PubMed Health⌕ Search

Biomedical subjects

C Chang

Publications and source records attributed to C Chang.

At least 397 records · Page 22Linked to original sources
PubMed1985

Mechanism of the pyrophosphate migration in the enzymatic cyclization of geranyl and linalyl pyrophosphates to (+)- and (-)-bornyl pyrophosphates.

Soluble enzymes from sage (Salvia officinalis) and tansy (Tanacetum vulgare), which catalyze the cyclization of geranyl pyrophosphate and the presumptive intermediate linalyl pyrophosphate to the (+) and (-) enantiomers, respectively, of 2-bornyl pyrophosphate, were employed to evaluate mechanistic alternatives for the pyrophosphate migration in monoterpene cyclization reactions. Separate incubation of [1-3H2,alpha-32P]- and [1-3H2,beta- 32P]geranyl and (+/-)-linalyl pyrophosphates with partially purified preparations of each enantiomer-generating cyclase gave [3H, 32P]bornyl pyrophosphates, which were selectively hydrolyzed to the corresponding bornyl phosphates. Measurement of 3H:32P ratios of these monophosphate esters established that two ends of the pyrophosphate moiety retained their identifies in the cyclization of both precursors to both products and also indicated that there was no appreciable exchange with exogenous inorganic pyrophosphate in the reaction. Subsequent incubations of each cyclase with [8,9-14C,1-18O]geranyl pyrophosphate and with (1E)-(+/-)-[1-3H,3-18O]linalyl pyrophosphate gave the appropriate (+)- or (-)-bornyl pyrophosphates, which were hydrolyzed in situ to the corresponding borneols. Analysis of the derived benzoates by mass spectrometry demonstrated each of the product borneols to possess an 18O enrichment essentially identical with that of the respective acyclic precursor. The absence of P alpha-P beta interchange and the complete lack of positional 18O isotope exchange of the pyrophosphate moiety are compatible with tight ion pairing of intermediates in the coupled isomerization-cyclization of geranyl pyrophosphate and establish a remarkably tight restriction on the motion of the transiently generated pyrophosphate anion with respect to its cationic terpenyl reaction partner.

Acyclic Monoterpenes↗
PubMed1985

Copper(I)-bleomycin: structurally unique complex that mediates oxidative DNA strand scission.

Copper(I)-bleomycin [Cu(I) X BLM] was characterized in detail by 13C and 1H NMR. Unequivocal chemical shift assignments for Cu(I) X BLM and Cu(I) X BLM X CO were made by two-dimensional 1H-13C correlated spectroscopy and by utilizing the observation that Cu(I) X BLM was in rapid equilibrium with Cu(I) and metal-free bleomycin, such that individual resonances in the spectra of BLM and Cu(I) X BLM could be correlated. The binding of Cu(I) by bleomycin involves the beta-aminoalaninamide and pyrimidinyl moieties, and possibly the imidazole, but not N alpha of beta-hydroxyhistidine. Although no DNA strand scission by Cu(II) X BLM could be demonstrated in the absence of dithiothreitol, in the presence of this reducing agent substantial degradation of [3H]DNA was observed, as was strand scission of cccDNA. DNA degradation by Cu(I) X BLM was shown not to depend on contaminating Fe(II) and not to result in the formation of thymine propenal; the probable reason(s) for the lack of observed DNA degradation in earlier studies employing Cu(II) X BLM and dithiothreitol was (were) also identified. DNA strand scission was also noted under anaerobic conditions when Cu(II) X BLM and iodosobenzene were employed. If it is assumed that the mechanism of DNA degradation in this case is the same as that under aerobic conditions (i.e., with Cu(I) X BLM + O2 in the presence of dithiothreitol), then Cu X BLM must be capable of functioning as a monooxygenase in its degradation of DNA.

Bleomycin↗
PubMed1985

Photosensitization of mitochondrial adenosine-triphosphatase and adenylate kinase by hematoporphyrin derivative in vitro.

