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Biomedical subjects

C J Chang

Publications and source records attributed to C J Chang.

At least 235 records · Page 13Linked to original sources
PubMed1987

Effect of nutrients and metabolic inhibitors on the growth of spiroplasmas.

Glycolytic intermediates replaced glucose as carbohydrate sources in a chemically defined medium CC-494N, whereas keto acids of citric acid cycle intermediates and glyoxylate were supplemented with 10 mM glucose. Glucose-6-phosphate, fructose-1,6-bisphosphate, 3-phosphoglyceraldehyde, and pyruvate supported limited growth for Spiroplasma floricola (23-6), whereas only pyruvate supported SR 3 spiroplasma and S. melliferum (AS 576). alpha-Ketoglutarate at 5 mM or greater, hematin, 2,4-dinitrophenol, sodium fluoride, and arsenite were dramatically inhibitory, whereas acetic anhydride, tricarballylate, acetylene dicarboxylate, and sodium cyanide were mildly inhibitory at 10 mM or lower. Malonate at 50 mM was not inhibitory.

Carbohydrate Metabolism↗
PubMed1986

Modification of calf thymus DNA by methyl methanesulfonate. Quantitative determination of 7-methyldeoxyguanosine by mass spectrometry.

Quantitation of 7-methyldeoxyguanosine (m7dG) produced in the in vitro methyl methanesulfonate (MeMS) action on calf-thymus DNA is achieved by enzymatic degradation, liquid chromatographic separation and chemical ionization mass spectrometry. The total degree of methylation, measured by uptake of [14C]MeMS was 0.35%. Mass spectral analysis shows that m7dG constitutes 84% of the total methylated product. It is also shown that tandem mass spectrometry allows detection of m7dG, as the protonated base, down to 1 pmol level, suggesting that MS/MS analysis can be the method of choice in quantitation of the adducts of in vivo DNA modifications.

Animals↗
PubMed1985

Chemical modification of nucleic acids. Methylation of calf thymus DNA investigated by mass spectrometry and liquid chromatography.

Mass spectrometry provides an extremely sensitive method for the identification and quantification of modified nucleosides and hence for determining chemical modifications of nucleic acids. When mass spectrometry is used in conjunction with a new high-performance liquid chromatographic system capable of separating 15 methylated and naturally occurring nucleosides, this allows the quantification of products of in vitro DNA methylation. With synthetic (2H3)methyl-labeled methylnucleosides as internal references, the distribution of methylated products formed when calf thymus DNA was reacted with N-methyl-N-nitrosourea(MeNU) was determined. Five modified products, 1-methyldeoxyadenosine(m1dA), 3-methyldeoxycytidine(m3dC), 7-methyldeoxyguanosine(m7dG), 3-methylthymidine(m3T) and O4-methylthymidine(m4T) were detected and the relative distributions were measured. The ability of mass spectrometry/mass spectrometry (tandem mass spectrometry) to increase specificity and sensitivity in this determination is demonstrated and its application to in vivo studies is suggested.

Animals↗
PubMed1984

Vitamin requirements of three spiroplasmas.

A chemically defined medium (CC-494M) was used to study the vitamin requirements of three spiroplasmas representing three distinct serogroups: flower spiroplasmas [Spiroplasma floricola and FS (SR-3)] and honeybee spiroplasma [HBS (AS-576)]. Nicotinic acid and riboflavin were essential to spiroplasma growth. Nicotinamide could substitute for nicotinic acid. Populations of S. floricola, FS (SR-3), and HBS (AS-576) reached 3.2 X 10(9), 1.96 X 10(10), and 6.1 X 10(9) CFU/ml, respectively, when nicotinic acid (0.036 mg/liter) and riboflavin (0.014 mg/liter) were supplied.

Ascorbic Acid↗
PubMed1984

Biosynthesis of ketomycin.

The antibiotic ketomycin is formed from shikimic acid via chorismic acid and prephenic acid. Phenylalanine and 2',5'-dihydrophenylalanine are not intermediates in the biosynthesis. Degradation of ketomycin derived from [1,6-14C]shikimic acid showed that prephenic acid is converted into ketomycin with stereospecific discrimination between the two enantiotopic edges of the ring, the pro-S-R edge giving rise to the C-2', C-3' side of the cyclohexene ring of ketomycin.

Anti-Bacterial Agents↗
PubMed1983

Reverse-phase high-performance liquid chromatography of chemically modified DNA.

