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T Y Liu

Publications and source records attributed to T Y Liu.

At least 145 records · Page 8Linked to original sources
PubMed1982

Quantitation of lipophilic chloroethylnitrosourea cancer chemotherapeutic agents.

A simple and rapid quantitative method for the derivatization and determination of lipophilic chloroethylnitrosoureas is described. This procedure involves the ether extraction of the chloroethylnitrosourea from plasma and conversion of the parent drug to an O-methylcarbamate by reaction in anhydrous methanol. The product O-methylcarbamate may be separated with gas chromatography (GC) and detected with nitrogen-specific GC detectors or with mass spectrometry using multiple-ion detection. The lower limit of detection for each method was approximately 100 ng/ml plasma.

Animals↗
PubMed1982

Micro-analysis of amino acids.

An automated amino acid analyzer has been developed for the analysis of amino acids with the sensitivity at the 10-100 pmol level except for proline which requires greater than 50 pmol. omicron-Phthalaldehyde, in the presence of 2-mercaptoethanol, is used for the fluorometric detection of amino groups (Roth, M. (1971) Anal. Chem. 43, 880-882). A post-column reaction of the amino acid with sodium hypochlorite (Bohlen, P. and Mellet, M. (1979) Anal. Biochem. 94, 313-321) gives oxidation products amenable to detection with omicron-phthalaldehyde. The instrument uses high-performance liquid chromatographic pumps capable of micro-flow rates with a minimum pulsation. The method is suitable for routine analyses of amino acids at picomole levels with reproducibility and accuracy comparable to the ninhydrin-based amino acid analysis.

Amino Acids↗
PubMed1982

Binding of C-reactive protein to C-carbohydrate and PC-substituted protein.

Human CRP and the CRPs of other species bind Ca2+ ion. After binding of the divalent cation, CRP binds all phosphate monoesters with a stochiometry of one mole per mole of CRP subunit. Replacement of the phosphate monoester group by other acidic groups or by conversion to a phosphodiester markedly diminishes or abolishes the ability to bind. Phosphorylcholine is bound by CRP with much higher affinity than other phosphate monoesters speaking for a second binding site with specificity for the positively charged trimethylammonium group. The distance separating the phosphate from the positively charged group may be relevant. Protein that has been coupled with phosphorylcholine or phosphorylethanolamine is able to precipitate with CRP. Several natural substances including pneumococcal-C polysaccharide which react with CRP have been found to contain phosphorylcholine. In addition CRP has another binding site accounting for its ability to react with depyruvylated type 4 pneumococcal polysaccharide which does not contain phosphate or choline.

Animals↗
PubMed1981

Lipid on capsular polysaccharides of gram-negative bacteria.

Hydrolysis of the meningococcal group A, B, and C, and Escherichia coli K92 polysaccharides by 60% aqueous hydrofluoric acid liberated various 1,2-diacylglycerols. These were extracted with chloroform, trimethylsilylated, and analyzed by gas chromatography-mass spectrometry. Two 1,2-diacylglycerols were the major components isolated. In each polysaccharide, 80 to 90% dipalmitoyl glycerol and 10 to 20% distearoyl glycerol were identified. No monoacylglycerols or mixed diacylglycerols were noted. The presence of the hydrophobic end causes the polysaccharides to aggregate in a micellar form and may be the entity by which the polysaccharide remains attached to the outer membrane of the bacterium giving rise to the structure recognized as a capsule.

Diglycerides↗
PubMed1981

Studies on Limulus amoebocyte. Isolation and identification of a membrane-bound protein activator of cyclic nucleotide phosphodiesterase from Limulus amoebocyte.

A protein isolated from Limulus polyphemus amoebocyte activates the hydrolysis of cyclic AMP by phosphodiesterase. The protein activator, like calmodulin, requires Ca2+ for its activity and is antagonized by calmodulin-modulating protein from bovine brain. 2-Chloro-10-(3-aminopropyl)-phenothiazine, a compound known to bind calmodulin, also inhibits the effect of the protein activator. This Limulus protein activator is an acidic protein with high percentage of glutamate and aspartate; it contains trimethyllysine, a characteristic amino acid found in all calmodulin. It is different from calmodulin isolated from other species, however, in its molecular weight (4 to 5 times greater), amino acid composition, antigenicity, and binding ability on 2-chloro-10-(3-aminopropyl)-phenothiazine affinity column chromatography. The amino acid composition, gel electrophoresis pattern, and molecular weight of this protein activator are indistinguishable from endotoxin-binding protein which we isolated previously by other independent methods. Immunologic studies demonstrate that these two proteins are essentially identical. The endotoxin-binding protein thus has the dual functions of binding endotoxin, and showing calmodulin-like activity. It may play an important role in degranulation of Limulus amoebocytes which is induced by minute amounts of gram-negative bacterial endotoxin.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1980

Composition and subunit structure of the cell receptor for immunoglobulin E.

