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Biomedical subjects

G W Chang

Publications and source records attributed to G W Chang.

34 records · Page 2Linked to original sources
PubMed1981

An enzymatic assay for available zinc in plasma and serum.

A convenient enzymatic assay for available zinc in plasma and serum was developed. The assay is based upon the reactivation of the zinc metalloenzyme alkaline phosphatase which had been previously inactivated by nitrilotriacetic acid. The enzymatic assay was applied to serum samples from human subjects in a study of zinc utilization in pregnancy and to plasma samples from rats in a zinc deficiency study. Most plasma samples with low zinc levels (less than 70 microgram/dl) reactivated the enzyme to less than 30% of control activity. Most samples with normal zinc levels (70-120 microgram/dl) reactivated the enzyme 30-65%. Samples with elevated zinc levels (greater than 120 microgram/dl) reactivated the enzyme over 70%. The assay is quick, convenient, and in principle measures functionally available zinc.

Alkaline Phosphatase↗
PubMed1979

Formate dehydrogenase mutants of Salmonella typhimurium: a new medium for their isolation and new mutant classes.

We have designed a new medium for the differentiation of mutants of Salmonella typhimurium defective in the ability to reduce nitrate with formate, and have characterized 24 formate dehydrogenase (FDH) mutants isolated on this medium. The mutants were assayed for the ability to use formate to reduce benzyl viologen and phenazine methosulfate, and were mapped by means of conjugation and P22-mediated transduction. Mutants lacking the ability to reduce either dye were found to map at three distinct sites: at a site co-transducible with xyl (presumably fdhA), at a site or sites between 13U and 33U, but not co-transducible with aroA, bio, purB, pyrC, or pyrD (near, but not identical with fdhB), and at asite 10-20% co-transducible with pyrE, for which we suggest the designation fdhC. Six mutant isolates reduced benzyl viologen, but not phenazine methosulfate. They retained the ability to produce nitrite during growth with nitrate. They mapped between 83U and 89U, but no co-transduction was found with metE, glnA, metB, or argH. The combined biochemical and genetic data suggest the existence of a gene in this area which is essential for the reduction of nitrate with formate, but not for formate hydrogenlyase activity or for nitrate reductase activity.

Aldehyde Oxidoreductases↗
PubMed1979

Cysteine auxotrophs of Salmonella typhimurium which grow without cysteine in a hydrogen/carbon dioxide atmosphere.

Cysteine auxotrophs of Salmonella typhimurium mutated in cysB, cysI or cysJ grew with sulphate as a sulphur source when incubated under a hydrogen/carbon dioxide atmosphere. Yields obtained under these conditions were equivalent to those characteristic of wild-type S. typhimurium. The same mutants failed to grow with sulphate as a sulphur source when incubated aerobically. Auxotrophs mutated in cysA, cysC, cysD, cysE, cysG and cysH required cysteine for growth under both incubation conditions. The results suggest that mutations in cysB (regulation of the several cys operons) and also cysI and cysJ (sulphite reductase activity) can be circumvented during anaerobic growth under hydrogen.

Anaerobiosis↗
PubMed1978

Detection of mutagens produced by fungi with the Salmonella typhimurium assay.

Forty-one fungal isolates (one isolate per species) representing common plant pathogens and food crop contaminants were grown on sterile, polished rice and assayed for mutagenic activity in the Salmonella typhimurium-microsome system. Initially, single doses of aqueous and chloroform extracts of the moldy rice were assayed against the TA100 tester strain by incorporating extracts into the growth medium and by applying small quantities on disks placed on the agar surface. Suspected activity was examined further by analysis of several doses in the plate incorporation assay. Extracts of two aflatoxin-producing isolates (Aspergillus flavus and A. parasiticus) showed pronounced mutagenic activity, as did extracts of five other isolates (A. heterothallicus, A. nidulans, A. terricola, Alternaria tenuis, and Fusarium moniliforme) which did not contain detectable aflatoxins. Seven additional isolates (Botrytis cineria, Ceratocystis fimbriata, Cladosporium herbarum, Fusarium solani f. sp. pisi, Penicillium oxalicum, Thermomyces lanuginosus, and Verticilium albo-atrum) revealed activity which was possibly mutagenic; i.e., mutagenic responses were not observed in both the disk and incorporation assays, and clear dose-related activity was not observed in the incorporation assay. Extracts of the remaining fungi were not mutagenic in the bacterial assay.

Food Microbiology↗
PubMed1977

Mutagenic activity of quercetin and related compounds.

The mutagenic activities of several flavonoids and flavonoid metabolites were examined by means of Salmonella typhimurium mutants that reveal base-pair substitution and frameshift mutagens. Of the compounds tested (naringin, rutin, neohesperetin, hesperetin, dihydroquercetin, quercetin, quercetin pentaacetate, permethylquercetin, m-hydroxyphenylacetic acid, and m,p-dihydroxyphenylacetic acid), only quercetin was mutagenic without microsomal activation. With activation, however, the mutagenic activity of quercetin was increased significantly and that of quercetin pentaacetate was revealed. The health implications of these findings and aspects of flavonoid structural requirements for mutagenic activity are discussed.

Dose-Response Relationship, Drug↗
PubMed1976

Rapid thin layer chromatographic method for the detection of histamine in fish products.

A rapid, convenient thin layer chromatographic (TLC) method for detecting histamine in fish samples is described. Samples of press juice or fish flesh are applied directly to TLC plates. The plates are developed with acetoneammonium hydroxide (95+5) and the spots are visualized with ninhydrin or Pauly's reagent. Chromatographic separation of histamine from other fish components is readily achieved by this method.

Chromatography, Thin Layer↗
PubMed1971

Enriched selection of dominant mutations: histidine operator mutations.

In the course of selection of bacteria with derepressed levels of histidine biosynthetic enzymes, it was found that when mutagen-treated cells were spread on a selective medium without allowing intervening growth to occur, the frequency of operator mutants obtained was dramatically increased. This may be useful as a general enrichment for operator or other dominant mutations.

Alanine↗
PubMed1971

Histidine regulation in Salmonella typhimurium. 8. Mutations of the hisT gene.

The hisT gene, one of six genes in which mutation causes derepression of the histidine operon in Salmonella typhimurium, is shown to code for a protein that is not essential for the growth of the bacteria. This is indicated by the characterization of particular classes of mutations in the hisT gene: amber mutations, frame-shift mutations, and temperature-sensitive mutations that affect repression but not growth. In addition, the class of semilethal mutations was selected for but not found.

Alanine↗