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D C Yang

Publications and source records attributed to D C Yang.

At least 91 records · Page 5Linked to original sources
PubMed1981

Mitogenicity and binding properties of beta-galactoside-binding lectin from chick-embryo kidney.

THe beta-galactoside-binding lectin binds to glucosamine, mannosamine and galactosamine in addition to beta-galactoside, as determined by the inhibition of haemagglutination. Haemagglutination is further extended to examine the interaction of the binding sites for hexosamines and beta-galactosides, indicating that the binding of hexosamine and beta-galactoside is competitive. The lectin also shows strong mitogenic activity toward lymphocytes from mouse lymph node, as determined by the stimulation of thymidine incorporation.

Animals↗
PubMed1981

Some analogues of luteinizing hormone-releasing hormone with substituents in position 10.

As part of our studies on the design of agonists of the luteinizing hormone-releasing hormone (LH-RH), we have synthesized the [des-Gly-NH2(10)]-LH-RH N-methylhydrazide (1), the corresponding thiosemicarbazide (2), and the N-formyl- (3) N-acetyl- (4) and N-(trifluoroacetyl)hydrazide (5). Analogue 1 may be regarded as isosteric with [des-Gly-NH2(10)]-LH-RH N-alkylamides which are, in general, potent agonists. Analogues 2-5 may be regarded as isosteric with [aza-Gly-NH2(10)]-OH-RH, which is equipotent with the hormone. The required protected intermediates were prepared by solid-phase synthesis, and the free peptides were prepared from them by deprotection with HF, followed by purification on Sephadex G-25. Bioassay of these analogues with rat hemipituitaries in vitro showed the following values as percentages of the hormonal values for the release of LH and FSH respectively: N-methylhydrazide (1), 17 and 11%; semithiocarbazide (2), 6.5 and 4.6%; N-formylhydrazide (3), 15.3 and 10%; N-acetylhydrazide (4), 1.2 and 0.6%; N-(trifluoroacetyl)hydrazide (5), 1.0 and 0.9%. Thus, these types of isosteric substitutions are inimical to the preservation of the high biological activity of LH-RH.

Animals↗
PubMed1981

An approach to the elucidation of metabolic breakdown products of the luteinizing hormone-releasing hormone.

Metabolic breakdown of the luteinizing hormone-releasing hormone (LH-RH) could lead to the following fragments containing pyroglutamic acid: pyroglutamic acid (1), pGlu-His (2), pGLu-His-Trp (3), pGlu-His-Trp-Ser (4), etc., and finally pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly (10). We have synthesized fragments 2-10 and successfully separated all ten metabolites and LH-RH by high-performance liquid chromatography (HPLC) with a muBondapak C18 column. In a test of the viability of the method, cochromatography of fragments 1-10 and LH-RH with the products of chymotryptic digestion of tritiated LH-RH showed radioactive peaks corresponding to the expected products, fragments 3 and 5. Analysis of the products of incubation of a rat kidney homogenate supernatant with LH-RH showed fragments 1-4 and LH-RH. The finding of breakdown at position 4 uncovers a new site of LH-RH breakdown and points the way to the design of potential LH-RH antagonists and agonists where the 4 position would be substituted with unnatural amino acids to prevent breakdown.

Animals↗
PubMed1981

Stoichiometry and composition of an aminoacyl-tRNA synthetase complex from rat liver.

The particulate aminoacyl-tRNA synthetases of rat liver were copurified about 1000-fold with more than 20% yields for individual synthetase activities. Measurements of aminoacylation activities showed that lysyl-, arginyl-, leucyl-, isoleucyl-, and methionyl-tRNA synthetases in the purified complex cosedimented at 18 S. The molecular weight of the synthetase complex is about one million, as estimated by gel filtration. The stoichiometry of the synthetase in the complex was determined by active site titration with aminoacyl adenylates. Results indicate that the 18S synthetase complex contains one subunit of methionyl-tRNA synthetase and two subunits of lysyl-tRNA synthetase. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed that the 18S synthetase complex contains eight major protein bands. Proteins with subunit molecular weights of 104,000, 92,000, 69,000, and 67,000 are present in molar ratios of 1:1:2:2, while proteins with subunit molecular weights of amounts. These results suggest that the particulate aminoacyl-tRNA synthetases exist as a heterotypic multienzyme complex with defined structure.