Mitochondrial ATPase and adenylate kinase activity of hepatoma cells were inhibited by hematoporphyrin derivative (HPD) followed by photoirradiation. Inhibition of ATPase activity was a dose- and time-related event. Malonaldehyde (MDA) content of mitochondrial membranes was markedly increased by HPD plus light. The content of mouse liver microsomal cytochrome P-450 was greatly increased after intraperitoneal injection of HPD for 4 days (5 mg/kg/day). The liver weight, and levels of liver microsomal G-6-phosphatase, MDA and triglyceride (TG) showed no difference in treated vs. control animals. The data presented here demonstrate that mitochondria may be a sensitive site of action of HPD photosensitization, and inactivation of ATPase and adenylate kinase may be an important contributing factor to tumor cell damage and death.

Adenosine Triphosphatases↗
PubMed1985

Bacterial tracheitis, diagnosis and treatment.

During a 22-month period, 5 children, 6-13 months of age, presented with an acute obstructive upper airway infection which resembled both croup and epiglottitis. All 5 failed to respond to standard treatment for croup, including aerosolized racemic epinephrine. In all patients, direct laryngoscopy revealed minimal or no change in the epiglottis and aryepiglottic folds but severe subglottic swelling and copious purulent tracheal secretions. Gram stains of the purulent secretions revealed many polymorphonuclear leukocytes with gram-positive cocci (3 patients) and small gram-negative rods (2 patients). Cultures subsequently confirmed the presence of S. Aureus and H. Influenzae. Initial therapy for all patients included endotracheal intubation, antibiotic therapy for both S. Aureus and H. Influenzae and frequent tracheal suctioning. Hospitalization varied from one to 3 weeks. We reported findings in these patients because: the initial diagnosis was unclear due to confusion caused by clinical features common to both croup and epiglottitis and bacterial tracheitis requires a prompt accurate diagnosis and aggressive antibiotic and airway management in order to prevent unnecessary morbidity and mortality.

Airway Obstruction↗
PubMed1985

Magnesium deficiency and myocardial infarct size in the dog.

Although epidemiologic data suggest a relation between myocardial infarction death rates and dietary intake of magnesium, there are no experimental studies reflecting such a phenomenon. It is now reported that beagle dogs kept on a severely magnesium-deficient diet for 100 days develop a larger infarct than do control animals. Control animals were either kept on the same diet as experimental animals with supplementary magnesium, or were fed standard dog chow. The control groups were indistinguishable and were therefore pooled. Infarction was produced by occlusion of the left anterior descending coronary artery for 1 hour followed by 4 hours of reperfusion. Slices of ventricular myocardium, 5 mm thick, were made from the apex to the base. Ischemic muscle, considered to be the muscle at risk, was delineated by a microsphere-autoradiographic method, and necrotic muscle was delineated by tetrazolium stain. Involved areas were measured by planimetry, and these integrated to produce the volume. The volumes of muscle made ischemic were similar in the experimental and control groups. The volumes of necrotic muscle, however, were less in the control than in the experimental animals. The ratio of necrotic muscle volume to the volume of muscle at risk was greater in the experimental animals than in the control animals by a factor of almost two (p less than 0.004). These experiments indicate that, under the conditions used here, animals fed a magnesium-deficient diet develop a larger infarct than do control animals. This could occur either through decreased postocclusion collateral flow or increased vulnerability of the ischemic muscle in magnesium-deficient animals. Although these experiments cannot rule out an effect on postocclusion collateral flow, they do suggest that electrolyte abnormalities related to magnesium deficiency are of such a character as to increase myocardial vulnerability to injury.

Animals↗
PubMed1985

Mutations that impair a posttranscriptional step in expression of HLA-A and -B antigens.

