Biomedical subjects

T E Chang

Publications and source records attributed to T E Chang.

5 recordsLinked to original sources

PubMed2001

Circulating hepatitis B virus nucleic acids in chronic infection : representation of differently polyadenylated viral transcripts during progression to nonreplicative stages.

PURPOSE: Beside the established maturation of hepatitis B virus (HBV) transcripts at a polyadenylation signal downstream of the HBV x protein open reading frame, maturation at an internal polyadenylation signal has been observed in the chronically infected liver. In the present study, it was the aim to identify the respective circulating full-length and truncated transcripts in plasma/serum of carriers. EXPERIMENTAL DESIGN: Nucleic acids extracted from sera were analyzed using established PCR and reverse transcription-PCR procedures targeted to HBV x protein gene regions. Amplification products were cloned and sequenced. RESULTS: Base substitution patterns were determined, which indicated infection stages advanced to different degrees regardless of the transcript type analyzed. HBV full-length RNA (fRNA) showed a high correlation with hepatitis B e antigen and viral DNA, indicative for a replicative infection. In contrast, truncated RNA (trRNA) appeared to be independent of hepatitis B e antigen and showed only a weak association with circulating viral DNA. No correlation was observed between the levels of trRNA and the apparent liver damage as reflected by alanine transaminase levels. An age-dependent representation of fRNA and trRNA was observed: fRNA decreased progressively to low levels, whereas trRNA remained at comparably high values. trRNA and RNA not polyadenylated at either of the two polyadenylation signals were detected even in the absence of any other conventional HBV seromarker, including viral DNA. This was shown for patients with cryptogenic cirrhosis and hepatitis C virus carriers. CONCLUSIONS: The identification of HBV RNA in human serum has a diagnostic potential for apparent and for inapparent infection stages.

Adolescent↗

PubMed1990

Purification and Characterization of Glutamyl-tRNA Synthetase : An Enzyme Involved in Chlorophyll Biosynthesis.

Chlorophyll biosynthesis starts with the synthesis of glutamyl-tRNA (glu-tRNA) by a glutamyl-tRNA synthetase (Glu RS). The glu-tRNA is subsequently transformed to delta-aminolevulinic acid (ALA), which is a committed and regulated precursor in the chlorophyll biosynthetic pathway. The Glu RS from a green alga, Chlamydomonas reinhardtii, was purified and shown to be able to synthesize glu-tRNA and to participate in ALA synthesis in a coupled enzyme assay. Physical and chemical characterization of the purified Glu RS indicated that the enzyme had been purified to homogeneity. The purified enzyme has a native molecular weight of 60,000, an isoelectric point of 4.6, and it formed a single band of 32,500 daltons when analyzed by a silver stained denaturing gel. The N-terminal amino acid sequence of the 32,500 dalton protein was determined to be Asn-Lys-Val-Ala-Leu-Leu-Gly-Ala-Ala-Gly. The molecular weight analyses together with the unambiguous N-terminal amino acid sequence obtained from the purified enzyme suggested that the native enzyme was composed of two identical subunits. Polyclonal antibodies raised against the purified and denatured enzyme were able to inhibit the activity of the native enzyme and to interact specifically with the 32,500 dalton band on Western blots. Thus, the antibodies provided an additional linkage for the structural and functional identities of the enzyme. In vitro experiments showed that over 90% of the glu RS activity was inhibited by 5 micromolar heme, which suggested that Glu RS may be a regulated enzyme in the chlorophyll biosynthetic pathway.

Journal Article↗

PubMed1990

Ultrasonographic demonstration of duplication cyst of the ileum.

The enteric duplication cyst is a term applied to an anomaly of the gut which presents as a cystic structure with a mucosal lining predominantly similar to that of the adjacent alimentary tract. It may be either due to an embryologic error in normal canalization or errors in the embryologic connection between the developing gut and neural tube, as a part of the split notochord syndrome. The preoperative diagnosis of a duplication cyst is difficult to make on the basis of conventional radiologic study including barium swallowing gastrointestinal series. With the wide application of ultrasound in the detection and evaluation of pediatric abdominal masses, an intra-abdominal cystic lesion may be encountered and the differential diagnoses may be difficult or impossible. We hereby report a case of duplication cyst of the ileum in which we believe its sonographic appearance is of certain value or even diagnostic in this pathology.

Child↗

PubMed1990

[Simple testicular cyst].

High-resolution sonograms of scrotum in two hundred and ninety six patients were reviewed. Twenty six patients were found to have simple testicular cyst(s). The specific features of cyst, which included sharp clear margin, anechoic content, posterior wall enhancement and no adjacent echogenic mass, could be found in all lesions. Four cases had bilateral testicular involvement. Solitary cystic lesion was found in 14 tests. The size ranged from 2.0 mm to 1.2 cm. Clustered cystic lesions were found in six testes. The size ranged from 4.0 mm to 2.5 cm. More than one focal lesion were found in 10 testes. Twenty four of these thirty testes had tunica albuginea cyst(s) or cyst(s) abutting on testicular margins. Four patients had follow-up sonograms with the period ranging from three months to two years. No remarkable change of all lesions were noted. The sonographic pictures and its patterns were presented. The pathogenesis and the literature were briefly reviewed.

Adolescent↗

PubMed1987

Identification of an intermediate of delta-aminolevulinate biosynthesis in Chlamydomonas by high-performance liquid chromatography.

The first committed intermediate of the chlorophyll biosynthetic pathway is delta-aminolevulinic acid (ALA). In plant cells, ALA is formed from glutamate by a pathway not yet clearly defined. One of the proposed pathways involves the reduction of glutamate to glutamate-1-semialdehyde (GSA) via a glutamyl-tRNA intermediate. GSA is then converted to ALA by an aminotransferase. We are studying this pathway using partially purified components from Chlamydomonas reinhardtii in in vitro reactions with [3H]L-glutamate as the substrate and analysis of the radioactive reaction products via HPLC. In reactions either lacking GSA-aminotransferase or containing gabaculine (an inhibitor of aminotransferase), a radioactive intermediate is formed which cochromatographs with synthetic GSA. As observed previously for ALA synthesis, the synthesis of this intermediate has an absolute requirement for RNA, ATP, and active enzymes, while the requirement for NADPH is less stringent. Both the accumulated intermediate and the synthetic GSA can be converted to ALA by the aminotransferase without any additional substrates or cofactors. These results support previous observations that GSA or a very similar compound is an intermediate of ALA synthesis.

Aminolevulinic Acid↗