The principal surface glycoprotein which specifically binds immunoglobulin E was isolated from rat basophilic leukemia cells in sufficient amounts for compositional and end group analyses. The protein has about 30% carbohydrate and a relatively low content of hydrophobic amino acid residues. No NH2-terminal residue was found by standard methods. The data suggest a Mr approximately equal to 50,000. The latter value is calculated on the basis of 1 molecule of receptor binding 1 molecule of immunoglobulin E. New data confirmed this valence. We propose a provisional model in which the principal component which binds immunoglobulin E is a monomer which, in cells and in nondenaturing solvents, is associated in a 1:1 ratio with the polypeptide of Mr approximately equal to 30,000 recently defined by studies employing cross-linking reagents.

Amino Acids↗
PubMed1980

The significance of 5'-nucleotide phosphodiesterase isozymes in the diagnosis of liver carcinoma.

The results of determination of the serum 5'-NPDase isozymes in 95 cases of primary liver carcinoma and other kinds of disease are presented. The 5'-NPDase-V was positive in 83.2% of primary liver cancer cases. This test might be a useful supplement to AFP determination, especially in AFP-negative liver cancer patients. In most patients who had undergone successful liver resection for primary carcinoma, the test became negative. A positive 5'NPDase-V test in patients with cancer elsewhere in the body may suggest liver metastasis. In addition, this test may be of some help in the differentiation of primary liver cancer from other kinds of liver disease. The problem of "false-positive" results of this test is discussed.

Diagnosis, Differential↗
PubMed1980

Studies on Limulus amoebocyte lysate. III. Purification of an endotoxin-binding protein from Limulus amoebocyte membranes.

A protein that has been isolated from Limulus polyphemus amoebocyte membranes binds endotoxin. The protein was purified by two independent methods, organic solvent extraction and affinity chromatography, both followed by gel filtration. Immunologic studies confirm that the protein is a component of amoebocyte membranes. Although without enzymatic activity, the binding protein enhances Limulus lysate gelation. As a membrane-associated endotoxin binding "protein," it may be involved in Limulus lysate coagulation, which is initiated by minute amounts of Gram-negative bacterial endotoxin. The protein has an apparent molecular weight of 80,000.

Amino Acids↗
PubMed1980

Protein mediated chemical reactions of chloroethylnitrosoureas.

The rates of chemical degradation of chloroethylnitrosoureas in serum are significantly higher than in aqueous buffer at the same pH and temperature. This rate enhancement is shown to be produced by a non-specific protein mediated chemical reaction that involves the formation of a protein-chloroethylnitrosourea (CENU) complex. Purified human serum albumin catalyzed reactions have been studied and Vm- and Km-values obtained for 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), and 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (MeCCNU). The rate of 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-1-nitrosourea (PCNU) decomposition is not enhanced by serum proteins. Formation of a protein-BCNU complex can be inhibited by salicylic acid and dodecanoic acid, two compounds that have a high albumin binding affinity. Reaction product analysis indicates that the only BCNU reaction catalyzed by albumin is conversion to active 2-chloroethylazohydroxide and 2-chloroethylisocyanate intermediates. Formation of these reactive species at the protein surface leads to a high proportion of covalent bond formation to the protein. These results emphasize the complex and structure specific factors that may affect the biodistribution, antitumor activity and toxicity of members of the chloroethylnitrosourea class of cancer chemotherapeutic agents.

Alkylating Agents↗
PubMed1979

Primary structure of human C-reactive protein.