Mutations can interfere with posttranscriptional expression of the HLA-A and -B genes. B-lymphoblastoid cells that contain one copy of the major histocompatibility complex (MHC) were subjected to mutagenesis and immunoselection for MHC antigen-loss mutants. Some mutations partially reduced surface expression of HLA-A and eliminated HLA-B expression concurrently, although the HLA-A and -B genes were present and transcribed. Antigen expression was fully restored in hybrids of these mutants with other B-lymphoblastoid cells. Therefore, normal cell surface expression of the HLA-A and -B antigens on B lymphoblasts requires (i) execution of at least one trans-active step in the production of the antigens after transcription of the HLA-A and -B genes or (ii) association of the class I antigens with other molecules. DNA analysis of one mutant suggests the possibility that a locus required for the normal expression of the HLA-A and -B antigens is located between the MHC complement genes and the HLA-DP alpha II locus.

Antibodies, Monoclonal↗
PubMed1985

Interrelationship of dietary Mg intake and electrolyte homeostasis in hamsters: I. Severe Mg deficiency, electrolyte homeostasis, and myocardial necrosis.

Epidemiological studies indicate a strong relationship between dietary Mg intake and the incidence of sudden cardiac death. The mechanism by which dietary Mg leads to an increased incidence of cardiovascular disease is unknown but may involve alteration of electrolyte balance. In the present study, tissue electrolyte levels and myocardial pathology were investigated in adult hamsters fed a diet containing no added Mg. Control animals were fed the same diet supplemented with Mg or standard laboratory chow. Hamsters were killed after 4, 8, 12, or 18 days on the test diet, and levels of Na, K, Ca, and Mg were measured in the serum, myocardium, bone, and kidney. The earliest change induced by the test diet was a decrease of the serum Mg and an increase in the Na concentration of the myocardium and other tissues. Following the rise in myocardial Na, the myocardial Ca rose, attaining a fourfold increase by 18 days. K fell in heart and kidney, but not significantly. Although there was no significant change in myocardial Mg, foci of myocardial necrosis, considered to be typical of acute severe Mg deficiency, were found. Myocardial necrosis and the increase in myocardial Ca occurred in parallel. Because of the pattern of observed changes in electrolyte levels, and the potential role of Ca in myocardial injury, the occurrence of myocardial necrosis in these Mg-deficient hamsters is attributable to the increased level of myocardial Ca, rather than to any change in intracellular Mg levels. It is postulated that reduced extracellular Mg levels increase [Na]i through reduction of sarcolemmal (Na+ + K+)-ATPase activity. This would lead to an increase in [Ca]i through Na-Ca exchange.

Acid-Base Equilibrium↗
PubMed1984

The detection of HLA-DR, MB and MT determinants on purified class II molecules by inhibition of microcytotoxicity.

An assay has been developed which makes it possible to determine the HLA allospecificities carried by molecules in purified fractions of detergent lysates from EBV-transformed human lymphocytes. It is based on inhibition of the standard microlymphocytotoxic test used for identifying HLA class I and II antigens with alloantisera. Soluble cell membrane products from EBV-transformed cell lines homozygous for the HLA region gave specific inhibition of standard typing antisera. The test requires preincubation of microliter volumes of soluble antigen preparations maintained in 0.05% NP-40 with selected antisera prior to adding EBV-transformed cells as target cells. It was possible using this assay to follow isolation of the structurally related human class II molecules bearing the MB and DR specificities. Detergent lysates of cells were fractionated on affinity columns prepared from monoclonal antibodies directed against distinct class II antigens. Eluates from these columns contained the expected DR and MB specificities. The assay is easy to perform, highly reproducible and allows multiple determinations.

Antibodies, Monoclonal↗
PubMed1984

The use of a hydroxylapatite-filter steroid receptor assay method in the study of the modulation of androgen receptor interaction.