A reverse-phase high-performance liquid chromatographic method has been developed to determine the sites of reaction and the product distribution of modified salmon sperm DNA. The DNA was reacted with methyl methanesulfonate in neutral solution, and then degraded into deoxyribonucleosides by snake venom phosphodiesterase and alkaline phosphatase. Four products were identified and quantitated: 7-methyldeoxyguanosine (37.1%), 7-methylguanine (7.3%), 3-methyldeoxycytidine (28.8%), and 1-methyldeoxyadenosine (26.8%). This method provides a rapid procedure for analysis of chemically or biochemically modified nucleic acids.

Animals↗
PubMed1983

Nutritional requirements of two flower spiroplasmas and honeybee spiroplasma.

A chemically defined medium (CC-494) was used to study the nutritional requirements of three spiroplasmas representing three distinct serogroups: flower spiroplasmas [Spiroplasma floricola and FS (SR-3)] and honeybee spiroplasma [HBS (AS-576)]. Glucose, fructose, and mannose were utilized by all three spiroplasmas. In addition, the honeybee spiroplasma could ferment trehalose, FS (SR-3) could ferment sucrose, and S. floricola could ferment trehalose, sucrose, and raffinose. The three spiroplasmas varied greatly in their requirements of amino acids for growth. S. floricola was the only strain that utilized arginine. HBS (AS-576) required at least one purine and one pyrimidine base (either free base or ribonucleoside) for growth, while both flower spiroplasmas grew with only one base in the medium. Oleic acid, cholesterol, and bovine serum albumin were essential to all three spiroplasmas. Palmitic acid, which was nonessential, promoted growth significantly.

Amino Acids↗
PubMed1982

Spiroplasmas: cultivation in chemically defined medium.

A chemically defined medium, CC-494, supports the cultivation in vitro of several spiroplasmas belonging to three distinct serogroups. Medium CC-494 supports the growth of flower spiroplasmas FS 23-6 and FS SR-3 and of honey bee spiroplasma HBS AS-576. The maximal populations of the two flower spiroplasmas and honey bee spiroplasma are comparable to those cultured in the undefined medium C-3G. The growth rate for all three spiroplasmas is slower in the defined medium.

Culture Media↗
PubMed1982

Purification and properties of NADP-linked, alcohol dehydrogenase from Entamoeba histolytica.

An NADP-linked, alcohol dehydrogenase from Entamoeba histolytica was purified to apparent homogeneity by Blue Sepharose affinity chromatography. Molecular weights of 130,000 and 30,000 were estimated by gel filtration and by sodium dodecyl sulfate polyacrylamide gel electrophoresis, respectively, suggesting that the enzyme is a tetramer. The enzyme exhibited more than 20-fold selectivity for NADP(H) over NAD(H). Although the purified enzyme acts on both primary and secondary alcohols, higher activity was found with secondary alcohols.

Alcohol Oxidoreductases↗
PubMed1981

Biosynthesis of the macrolide antibiotic chlorothricin.

Feeding experiments with 13C-labeled precursors followed by 13C NMR analysis of the antibiotic and its aglycon have established a polyketide mode of biosynthesis for chlorothricin, a metabolite of Streptomyces antibioticus. The acyl moiety is a substituted 6-methylsalicylic acid derived from four acetate units and a methyl group of methionine. The aglycon is comprised of ten acetate and two propionate units, leaving three carbon atoms, C-22, -23, and -24, unaccounted for. The two 2-deoxy-D-rhamnose moieties are derived from glucose with retention of the hydrogens at C-1, C-2, and C-6 and loss of H-3 and H-5. The hydrogen at C-4 of glucose is transferred intramolecularly to C-6 of the hexose, replacing the hydroxyl group at C-6 in an inversion mode, a result which implicates the thymidine 5'-diphosphate-glucose oxidoreductase reaction in this transformation.

Acetates↗
PubMed1981

The biosynthesis of the antibiotic pyrrolnitrin by Pseudomonas aureofaciens.

Feeding experiments with tryptophan samples labeled specifically with radioactive and stable isotopes have shown that Pseudomonas aureofaciens converts this amino acid into pyrrolnitrin in such a way that the indole nitrogen gives rise to the nitro group, the amino group becomes the pyrrole nitrogen, C-3 of the precursor side chain becomes C-3 of the antibiotic, and H-2 of the indole ring and H-alpha of the side chain give rise to H-5 and H-2 of pyrrolnitrin, respectively. Only the L-isomer of tryptophan is incorporated with retention of the alpha-hydrogen and the amino nitrogen. From the D-isomer the labels from these two positions are lost. The obvious conclusion that L-tryptophan is the more immediate precursor is, however, contradicted by the better incorporation of D- than L-tryptophan into the antibiotic. Several potential pathway intermediates were evaluated for incorporation and 4-(0-aminophenyl)-pyrrole was found to be a good precursor. The results area discussed in terms of a plausible pathway for pyrrolnitrin biosynthesis.

Antifungal Agents↗