The complete amino acid sequence has been derived for human C-reactive protein (CRP). The protein yielded a unique sequence containing 187 amino acids in a single polypeptide chain. The NH2-terminal residue of CRP is pyrrolidonecarboxylic acid and the COOH terminus is proline. The 2 half-cystine residues at positions 36 and 78 are involved in a disulfide bond. Based on the amino acid composition derived from the sequence data, a minimal molecular weight of 20,946 has been calculated for human CRP. This value agrees well with the molecular weight of 21,500 established by gel filtration of CRP in 5.0 M guanidine Cl (Gotschlich, E.C., and Edelman, G.M. (1965) Proc. Natl. Acad. Sci. U.S.A. 54, 558--566). The primary structure of human CRP has been examined for internal homology and compared to all known proteins whose structures were published before April, 1978 by two computer programs; program SEARCH and program RELATE (Dayhoff, M. O., ed (1976) in Atlas of Protein Sequence and Structure, Vol. 5, Suppl. 2, pp. 3--8, National Biomedical Research Foundation, Silver Spring, MD). The computer analyses showed no significant repeating sequences within the C-reactive protein molecule. This observation seems to rule out the possibility of gene duplication in the evolution of this protein. Distant homologies, which were statistically insignificant, have been noted to the CH2 domain of immunoglobulin G (IgG) and to C3a anaphylotoxin. The homologie noted are insufficient to support a common evolutionary origin of these proteins. No homology region in other heavy chains was observed. It is therefore preferable, at this point in time, to assign CRP and the protein known as 9.5 S alpha-glycoprotein, P component, and Clt to a new super family unrelated to any other proteins investigated. The homology between these proteins was demonstrated previously (Osmand, A.P., Friedenson, B., Gewurz, H., Painter, R.H., Hofmann, T., and Shelton, E. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 739--743) on the basis of sequence data on approximately 20 NH2-terminal residues of rabbit C-reactive protein, of Clt, and a cyanogen bromide fragment of human CRP.

Amino Acid Sequence↗
PubMed1978

Cell-free biosynthesis of the O-acetylated N-acetylneuraminic acid capsular polysaccharide of group C meningococci.

A cell-free system was established to study the biosynthesis of group C meningococcal capsular polysaccharide, an alpha-2 leads to 9-linked N-acetylneuraminic acid (NeuAc) homopolymer containing O-acetyl groups at either C7 or C8. Sialyltransferase activity, isolated from group C meningococcus strain C-11, catalyzed incorporation of [14C]NeuAc from CMP (CMP--[14C]NeuAc) into polymeric form. This sialyltransferase was stimulated by addition of meningococcus group C and Escherichia coli K92 capsular polysaccharides, the latter being an alpha-2 leads to 8- and alpha-2 leads to 9-linked NeuAc heteropolymer. Group C meningococcal sialyltransferase did not require divalent ions but was stimulated by Mn2+. Attempts to demonstrate a lipid-soluble intermediate in the biosynthesis of this NeuAc polymer were unsuccessful. Meningococcal group C sialyltransferase incorporated NeuAc into a membrane-associated product. The polysaccharide can be extracted from the membrane-bound fraction with Triton X-100. The newly synthesized polysaccharide coprecipitates with authentic group C antigen in meningococcal group C antiserum and is degraded by sodium metaperiodate, indicating that the NeuAc polymer synthesized by the cell-free system consists of alpha-2 leads to 9 linkage. Meningococcal group C spheroplast membranes contain an O-acetylase that can catalyze the transfer of acetyl groups from acetyl coenzyme A to the in vitro-synthesized polysaccharide.

Acetylation↗
PubMed1977

Structural studies on the sialic acid polysaccharide antigen of Escherichia coli strain Bos-12.

A polysaccharide, antigenically related to group C meningococcus, has been isolated from Escherichia coli strain Bos-12 (016; K92; NM). Like groups B and C meningococcal polysaccharide, the Bos-12 antigen is a pure polymer of sialic acid. 13C NMR studies on the meningococcal group B and C polysaccharides have indicated that the former consists of sialic acid units linked 2 leads to 8- alpha, whereas the latter contains the sialic acid residues linked 2 leads to 9-alpha (Bhattacharjee, A.K., Jennings, H.J., Kenny, C.P., Martin, A., and Smith, I.C.P. (1975), J. Biol. Chem. 250, 1926). Comparison of natural abundance 13C NMR spectra of the Bos-12 polysaccharide with group B and C meningococcal polysaccharides established that Bos-12 was either (a) an equimolar mixture of 2 leads to 8-alpha linked sialic acid homopolymers or (b) a 2 leads to 8-alpha/2 leads to 9-alpha heteropolymer. These possibilities were distinguished in the following manner. The fact that Bos-12 polysaccharide precipitated with anti-group C serum but not with anti-group B serum would seem to exclude a. Further, chemical studies (periodate oxidation followed by tritiated NaBH4 reduction) gave saccharides with a radioactive-labeling pattern expected for alternating 2 leads to 8-alpha/2 leads to 9-alpha sialic acid linkages. Bos-12 is thus an 2 leads to 8/2 lead to 9-alpha heteropolymer.

Borohydrides↗