Receptors for androgen, estrogen, and glucocorticoid can be assayed by hydroxylapatite adsorption of the radioactive steroid-receptor complex and washing of the adducts on membrane filters mounted on a multiple filter holder. The method is economical, very rapid and sensitive. This new receptor assay method was used to study the modulation of androgen receptor of rat ventral prostate by metal ions, thiols, and ligand structure. The interaction of androgen with the naked receptor is inhibited by 10 microM ZnCl2, CdSO4, or CuSO4 but this inhibition is competed by androgen and is reversed by DTT. The androgen-receptor complex is less sensitive to divalent metal ions but Zn2+, at 3 mM, appears to alter the conformation of the receptor and promote the release of androgen. Certain phenanthrene derivatives exhibited striking structural specificities in their ability to compete with radioactive androgen for binding to the prostate receptor. The results suggest that the receptor has binding preference toward individual ring structure in the steroid.

Animals↗
PubMed1984

Cloning and mapping of Saccharomyces cerevisiae photoreactivation gene PHR1.

The yeast Saccharomyces cerevisiae, like most organisms, is able to directly repair pyrimidine dimers by using a photoreactivating enzyme and visible light. Cells carrying the phr1 mutation were shown previously to be unable to photoreactivate dimers, but neither the map position nor the primary gene product of the PHR1 gene has been determined. We have cloned this gene and determined its map position. A plasmid containing a 6.4-kilobase yeast DNA insert has been isolated and shown to restore photoreactivation in a phr1 strain. A 3.1-kilobase subclone has also been shown to complement phr1. The original plasmid was targeted to integrate into chromosomal DNA at a site homologous to the insert by cutting within the insert. Two of these integrants have been mapped on the right arm of chromosome XV; the integrants have been further mapped at ca. 13 centimorgans from prt1. It has also been independently determined that phr1 maps at this location. Thus, we have determined the map position of PHR1 and also have shown that the plasmid contains PHR1 rather than a suppressor of the phr1 mutation.

Chromosome Mapping↗
PubMed1983

A simple ashing method for determination of Mg and Ca in laboratory animal feed and tissues.

A simple procedure has been developed for preparation of animal tissues and diet mixtures for Mg and Ca analysis by atomic absorption spectroscopy. This procedure involves wet ashing in warm 30% hydrogen peroxide and extraction of metals, from the dried ash, into cold, dilute nitric acid. Less than 200 mg of tissue or feed are required. Measurements obtained by this method for hamster and rat myocardium give values similar to those found previously by more cumbersome methods. Concentrations of Mg and Ca in hamster serum, bone, kidney, and liver are also reported. Recovery of magnesium from bone and heart tissue was 101% and 102%, respectively. For calcium the respective values were 99% and 98%. This procedure is simple to carry out, does not generate corrosive fumes or require expensive equipment. It can be conveniently used to prepare large numbers of samples for atomic absorption spectrophotometry.

Animal Feed↗
PubMed1983

Induction of plasma protein secretion in a newly established human hepatoma cell line.

To study the expression and the regulation of hepatocyte markers, we have undertaken to establish human hepatoma cell lines of various phenotypes. We now report the establishment of a new human hepatoma cell line, HA22T/VGH. This cell line has many of the properties of human hepatocellular carcinoma. Only 5 of 15 plasma proteins investigated were detected in the medium of a 10-day-old HA22T/VGH culture. However, when the HA22T/VGH cells and a clonal derivative, C5, were cultured in an aggregated form, all 15 plasma proteins were found in the culture medium. These results indicate that hepatoma cell lines with different phenotypes can be established, and they provide a good experimental framework to investigate differentiation of human hepatocytes.

Animals↗
PubMed1982

Deglyco-bleomycin. Degradation of DNA and formation of a structurally unique Fe(II) . CO complex.

