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L T Chang

Publications and source records attributed to L T Chang.

At least 19 recordsLinked to original sources
PubMed1991

Decreased production of para-hydroxypenicillin V in penicillin V fermentations.

Penicillin V (phenoxymethyl penicillin) is produced by industrial strains of Penicillium chrysogenum in the presence of phenoxyacetic acid (POAc), a side-chain precursor for the penicillin V molecule. The wild-type strain of P. chrysogenum produces an undesirable penicillin byproduct, para-hydroxypenicillin V (p-OH penicillin V), in addition to penicillin V, via para-hydroxylation of POAc and subsequent incorporation of the p-OH phenoxyacetic acid into the penicillin molecule. Most of the p-OH penicillin V is produced late in cycle when the POAc concentration in the medium is nearly depleted. The level of p-OH penicillin V produced by the control strain ranges up to 10-15% of the total penicillins produced. 3-Phenoxypropionic acid and p-bromophenylacetic acid partially inhibit the formation of p-OH penicillin V with a minimal effect on penicillin V productivity. Mutants deficient in their ability to hydroxylate POAc were found to produce lower levels of p-OH penicillin V. Multi-step mutation and screening, starting with the wild-type strain, have culminated in isolation of mutants which produce p-OH penicillin V as 1% of the total penicillins with no adverse effect on penicillin V productivity.

Fermentation↗
PubMed1990

Penicillin production by glucose-derepressed mutants of Penicillium chrysogenum.

Wild-type strains of Penicillium chrysogenum produce lower penicillin V titers in media containing excess glucose. Two mutant strains were isolated and shown to produce normal penicillin V titers in the presence of excess glucose. These strains, designated as glucose-repression insensitive (GRI) mutants, produced higher penicillin V titers than the wild-type strain in media containing lactose as the main carbohydrate source. In lactose-based media, the production of penicillin V was depressed to a much lesser extent by in-cycle additions of glucose with the GRI mutants when compared to the wild-type strain. In short-term biosynthesis experiments using washed cells in a medium containing glucose as the sole carbon source, the GRI mutants produced penicillin V at a faster rate than the wild-type strain. In fed-batch fermentations in 14-liter fermentors, where glucose was fed continuously and pH controlled, both GRI mutants produced more than 10% higher penicillin V titers than the wild-type strain. These results suggest that isolation of GRI mutants is an effective way to select for higher producing strains and that the synthesis of penicillin synthesizing enzymes in GRI mutants may be less repressed by glucose than in wild-type strains.

Culture Media↗
PubMed1989

Estradiol secretion by the ovarian tissue, in response to hypophyseal stimulation, during ontogenesis of the bullfrog.

Ovaries of tadpoles, froglets, young frogs, and mature frogs of Rana catesbeiana were cut into small pieces. They were incubated for 6 hr in Krebs-Ringer bicarbonate buffer as controls. Another series of ovaries of the same developmental stages were incubated with pituitary extracts in the buffer as experimentals. Media were then analyzed for estradiol secretion by radioimmunoassay. The results showed that estradiol secretion by tadpole ovaries during development was not affected by the addition of pituitary extracts of mature frogs in the media at any stage while those of young and mature frogs with pituitary extracts secreted more estradiol than those without. These findings indicate that tadpole ovaries are unresponsive to pituitary agents to produce estradiol while frog ovaries are dependent on some pituitary hormones to synthesize estradiol. Thus frog ovaries acquire dependence on the pituitary agent only after metamorphosis.

Animals↗
PubMed1988

In vitro inhibition of estradiol secretion of tadpole ovaries by cyanoketone.

We have demonstrated the presence of delta 5-3 beta-hydroxysteroid dehydrogenase (HSD) activity in tadpole ovaries of Rana catesbeiana. In the present study, we wish to determine whether estradiol (E2) secretion of tadpole ovaries could be influenced by cyanoketone (CK), a specific inhibitor of delta 5-3 beta-HSD. R catesbeina tadpoles at the premetamorphic climax were used, and pooled ovaries were incubated, 30 mg/tube, with CK at dosages of 0, 0.001, 0.01, 0.1, 1, and 10 micrograms/ml of Krebs-Ringer bicarbonate buffer for 6 hr. Media were collected for assay of E2 by radioimmunoassay (RIA). Results showed an inhibition of E2 secretion by CK that was positively correlated with CK dosage, but plateaued at doses of 0.1 microgram/ml and higher. This finding was comparable to that of G.F. Young, H. Kagawa, and Y. Nagahama (1982, Gen. Comp. Endocrinol. 47, 357-360) on adult fish ovaries. However, adult vertebrates depend on gonadotropins to regulate secretion of E2 while tadpoles, being immature, might secrete E2 independently of pituitaries. When the histochemical test for delta 5-3 beta-HSD activity was performed on in vitro CK-treated ovaries, there was a decrease of enzyme activity by CK. The RIA and histochemical findings may contribute to the concept of sex transformation in which a disturbance of steroidogenesis may induce sex reversal from females to males, at least in tadpoles.

