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Biomedical subjects

S J Li

Publications and source records attributed to S J Li.

At least 109 records · Page 6Linked to original sources
PubMed1986

Identification and assignment of base pairs in the "tuned helix" of intact and ribonuclease T1 cleavage fragments of wheat germ ribosomal 5S RNA via 500-MHz proton homonuclear Overhauser enhancements.

Wheat germ has been chosen as a representative eukaryote for study of ribosomal 5S RNA secondary structure. Proton homonuclear Overhauser enhancements (NOE's) at 500 MHz for the hydrogen-bonded base-pair protons in the 10-15 ppm region are used to establish the identity (A X U, G X C, or G X U) and base-pair sequence (e.g., G X C-A X U-C X G) within a given helical segment. Assignment of that segment to particular base pairs in the secondary structure is based upon NOE's conducted at different temperatures (to determine which signals "melt" together), variation of salt conditions (to produce differential chemical shifts in order to better distinguish components of an unresolved spectral envelope), and isolation and purification of RNase T1 cleavage fragments (in order to reduce the spectrum to just a few base pairs). The NOE patterns for the RNase T1 fragments are the same as in the intact 5S RNA, supporting the assumption that structural features of this region in the intact 5S RNA are preserved in the fragment. Chemical shifts predicted from ring current induced effects for a proposed base-pair sequence are then compared to experimental chemical shifts. By these methods, a portion of the "tuned helix" segment (namely, the base-pair sequence C18G60-A19U59-C20G58) is demonstrated spectroscopically for the first time in any 5S RNA. The tuned helix and common arm segments are less stable than the rest of the molecule. Variation of sodium and magnesium levels reveals multiple configurations of the wheat germ 5S RNA in solution.

Base Composition↗
PubMed1985

Multistage unfolding of wheat germ ribosomal 5S RNA analyzed by differential scanning calorimetry.

Unfolding of purified wheat germ ribosomal RNA has been studied by differential scanning calorimetry (DSC) from 15 to 95 degrees C, in the presence and absence of 100 mM NaCl and/or 10 mM MgCl2. The total enthalpy of melting varies from about 290 (no sodium or magnesium) to 480 kcal/mol (Mg2+ only) and precisely accounts for the number and types of base pairs deduced from prior Fourier-transform infrared experiments. The composite DSC curves are analyzed into four individual two-state melting stages. Both Na+ and Mg2+ shift the melting transitions to higher temperature; in addition, Mg2+ causes the individual transitions to merge (i.e., melt cooperatively) and leads to irreversible chain cleavage at high temperature. The results are analyzed according to three general secondary base-pairing models for eukaryotic 5S RNA.

Base Sequence↗
PubMed1984

Base pairing in wheat germ ribosomal 5S RNA as measured by ultraviolet absorption, circular dichroism, and Fourier-transform infrared spectrometry.

Ultraviolet absorption (UV) and circular dichroism (CD) spectra of wheat germ 5S RNA, when compared to tRNAPhe, indicate a largely base-paired and base-stacked helical structure, containing up to 36 base pairs. Fourier-transform infrared (FT-IR) spectra of tRNAPhe and wheat germ ribosomal 5S RNA have been acquired at 30 and 90 degrees C. From the difference of the FT-IR spectra between 90 and 30 degrees C, the number of base pairs in both RNAs was determined by modification of a previously published procedure [Burkey, K. O., Marshall, A. G., & Alben, J. O. (1983) Biochemistry 22, 4223-4229]. The base-pair composition and total base-pair number from FT-IR data are now consistent for the first time with optical (UV, CD, Raman) and NMR results for ribosomal 5S RNA. Without added Mg2+, tRNAPhe gave 18 +/- 2 base pairs [7 A-U and 11 G-C], in good agreement with the number of secondary base pairs from X-ray crystallography [8 A-U, 12 G-C, and 1 G-U]. Within the 10% precision of the FT-IR method, wheat germ 5S RNA exhibits essentially the same number of base pairs [14 A-U, 17 G-C, and 5 G-U; for a total of 36] in the absence of Mg2+ as in the presence of Mg2+ [14 A-U, 18 G-C, and 3 G-U; for a total of 35], in agreement with the UV hyperchromism estimate of G-C/(A-U + G-C) = 0.58.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Composition↗
PubMed1984

Preparative-scale isolation and purification of procaryotic and eucaryotic ribosomal 5 S RNA: Bacillus subtilis, Neurospora crassa, and wheat germ.

