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Biomedical subjects

F T Liu

Publications and source records attributed to F T Liu.

At least 145 records · Page 8Linked to original sources
PubMed1980

Chemical synthesis of a polypeptide predicted from nucleotide sequence allows detection of a new retroviral gene product.

We previously determined the nucleotide sequence of the 3' end of Moloney leukaemia virus and discovered the potential coding region for an unknown protein, R. We now show that this region does encode a protein. A pentadecapeptide of R was chemically synthesized and antibodies raised against it. Antisera to the synthetic peptide recognize the R protein and the env precursor polyprotein in infected cells. The strategy presented here should provide a general method for accessing proteins predicted by nucleotide sequences.

Amino Acid Sequence↗
PubMed1980

Induction of immunologic tolerance to the trimellitate haptenic group in mice: model for a therapeutic approach to trimellitic anhydride-induced hypersensitivity syndromes in humans?

IgE and IgG antibody responses to the trimellitate (TM) hapten group were elicited in mice by the intraperitoneal injection of the hapten coupled with keyhole limpet hemocyanin (KLH). Treatment of such previously sensitized mice with the same hapten coupled to synthetic copolymer of D-glutamic acid and D-lysine (D-GL) after primary immunization resulted in significant and specific suppression of anti-TM antibody responses in both IgE and IgG classes. These results provide direct evidence for the potential clinical usefulness of the D-GL immunotherapeutic approach to TMA sensitivity in humans.

Animals↗
PubMed1979

Immunological tolerance to allergenic protein determinants: a therapeutic approach for selective inhibition of IgE antibody production.

Administration of stable conjugates prepared by coupling protein antigens such as ovalbumin or antigen E of ragweed extract to the synthetic random copolymer of D-glutamic acid and D-lysine (D-GL) is effective in inducing a state of long-lasting, antigen-specific immunological tolerance in experimental animals. A striking aspect of the tolerance induced by protein-D-GL conjugates is the remarkable selectivity of the tolerance for antibody responses of the IgE class. Protein-D-GL conjugates of either type were capable of inducing such tolerance both in unsensitized and in previously sensitized animals when administered in appropriate doses. Comparable doses of unconjugated proteins were likewise capable of suppressing IgE antibody production, although the duration of suppression in these cases was significantly less than that observed with protein-D-GL conjugates. If such conjugates act in man as they do in experimental animals, they could be of great value as therapeutic agents in selectively diminishing IgE antibody production while sparing antibody production in the IgG class.

Animals↗
PubMed1979

Immunologic tolerance to allergenic protein determinants: properties of tolerance induced in mice treated with conjugates of protein and a synthetic copolymer of D-glutamic acid and D-lysine (D-GL).

Conjugates of proteins and the synthetic copolymer of D-glutamic acid and D-lysine (protein-D-GL) reproducibly induce significant unresponsiveness to the protein antigens in experimental mice. Proteins studied include ovalbumin and antigen E of ragweed extract, the major allergen of ragweed pollen. The unresponsive state 1) can be induced in both unsensitized and previously sensitized experimental animals, 2) is selectively confined to responses of the IgE antibody class, 3) is long lasting, and 4) is highly antigen specific. IgE antibody responses can also be suppressed by administering comparable doses of unconjugated protein alone; however, the unresponsive state induced in this manner is only transient and rebound production of IgE antibody is often observed. Results from the studies of the cellular basis of the protein-D-GL induced unresponsiveness demonstrate that 1) protein-D-GL conjugates do not induce unresponsiveness at the level of protein-specific B cells, 2) tolerance is not induced by virtue of a detectable antigen-specific suppressor T cell mechanism, 3) tolerance is most probably induced in the antigen-specific helper T cell populations. The significant IgE-selective and antigen-specific tolerogenic activity of protein-D-GL conjugates make these compounds potential candidates for use as therapeutic agents in the treatment of IgE-mediated human allergic disorders induced by protein allergens.

Allergens↗
PubMed1978

Photochemistry of cytosine derivatives. 1. Photochemistry of thymidylyl-(3' leads to 5')-deoxycytidine.

The photochemistry of thymidylyl-(3' leads to 5')- deoxycytidine (dTpdC) was studied as a model system of adjacent thymine and cytosine bases in DNA. Acetophenonesensitized irradiation causes the cytosine moiety in dTpdC to react with the thymine moiety intramolecularly. Three unstable photoproducts are formed initially which are converted into three isomeric dinucleoside phosphates of thymine-uracil cyclobutane photodimer in a ratio of 4.2:2.2:1. Under the same irradiation condition thymidylyl-(3' leads to 5')-thymidine (dTpdT) yields two products in a ratio of 6:1. The structures of these products are established by chemical and spectroscopic methods. The major product in these reactions has been identified as the stereoisomer which has the same anti,anti relationship between the pyrimidine rings and the deoxyribose group as in the parent dinucleoside phosphates. The efficiency of the intramolecular dimerization of dTpdC is about one-third that of dTpdT. The results suggest that the cytosine base in DNA may be converted to a uracil base via photodimerization with an adjacent pyrimidine base, hydrolysis, and photoreactivation.

Deoxycytidine↗
PubMed1978

Photochemistry of cytosine derivatives. 2. Photohydration of cytosine derivatives. Proton magnetic resonance study on the chemical structure and property of photohydrates.

Photohydrates of cytidine and cytidylic acids have been definitively characterized to be isomeric 6-hydroxy-5,6-dihydrocytosine derivatives. It has also been demonstrated by nuclear magnetic resonance spectroscopy that (1) the stereochemistry of photohydration is random, (2) the C5-H trans to the C6-OH undergoes a rapid selective exchange in the presence of proton acids, and (3) the dehydration of photohydrates is a trans-elimination. The mechanism of these processes is discussed.

Cytidine↗
PubMed1978

Fluorescent photoaffinity labeling: adenosine 3',5'-cyclic monophosphate receptor sites.

An approach to the study of protein receptor sites in protein mixtures or supramolecular assemblies by using fluorescence spectroscopy is described. This approach, fluorescent photoaffinity labeling, combines the merits of photoaffinity labeling to attain site-directed reactivity with the probing power of fluorescent ligands. A fluorescent photoaffinity label for cyclic AMP receptor sites of cyclic AMP-dependent protein kinases was synthesized in both unlabeled and radioactive forms. The probe, 8-azido-1,N(6)-ethenoadenosine 3',5'-cyclic monophosphate, mimics cyclic AMP in its ability to stimulate the phosphotransferase activity of the protein kinases and strongly competes with cyclic AMP for its binding sites in all preparations so far tested. Photolysis, after equilibration of protein kinase and 8-azido-1,N(6)-ethenoadenosine 3',5'-cyclic monophosphate in the dark, effects binding of the intermediate nitrene irreversibly and specifically to the cyclic AMP sites with the development of fluorescence. Excess reagent and low molecular weight photolytic products are removable by dialysis. Studies of a crude beef heart preparation containing cyclic AMP-dependent protein kinase suggest that the cyclic AMP binding sites are hydrophobic in nature and strongly immobilize the adenine moiety of the cyclic nucleotide.

Affinity Labels↗