Androstenols↗
PubMed1988

Estrogen suppression of preincubated tadpole ovaries in vitro by cyanoketone.

In a previous RIA study we found that cyanoketone (CK) inhibited ovarian E2 secretion of tadpoles in vitro and that this inhibition effect was through inactivation of delta 5-3 beta-HSD activity. A complete 100% inhibition was expected at a CK dosage of 0.1 microgram/ml of the medium, but, instead, it was 85%. The discrepancy might be due to the fact that the previous experiments did not preincubate the ovaries with CK in order to get rid of the residual E2. To this end, the present study was designed. Tadpole ovaries of Rana catesbeiana were preincubated with CK of a dosage of 0, 0.001, 0.01, 0.1, 1, or 10 micrograms/ml of the KRbb medium for 30 min. The media were discarded. Fresh media with the same series of CK doses were added to the ovaries and were incubated again for 6 hr. The media were collected for RIA of estrogen. The results showed the same tendency of estrogen inhibition as the previous study. However, a maximal inhibition effect of 95% was obtained at the dose of 0.1 microgram/ml. Therefore, the difference between non-preincubation of the previous experiments and preincubation of the present study does exist as we predicted.

Androstenols↗
PubMed1987

Contrasting effects of ACTH and cyanoketone on delta 5-3 beta-hydroxysteroid dehydrogenase activity in interrenal glands of tadpoles of Rana catesbeiana in vitro.

The present communication describes an investigation of stimulation and inhibition of delta 5-3 beta-hydroxysteroid dehydrogenase in interrenal glands of tadpoles of Rana catesbeiana. Frozen sections of interrenal glands, together with kidneys, were prepared histochemically for assay of delta 5-3 beta-HSD activity. Concentrations of 0.01, 0.1, 1, and 10 IU/ml of ACTH or of 0.01, 0.1, 1, and 10 micrograms/ml of cyanoketone were added to the incubation media. The reaction products of the histochemically prepared slides, in terms of absorbance, were scanned at a defined area with a computerized microscope spectrophotometer. The results indicate that ACTH causes a significant dose-response stimulation of delta 5-3 beta-HSD activity in tadpole interrenals; cyanoketone, on the other hand, causes significant dose-dependent inhibition.

3-Hydroxysteroid Dehydrogenases↗
PubMed1985

In vitro estradiol synthesis and secretion by tadpole ovaries of different developmental stages.

The tadpole ovaries at TK stage XIX can synthesize and secrete estradiol (E2), yet it is unknown when this ovarian function starts and how it develops. To this end, the present work has been carried out. The ovaries of different developmental stages of tadpoles and young frogs of Rana catesbeiana were taken, cut into small pieces, and incubated for 6 hr at 20 degrees in Krebs-Ringer bicarbonate buffer. The media were then analyzed for E2 by radioimmunoassay. The results indicate that the tadpoles synthesize and release E2 as early as stage X, that E2 increases slowly and gradually through stage XXV, and that E2 increases rapidly in juvenile frogs. This trend of growth of the ovarian function in estradiol secretion in vitro is in accordance with that reported for female chick embryos. There exists the possibility that the growth of E2 secretion could be biphasic, one with slow increment of autonomous E2 secretion at early stages and the other with quick increase due to pituitary stimulation at the stage of metamorphic climax.

Analysis of Variance↗
PubMed1985

Molecular basis of an inherited retinal defect in Drosophila.

Fruitflies carrying the autosomal recessive mutation transient receptor potential (trp) are blind in bright light because the receptor potential of such a mutant decays almost completely during an intense stimulus. The trp gene has been localized and a set of partially overlapping genomic clones that include the trp gene has been isolated. The stretch of DNA represented by these genomic clones is found to contain genes that encode for four RNA species. Two of these RNA species are missing in the mutant. This observation is consistent with the notion that the mutation alters the DNA sequence in a region containing signals necessary for the expression of the gene. Accordingly, the molecular basis of the mutant phenotype may be due to the lack of a protein(s) that is/are important for normal visual transduction.

Animals↗
PubMed1981

Recovery of coliphages from wastewater effluents and polluted lake water by the magnetite-organic flocculation method.

A magnetite-organic flocculation method was developed for the concentration of coliphages from wastewater effluents and polluted lake water. A high percent (68 to 100%) recovery of coliphages from sewage effluents was achieved by this procedure. Coliphage recovery from Lake Alice, a sewage-contaminated lake, showed phage concentrations ranging from 2.3 X 10(2) to 1.9 X 10(3) plaque-forming units per liter. This method is simple and inexpensive and may be carried out under field conditions.

Coliphages↗
PubMed1981

Positively charged filters for virus recovery from wastewater treatment plant effluents.

