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Biomedical subjects

D H Chen

Publications and source records attributed to D H Chen.

At least 55 records · Page 3Linked to original sources
PubMed1983

Synthesis of the 5'-half molecule of yeast alanine tRNA.

In this paper, we report the synthesis of the 5'-half molecule of yeast alanine tRNA (tRNAAlay) by ligating three oligonucleotide fragments corresponding to the nucleotide sequences 1-13, 14-22 and 23-35 respectively under the catalysis of T4 RNA ligase (Fig. 1). Because of the high purity of the oligonucleotide fragments and the excellent quality of T4RNA ligase and polynucleotide kinase we prepared, the isolation steps were simplified and the overall yields were much higher. The ligating yield of the docosamer (IV) was 75%, that of the pentatriacontamer (V), 90%, and the isolated yield of the final product was 21% calculated on the basis of the tridecamer (III) used in the first reaction. Under the action of T4 RNA ligase the synthetic 5'-half molecule was joined with the natural 3'-half molecule forming a semi-synthetic tRNAAlay, which possessed the biological activities of both accepting (3H)-alanine and incorporating it into proteins. The correctness of the structure of the synthetic 5'-half molecule was verified by both chemical analysis and biological activity assay.

Base Sequence↗
PubMed1978

Qualitative and quantitative study of synaptic displacement in chromatolyzed spinal motoneurons of the cat.

Qualitative and quantitative cytological evidences show a reduction in number and percentage of coverage of terminals on chromatolyzed spinal motoneurons 4 to 90 days after severance of their axons in the ventral root. The reduction in number and percentage of boutons on the surface membrane is due to detachment of synapses. This detachment is associated with changes in specialized regions (synaptic complexes: Conradi, '69) of synapses which involve disappearance of both pre-and postsynaptic membrane thickenings and widening of the synaptic cleft (width of 400-1,400 A). The separation of terminals from surface membrane is also associated with the presence of reactive astrocytes and microglia. Most areas of surface membrane bared of synaptic contact are occupied by astrocytic processes. The astroglial responses coincide with the loss of synapses. Microglial cells, although extending to neuronal surface membrane, cover only a small portion of it. An extensive separation of boutons by microglia is not observed. Most microglia are seen located at some distance from surface membrane and are frequently separated by sheets of astrocytic processes. Synaptic restoration occurs by about 90 days after axotomy. Some motoneurons show good recovery, while others show only a limited amount.

Animals↗
PubMed1977

Immunity to sporozoite-induced malaria infeciton in mice. I. The effect of immunization of T and B cell-deficient mice.

The cellular basis of immunity to sporozoites was investigated by examing the effect of immunization of T and B cell-deficient C57BL/6N X BALB/c AnN F1 (BLCF1) mice compared to immunocompetent controls. Immunization of T cell-deficient (ATX-BM-ATS) BLCF1 mice with x-irradiated sporozoites did not result in the generation of protective immunity. The same immunization protocols protected all immunocompetent controls. In contrast, B cell-deficient (micron-suppressed) BLCF1 mice were protected by immunization in the majority of cases. The absence of detectable serum circumsporozoite precipitins or sporozoite neutralizing activity in the micron-suppressed mice that resisted a sporozoite challenge suggests a minor role for these humoral factors in protection. These data demonstrate a preeminent role for T cells in the induction of protective immunity in BLCF 1 mice against a P. berghei sporozoite infection.

Animals↗