In analogy with bleomycin, deglyco-bleomycin B2 has been found to form a stable, diamagnetic complex with Fe(II) and CO. Although the stoichiometry of this complex appeared to be the same as that formed with bleomycin, the geometry of the deglyco-bleomycin complex was fundamentally different, especially as regards orientation of the beta-aminoalanine moiety. In the presence of Fe(II) and O2, deglyco-bleomycin A2 and deglyco-bleomycin B2 were found to release [3H]thymine from radiolabeled PM-2 DNA; when employed at limiting concentrations, deglyco-bleomycin A2 and B2 gave about half as much [3H]thymine release as the respective bleomycins. In view of the spectral evidence (Burger, R. M., Horwitz, S. B., Peisach, J., and Wittenberg, J. B. (1979) J. Biol. Chem. 254, 12299-12302) that Fe(II) . bleomycin . CO has the same geometry as the complex formed by initial association of bleomycin, Fe(II), and O2, the accumulated data suggest strongly that all metal complexes of bleomycin (derivatives) capable of DNA degradation need not have the same geometry.

Bleomycin↗
PubMed1982

Generation of cytotoxic lymphocytes by SV40-induced antigens.

In order to study the correlation of in vivo tumor transplantation immunity and in vitro immunologic assays, cell-mediated cytotoxicity against SV40-transformed cells was studied in AL/N strain mice by using 51Cr-release assay. Killing of SV40-transformed AL/N fibroblast cells was observed by spleen cells of AL/N mice immunized with syngeneic SV40-transformed cells. Immunization with the solubilized SV40 tumor-specific transplantation antigen (TSTA) that induced transplantation immunity in vivo did not elicit cytotoxic spleen cells in vitro. However, the spleen cells from mice immunized with solubilized TSTA and then sensitized in vitro with SV40-transformed cells became cytotoxic against SV40-transformed fibroblasts. Similarly, SV40 TSTA (T antigen) purified by immunoprecipitation was able to prime the lymphocytes in AL/N mice: the primed lymphocytes could differentiate into cytotoxic lymphocytes upon in vitro stimulation by SV40-transformed cells. These data indicate that SV40 TSTA (T antigen) plays a role in the induction of cytotoxic lymphocytes.

Animals↗
PubMed1982

Inhibition of intercellular communication in Chinese hamster V79 cells by teleocidin.

Teleocidin, a mixture of teleocidin A and teleocidin B, was found to block metabolic cooperation between the 6-thioguanine-resistant and the 6-thioguanine-sensitive cells in the Chinese hamster V79 cell system. A teleocidin B preparation containing two isomers exerted the same effect. The dose-response curves of these two compounds were, in general, similar to that of 12-O-tetradecanoyl-phorbol-13-acetate, a powerful mouse skin tumor promoter. Upon hydrolysis with 6M hydrochloric acid containing 4% thioglycolic acid, teleocidin lost most of its ability to block metabolic cooperation. This was probably caused by the conformational change resulting from the rupture of the nine-membered lactam ring of teleocidin.

Alkaloids↗
PubMed1981

Chemical modification of ribonucleic acid. A direct study by carbon-13 nuclear magnetic resonance spectroscopy.

Direct study of the methylation of ribonucleic acid with methyl methanesulfonate by carbon-13 nuclear magnetic resonance spectroscopy has demonstrated the usefulness of this method in studying the chemical modification of biomacro-molecules and the interaction between nucleic acids and biologically active agents. This direct stable isotope method eliminated all tedious and questionable degradation processes for determining the reactive sites and the product distributions. Six methylated products, 7-methylguanosine, 1-methyladenosine, 3-methylcytidine, 1-methylguanosine, 3-methyluridine, and methyl phosphodiester, were identified by comparison with many model compounds and careful examination of spin-spin coupling and spin-lattice relaxation time. An extensive study of the interaction of phosphate buffer with methyl methansulfonate accounted for the sharp difference in the 13C spectra of the methylated RNA isolated from the reactions controlled by a pH-stat and phosphate buffer, respectively. The 13C-enriched agent significantly enhances the specificity and sensitivity of the method and provides better quantitative results.

Carbon Isotopes↗