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Biomedical subjects

L Ji

Publications and source records attributed to L Ji.

97 records · Page 6Linked to original sources
PubMed1992

Radioimmunoassays for melatonin using an antiserum raised against a novel antigen.

The highly specific antiserum to melatonin (MT) was produced, and the sensitivity and specificity of the radioimmunoassays (RIAs) using this antiserum was investigated. An immunogen was synthesized by binding 6-hydroxy-melatonin (6-OH-MT) to bovine serum albumin with a spacer of 6-bromohexanoic acid ethyl ester. Rabbits were immunized subcutaneously once a month with 1.0 mg of the immunogen for 7 months. The antiserum was characterized by a crossreactivity test by RIA using 125I-labelled MT. The antiserum specifically recognized MT but hardly did other analogues except for 6-OH-MT with a crossreactivity of only 0.4%. Two RIAs were established using [o-methyl-3H]MT and 2-[125I]iodo MT. In both RIAs, inhibition curves for MT were obtained in the range of 10 pg to 10 ng and 1-2 ng of MT inhibited the value of the assay at "0" by half. The similarity of the RIAs in sensitivity and inhibition by unlabelled MT is discussed on the basis of the structures of radioactive MTs and that of the immunogen.

Animals↗
PubMed1991

Radiation dosimetry by automatic image analysis of dicentric chromosomes.

A system for scoring dicentric chromosomes by image analysis comprised fully automatic location of mitotic cells, automatic retrieval, focus and digitization at high resolution, automatic rejection of nuclei and debris and detection and segmentation of chromosome clusters, automatic centromere location, and subsequent rapid interactive visual review of potential dicentric chromosomes to confirm positives and reject false positives. A calibration set of about 15,000 cells was used to establish the quadratic dose response for 60Co gamma-irradiation. The dose-response function parameters were established by a maximum likelihood technique, and confidence limits in the dose response and in the corresponding inverse curve, of estimated dose for observed dicentric frequency, were established by Monte Carlo techniques. The system was validated in a blind trial by analysing a test set comprising a total of about 8000 cells irradiated to 1 of 10 dose levels, and estimating the doses from the observed dicentric frequency. There was a close correspondence between the estimated and true doses. The overall sensitivity of the system in terms of the proportion of the total population of dicentrics present in the cells analysed that were detected by the system was measured to be about 40%. This implies that about 2.5 times more cells must be analysed by machine than by visual analysis. Taking this factor into account, the measured review time and false positive rates imply that analysis by the system of sufficient cells to provide the equivalent of a visual analysis of 500 cells would require about 1 h for operator review.

Cells, Cultured↗
PubMed1991

Purification and characterization of soybean root nodule ferric leghemoglobin reductase.

A ferric leghemoglobin reductase from the cytosol of soybean (Glycine max) root nodules was purified to homogeneity and partially characterized. The enzyme is a flavoprotein with flavin adenine dinucleotide as the prosthetic group and consists of two identical subunits, each having a molecular mass of 54 kilodaltons. The pure enzyme shows a high activity for ferric leghemoglobin reduction with NADH as the reductant in the absence of any exogenous mediators. The enzyme also exhibits NADH-dependent 2,6-dichloroindophenol reductase activity. A sequence of the first 50 N-terminal amino acids of the purified protein was obtained. Comparisons with known protein sequences have shown that the sequence of the ferric leghemoglobin reductase is highly related to those of the flavin-nucleotide disulfide oxido-reductases, especially dihydrolipoamide dehydrogenase of the pyruvate dehydrogenase complex.

Journal Article↗
PubMed1989

Characterization of insulin-like growth factor-I receptors in PC12 pheochromocytoma cells and bovine adrenal medulla.

Competitive binding studies indicated that PC12 cells have receptors for insulin-like growth factor-I (IGF-I). There are approximately 11,000 +/- 1,500 IGF-I receptors/cell; these receptors have an apparent KD for IGF-I of 7.2 +/- 0.6 nM. Covalent cross-linking of 125I-IGF-I to PC12 cells labeled a 125,000-130,000-Mr protein, presumably the alpha-subunit of the IGF-I receptor. Although PC12 cells also have insulin receptors, the 125I-IGF-I appeared to be cross-linked to IGF-I receptors, because 100 nM IGF-I competed for labeling but 100 nM insulin did not. Bovine chromaffin cells also have IGF-I receptors. The protein tyrosyl kinase activity of IGF-I receptors from bovine adrenal medulla and PC12 cells was examined after purification of the receptors by wheat germ agglutinin-Sepharose chromatography. IGF-I (10 nM) stimulated autophosphorylation of the beta-subunits of the IGF-I receptors from both preparations; the beta-subunits from both sources had Mr values of approximately 97,000. IGF-I also stimulated phosphorylation of the synthetic substrate poly(Glu:Tyr)4:1 by both receptor preparations. IGF-I (IC50 of approximately 0.2 nM) was much more potent than insulin at stimulating phosphorylation of poly(Glu:Tyr) by the bovine adrenal medulla preparation. A maximal concentration of IGF-I (10 nM) increased phosphorylation approximately threefold. IGF-I was slightly more effective than insulin at stimulating the phosphorylation of poly(Glu:Tyr) by the PC12 cell receptor preparation, but neither ligand produced a maximal effect at concentrations up to 100 nM. This result probably reflects the presence of comparable numbers of IGF-I and insulin receptors on PC12 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Gland Neoplasms↗