Positively charged Zeta Plus filters were used to concentrate enteroviruses from 19 liters of effluent from activated sludge units. Neither the addition of salts nor the acidification of the effluent was required for adsorption of viruses to the filters. Viruses adsorbed to the filters were eluted by treating the filters with a solution of 4 M urea buffered at pH 9 with 0.05 M lysine. Eluted viruses were concentrated into final volumes of 1 to 2 ml by using a two-step concentration procedure that employed inorganic and organic flocculation. Approximately 50% of the viruses added to effluents could be recovered in the final sample. The procedure was used to monitor effluents from activated sludge units at two wastewater treatment plants for the presence of enteroviruses.

Enterovirus↗
PubMed1979

Whole-body single-photon emission computed tomography using dual, large-field-of-view scintillation cameras.

A whole-body single-photon emission computed tomography system (SPECT) consisting of two large-field-of-view scintillation cameras mounted on a rotatable gantry, a minicomputer and a display station has been designed, constructed and evaluated. In its usual mode of operation, eleven contiguous transverse sections, each 12.5 or 25 mm thick, are reconstructed from projection data acquired during a single, continuous 360 degree rotation lasting from 2 to 22 min. A generalised filtered and weighted backprojection algorithm is used to reconstruct data obtained with conventional parallel-hole collimators in the case of body scanning, or with specially designed fan beam collimators in the case of centrally positioned organs. A simple, yet effective, correction is used to compensate for the effects of gamma ray attenuation within the patient. In addition to providing transverse section images, the system is capable of simultaneous acquisition of opposed conventional scintigrams, the reconstruction of longitudinal section images, and the acquisition of gated cardiac transverse sections. Resolutions in the reconstructed images are typically 15 mm for body scans and 11 mm for brain scans, with only slight variations in sensitivity and resolution within the image. Phantoms and clinical data demonstrate that the SPECT system generates high quality section images while maintaining most of the flexibility of normal scintillation cameras, with the added advantage of dual heads.

Tomography, Emission-Computed↗
PubMed1976

Marked suppression of thyroid function in rats with gram-negative septicemia.

Gram-negative septicemia was induced in rats by two daily injections of fecal mixture into the thigh, after which the thyroid function was markedly suppressed for 2 days. Iodine metabolism was studied by organ radioassay and by imaging with a multiwire proportional chamber (MWPC) at various time intervals after intravenous injection of 125I. Plasma T3, T4, and TSH, measured by radioimmunoassays, were suppressed, as were the T3-resin uptakes. Fractional blood supply to the thyroid glands of the infected rats, studied by the 81Rb uptake method, was also found to be markedly reduced. Sections of the thyroid glands showed little structural change during the period of marked thyroid suppression. There was no biochemical evidence of renal failure in the septicemic rats.

Animals↗
PubMed1975

An unstable strain of Aspergillus foetidus segregating proline auxotrophs.

Two basic colony types have been obtained through single conidial isolation from the Bode strain of Aspergillus foetidus as well as from mutants of this unstable strain. Type I is prototrophic whereas type II is an auxotroph requiring proline. When a type I strain is grown on complex medium it gradually becomes overwhelmed by type II sectors of growth. However, essentially pure cultures of type I can be maintained on minimal medium (lacking proline). The yield of glucoamylase from type II cultures is less than half that obtained with type I cultures. The instability of type I cultures when grown on complex medium can not be explained by heterokaryosis or the presence of virus-like particles found in the original Bode strain and its derivatives. The isolation of five stable prototrophic strains obtained as more rapidly growing sectors from type I subcultures grown on complex medium suggests that the instability most probably results from a duplicated chromosomal segment or other chromosomal aberration analogous to those described in A. nidulans.

Aspergillus↗
PubMed1973

Intergenic complementation of glucoamylase and citric acid production in two species of Aspergillus.

All auxotrophs of Aspergillus foetidus and all but two auxotrophs of A. niger which we isolated yield glucoamylase and citric acid, respectively, at levels below that of the prototrophic strain from which they were derived. Results of representative heterokaryon tests suggest that the nucleus was principally responsible for the inheritance of citric acid or glucoamylase production. Most somatic diploid strains of A. foetidus gave rise to higher yields of glucoamylase when compared to their haploid component strains. Both heterokaryons and somatic diploid strains of A. niger synthesized between auxotrophs which were simultaneously reduced in citric acid yields also gave rise to enhanced yields when compared with their haploid components. The yields of a heterokaryon and somatic diploid synthesized between two high producers of citric acid were not higher than those of respective haploid components. We concluded from these results that gene dosage (or ploidy) does not increase the yield of citric acid. The apparent enhancement in yields observed in diploids or heterokaryons synthesized between auxotrophs with reduced yields in both species can be interpreted as resulting from intergenic complementation.

Amino Acids↗