Ribosomal 5 S RNA from three different organisms has been isolated in high yield and purity. Without prior isolation of ribosomes, a presoak in buffer followed by phenol extraction, DE-32 ion-exchange chromatography, and Sephadex G-75 gel-permeation chromatography yields at least 5-10 mg of electrophoretically homogeneous 5 S RNA from 100 g of cells. Ribonuclease activity is eliminated by various combinations of low temperature, sodium dodecyl sulfate, phenol, and bentonite. High-molecular-weight contaminants are suppressed by either 65 degrees C heat treatment or lowered sodium dodecyl sulfate concentration. For the eucaryotes, 5.8 S RNA contamination is reduced either by low temperature in the initial solubilization or by postponing 65 degrees C heat treatment until after the phenol extraction step.

Bacillus subtilis↗
PubMed1984

Depressor and bradycardic effect following intrathecal injection of [NMePhe3,D-Pro4]morphiceptin in rats.

The intrathecal injection of 1.25, 2.5 and 5 micrograms of [ NMePhe3 ,D-Pro4] morphiceptin (MC), a highly selective mu receptor agonist, in pentobarbital-anesthetized rats resulted in a dose-dependent decrease of mean arterial pressure, reaching a maximal effect 1 h after its administration. A marked bradycardic effect paralleled the depressor effect. These effects were totally reversed by prior intrathecal injection of 10 micrograms of naloxone. The effect of MC was fully present in bilaterally vagotomized rats and in rats under artificial respiration. These results provide evidence for the opioid control of blood pressure and heart rate via mu receptors in the spinal cord.

Animals↗
PubMed1983

Efficacy of polyglycolic acid (Dexon) microsutures in peripheral nerve anastomoses in the rat: 1. Epineural suture.

The efficacy of polyglycolic acid (Dexon) microsuture in peripheral nerve repair was studied using 84 and 28 reanastomoses of freshly severed rat sciatic nerve employing Dexon and nylon 9-0 interrupted epineural suture technique. Animals were sacrificed and sutured portions of the nerves were histologically examined. There were almost identical suture reactions by day 7, except that the intensity of polymorphonuclear (PMN) and macrophage infiltrate in the nylon-sutured nerves was far greater than in the Dexon-sutured group. Although the intensity of the nylon-suture reaction subsided considerably after day 21, the lymphocytes, macrophages, and plasma cells surrounded the suture as long as the sutures remained in the nerves up to 12 months postoperatively. The Dexon-sutured nerve segments showed disappearance of the inflammatory cells as soon as the sutures were completely absorbed. The Dexon sutures were still detectable at months 1 and 2 but not after month 3.

Animals↗
PubMed1982

Vasovasostomy in the rat. Improved technique using absorbable microsuture (polyglycolic acid).

An improved technique for vasovasostomy in the rat is presented. To eliminate the suture crowds that could cause obstruction of the vasal lumen, one deep raw suture technique had been employed using polyglycolic acid (Dexon) microsuture. A total of 62 vasal anastomoses in 48 male Lewis rats was performed, and follow-up to twelve months found no disruption or constriction at the anastomoses. Despite occasional sperm granuloma formation at the anastomotic sites, all anastomoses demonstrated patency. Dexon appears to be suitable for genitourinary tract surgery, at least, in the rat.

Animals↗
PubMed1982

The implication of central serotonin in electro-acupuncture tolerance in the rat.

Electro-acupuncture (EA) applied to both legs for 30 min raised the tail flick latency of the rat significantly. This effect of EA analgesia became attenuated and finally disappeared after repeated EA stimulations, which was termed EA tolerance. EA tolerance and its cross tolerance to morphine analgesia were found to be partially reversed by intracerebro-ventricular injection of 5-hydroxytryptophan (5-HTP), the precursor of 5-hydroxytryptamine (5-HT). However, there was no depletion in cerebral 5-HT, nor was there decrease of the number of 5-HT receptors in the brain of the EA tolerant animals. Results obtained from different lines of analysis point to the conclusion that development of tolerance to profoundly released 5-HT during prolonged EA stimulation may constitute one of the mechanisms for EA tolerance.

5-Hydroxytryptophan↗
PubMed1981

Partial splenectomy with CO2 laser: an experimental study.

A freehand carbon dioxide laser is now available for surgical procedures. A comparison of its utility with the electrocautery was carried out in five dogs by the performance of hemisplenectomy. All dogs survived without complications. The laser proved to be an effective instrument for partial splenectomy under the terms of the experiment.

Animals↗