Amino Acyl-tRNA Synthetases↗
PubMed1980

Purification and characterization of lysyl-tRNA synthetase after dissociation of the particulate aminoacyl-tRNA synthetases from rat liver.

The major aminoacyl-tRNA synthetase complex (the 24 S complex) isolated from rat liver, which contains lysyl-, leucyl-, and arginyl-tRNA synthetase activities, is dissociated into fully active free aminoacyl-tRNA synthetases by column chromatography on diaminooctyl-Sepharose. During the hydrophobic interaction chromatography, more than a quantitative yield of the lysyl-tRNA synthetase activity is obtained. The free lysyl-tRNA synthetase, dissociated from the synthetase complex, is purified about 2,000-fold with a 13% yield by conventional column chromatography. Lysyl-tRNA synthetase is also purified from the 24 S synthetase complex by affinity column chromatography on lysyl-diaminohexyl-Sepharose. Free lysyl-tRNA synthetase as dissociated from the synthetase complex, is evidently a dimeric enzyme with a subunit molecular weight of 66,000 +/- 3,000, as determined by gel electrophoresis, sucrose gradient centrifugation and gel filtration.

Amino Acyl-tRNA Synthetases↗
PubMed1979

Disassembly and gross structure of particulate aminoacyl-tRNA synthetases from rat liver. Isolation and the structural relationship of synthetase complexes.

The major high molecular weight complex of aminoacyl-tRNA synthetases is purified about 1000-fold with 30% yield from rat liver. The synthetase complex sediments at 24 S with a molecular weight of 900,000 +/- 75,000 and contains aminoacylation activities for lysine, arginine, isoleucine, leucine, methionine, glutamine, glutamate, and proline. The 24 S synthetase complex dissociates into 21 S, 18 S, 13 S, 12 S, and 10 S complexes with specific enzymatic activities. Dissociation of the 24 S complex into active free synthetases is achieved by hydrophobic interaction chromatography. The disassembly of the synthetase complex is consistent with the structural model of a heterotypic multienzyme complex and suggests that the complex formation is due to the specific intermolecular interactions among the synthetases.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Adenosine cyclic 3',5'-monophosphate-dependent protein kinase from human platelets.

A single cyclic AMP-dependent protein kinase (EC 2.7.1.37) has been isolated from human platelets by using DEAE-cellulose ion-exchange chromatography and Sephadex G-150 gel filtration. The molecular weight of the protein kinase was estimated to be 86 490. In the presence of cyclic AMP, the protein kinase could be dissociated into a catalytic subunit of molecular weight 50 000, and either one regulatory subunit of molecular weight 110 000 or two regulatory subunits of molecular weights 110 000 and 38 100, depending on the pH used. Recombination of either of the regulatory subunits with the catalytic subunit restored cyclic AMP-dependency in the catalytic subunit. The apparent Km for ATP in the presence of 10 muM Mg2+ was 4 muM (plus cyclic AMP) and 4.3 muM (minus cyclic AMP). The concentration of cyclic AMP needed for half-maximal stimulation of the protein kinase was 0.172 muM and apparent dissociation constants of 3.7 nM (absence of MgATP) and 0.18 muM (presence of MgATP) were exhibited by the "protein kinase-cyclic AMP complex". The enzyme required Mg2+ for maximum activity and showed a pH optimum of 6.2 with histone as substrate. In addition to four major endogenous platelet protein acceptors of apparent molecular weights 45 000, 28000, 18 500, and 11 100, the platelet protein kinase also phosphorylated the exogenous acceptor proteins thrombin, collagen and histone, all capable of inducing platelet aggregation. Prothrombin, a nonaggregating agent, was not phosphorylated.

Binding Sites↗
PubMedDate not supplied

Role of CT in left-sided acute appendicitis: case report.

We present the computed tomographic findings in a case of left-sided acute appendicitis associated with midgut malrotation, which is a rare anomaly. The inflamed appendix was visualized as a tubular, fluid-filled, enhancing structure in the left lower quadrant. The entire colon was located in the left abdomen. The presence of a superior mesenteric vein rotation sign ascertained the presence of midgut malrotation. Computed tomography is useful not only in providing accurate diagnosis of left-sided appendicitis but also in detecting associated rotational anomalies, which may require separate surgical correction.

Appendicitis↗