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Biomedical subjects

C W Chen

Publications and source records attributed to C W Chen.

At least 163 records · Page 9Linked to original sources
PubMed1985

Adaptive cellular response to hyperthermia: 31P-NMR studies.

Dynamic intracellular ATP and Pi levels were measured non-invasively for Chinese hamster V79 cells by 31P-NMR under conditions of thermotolerance and heat-shock protein induction. High densities of cells were embedded in agarose strands, placed within a standard NMR sample tube, and perfused with medium maintained either at 37 or 43 degrees C at pH 7.35. Cell survival and heat-shock protein synthesis were assessed either from parallel monolayer cultures or cells dislodged from the agarose strands post-treatment. Thermotolerance (heat resistance) and heat-shock protein synthesis was induced by a 1 h exposure to 43 degrees C followed by incubation for 5 h at 37 degrees C. After the 5 h incubation at 37 degrees C, marked thermal resistance was observed in regard to survival with concomitant synthesis of two major heat-shock proteins at 70 and 103 kDa. Studies were also conducted where tolerance and heat-shock protein synthesis were partially inhibited by depletion of cellular glutathione (GSH) prior to and during heat treatment. Dynamic measurement of intracellular ATP of cells heated with or without GSH depletion revealed no change in steady-state levels immediately after heating or during the 5 h post-heating incubation at 37 degrees C where thermotolerance and heat-shock proteins develop. These data are consistent with other reported data for mammalian cells and indicate that the steady-state ATP levels in mammalian cells remain unchanged during and after the acquisition of the thermotolerant state.

Adenosine Triphosphate↗
PubMed1985

Nuclear magnetic resonance and neutron diffraction studies of the complex of ribonuclease A with uridine vanadate, a transition-state analogue.

The complex of ribonuclease A (RNase A) with uridine vanadate (U-V), a transition-state analogue, has been studied with 51V and proton NMR spectroscopy in solution and by neutron diffraction in the crystalline state. Upon the addition of aliquots of U-V at pH 6.6, the C epsilon-H resonances of the two active-site histidine residues 119 and 12 decrease in intensity while four new resonances appear. Above pH 8 and below pH 5, these four resonances decrease in intensity as the complex dissociates. These four resonances are assigned to His-119 and His-12 in protonated and unprotonated forms in the RNase-U-V complex. These resonances do not titrate or change in relative area in the pH range 5-8, indicating a slow protonation process, and the extent of protonation remains constant with ca. 58% of His-12 and ca. 26% of His-119 being protonated. The results of diffraction studies show that both His-12 and His-119 occupy well-defined positions in the RNase-U-V complex and that both are protonated. However, while the classic interpretation of the mechanism of action of RNase based on the proposal of Findlay et al. [Findlay, D., Herries, D. G., Mathias, A. P., Rabin, B. R., & Ross, C. A. (1962) Biochem. J. 85, 152-153] requires both His-12 and His-119 to be in axial positions relative to the pentacoordinate transition state, in the diffraction structure His-12 is found to be in an equatorial position, while Lys-41 is close to an axial position. Hydrogen exchange data show that the mobility and accessibility of amides in the RNase-U-V complex do not significantly differ from what was observed in the native enzyme. The results of both proton NMR in solution and neutron diffraction in the crystal are compared and interpreted in terms of the mechanism of action of RNase.

Animals↗
PubMed1984

Metabolic studies of mammalian cells by 31P-NMR using a continuous perfusion technique.

Levels of ATP and Pi in metabolically active Chinese hamster lung fibroblasts were monitored noninvasively by 31P-NMR over many hours and under a variety of conditions. The cells were embedded in a matrix of agarose gel in the form of fine threads which were continuously perfused in a standard NMR tube. The small diameter of the thread allows rapid diffusion of metabolites and drugs into the cells. The changes in ATP and Pi levels were followed as a function of time in response to perfusion with a glucose-containing medium, with isotonic saline and with a medium containing 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation. This gel-thread perfusion method should enable routine NMR studies of cellular metabolism, and may have other potential biological applications.

2,4-Dinitrophenol↗
PubMed1984

Paramagnetic metalloporphyrins as potential contrast agents in NMR imaging.

Several water-soluble paramagnetic metalloporphyrins were found to increase significantly the relaxation rate (1/T1) of water. Such compounds are known to be selectively retained by tumors in animals, and consequently we identify them as potential contrast agents for tumors in NMR imaging.

Contrast Media↗
PubMed1984

Poly(d2NH2A-dT): effect of 2-amino substituent on the B to Z transition.

The effect of 2-amino substitution in adenosine (which permits formation of three hydrogen bonds to T) on the B to Z transition was examined in synthetic DNA of alternating purine-pyrimidine sequence. Results of CD, IR, and 31P NMR experiments show that (d2NH2A-dT)n undergoes a cooperative transition to a different helical structure under the same conditions as the B to Z transition of (dG-dC)n.

2-Aminopurine↗
PubMed1984

Molecular epidemiology of adenovirus type 8 (Ad 8) in Taiwan: four subtypes recovered during the period of 1980-1981 from patients with epidemic keratoconjunctivitis.

Adenovirus type 8 (Ad 8) has been the major and important causative agent of epidemic keratoconjunctivitis (EKC). By enzymatic cleavage analysis with five endonucleases, PstI, HindIII, BamHI, SalI and SstI, 27 out of 149 Ad 8 isolates recovered from patients with EKC during the period from July, 1980 to July, 1981 in Kaohsiung, Taiwan, were studied. By cleavage patterns, 27 Ad 8 isolates in Kaohsiung were classified into four subtypes which were found to be different from the subtypes (Ad 8A, Ad 8B) prevalent in Sapporo (1).

Adenoviruses, Human↗
PubMed1983

A rapid two-dimensional fractionation of DNA restriction fragments.

Genomic DNA that has been digested with a restriction endonuclease and fractionated by electrophoresis on an agarose gel can be recovered on glass-fiber filters by a new blotting scheme. The DNA fragments in each fraction are then digested with a second restriction nuclease and then separated on a slab gel, resulting in a two-dimensional display of the restriction fragments. This rapid fingerprinting technique is useful in the analysis of complex genomes and in the isolation and cloning of particular sequences.

Base Sequence↗
PubMed1983

Use of fiberoptic choledochoscope in common bile duct and intrahepatic duct exploration.

This report summarizes our experience with 339 consecutive flexible fiberoptic choledochoscopic examinations performed in the course of 598 common bile duct explorations for biliary tract stones. Routine choledochoscopy added 5 to 10 minutes to the operation and caused no complications. In 81 of the patients, additional stones were discovered with choledochofiberscopy after completion of routine bile duct exploration. Postoperative cholangiography demonstrated a retained stone in 57 patients (two in the common bile duct and 55 in the intrahepatic ducts). Forty-two patients with stones retained in the intrahepatic ducts were diagnosed during operation with the fiberoptic choledochoscope, but those stones were very difficult for us to remove. The accuracy of postexploratory choledochoscopy in diagnosis of stones in the common bile duct and intrahepatic ducts was 99.0% and 90.5%, respectively. Choledochofiberscopy is useful in exploration of the common bile duct and a safe procedure in the diagnosis of biliary tract stones during operation.

Bile Ducts, Intrahepatic↗