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Biomedical subjects

S Chang

Publications and source records attributed to S Chang.

At least 325 records · Page 18Linked to original sources
PubMed1989

Perfluorocarbon liquids in the management of traumatic retinal detachments.

Low viscosity perfluorocarbon liquids were used as an intraoperative tool during vitrectomy for retinal detachment (RD) after penetrating ocular trauma. These liquids are immiscible with water and have specific gravities from 1.8 to 1.9. Intraoperatively, the perfluorocarbon liquids flattened the retina in 14 eyes by displacing the subretinal fluid through peripheral breaks. Posterior retinotomy was not required for internal drainage of subretinal fluid. Pooled subretinal fluid was displaced from the macular area in five patients. The perfluorocarbon bubble mechanically stabilized the retina during epiretinal membrane dissection. The perfluorocarbon liquid was removed and replaced perfluorocarbon gas or silicone oil. In 11 patients followed for more than 6 months after the final surgery, eight (73%) eyes were anatomically successful, with six (54.5%) gaining visual acuity of 20/400 or better.

Adolescent↗
PubMed1989

Methionine aminopeptidase gene of Escherichia coli is essential for cell growth.

We localized the methionine aminopeptidase (map) gene on the Escherichia coli chromosome next to the rpsB gene at min 4. Genetically modified strains with the chromosomal map gene under lac promoter control grew only in the presence of the lac operon inducer isopropyl-beta-thiogalactoside. Thus, methionine aminopeptidase is essential for cell growth.

Aminopeptidases↗
PubMed1988

Cloning, characterisation and regulation of an alpha-amylase gene from Streptomyces venezuelae.

The alpha-amylase gene (aml) of Streptomyces venezuelae ATCC15068 was cloned in Streptomyces lividans TK24 using the plasmid vector pIJ702. Sub-cloning and exonuclease III deletion experiments localised the sequences required for alpha-amylase production to a segment of 2.05 kb. Low-resolution nuclease S1 mapping revealed a aml transcript of approx. 1.7 kb, and the extracellular form of alpha-amylase was estimated by SDS-polyacrylamide gel electrophoresis to be 59 kDa, suggesting that aml mRNA is monocistronic. The nucleotide sequence of aml was determined and high-resolution nuclease S1 mapping experiments identified transcripts that appeared to initiate at a promoter identical to that of the alpha-amylase gene of Streptomyces limosus [Long et al., J. Bacteriol. 169 (1987) 5745-5754]. Transcription of aml in S. venezuelae, and of the cloned gene in Streptomyces coelicolor A3(2), was induced by maltose and repressed by glucose. Glucose repression in S. coelicolor A3(2) depended on a functional glucose kinase gene. The predicted amino acid sequence of the extracellular enzyme was very similar (75% identity) to the alpha-amylase of S. limosus and shared with this enzyme a strong susceptibility to tendamistat, a potent inhibitor of mammalian alpha-amylases. Sequence inspection revealed a putative signal sequence of 28 amino acids that preceded the probable signal peptidase cleavage site.

Amino Acid Sequence↗
PubMed1988

Intraoperative perfluorocarbon liquids in the management of proliferative vitreoretinopathy.

Three low-viscosity perfluorocarbon liquids were used intraoperatively for hydrokinetic manipulation of the retina during vitreous surgery for retinal detachment with advanced proliferative vitreoretinopathy. All 23 patients had massive proliferative vitreoretinopathy (Grade D, Retina Society classification), and 16 (69.6%) had Grade D-3 with a closed-funnel configuration. In 21 eyes the retina could be flattened intraoperatively by perfluorocarbon liquids without requiring posterior retinotomy for internal drainage of subretinal fluid. The temporary mechanical fixation of the retina provided by this tool facilitated the removal of epiretinal membranes and release of traction. Fifteen eyes (65.2%) maintained long-term retinal reattachment with follow-up of six months or more. These liquids are useful adjuncts in the management of retinal detachment with severe proliferative vitreoretinopathy.

Adolescent↗
PubMed1988

The nature and origin of interstellar diamond.

Microscopic diamond was recently discovered in oxidized acid residues from several carbonaceous chondrite meteorites (for example, the C delta component of the Allende meteorite). Some of the reported properties of C delta seem in conflict with those expected of diamond. Here we present high spatial resolution analytical data which may help to explain such results. The C delta diamond is an extremely fine-grained (0.5-10 nm) single-phase material, but surface and interfacial carbon atoms, which may comprise as much as 25% of the total, impart an 'amorphous' character to some spectral data. These data support the proposed high-pressure conversion of amorphous carbon and graphite into diamonds due to grain-grain collisions in the interstellar medium although a low-pressure mechanism of formation cannot be ruled out.

Carbon↗
PubMed1988

An epimerase-reductase in L-fucose synthesis.

The first committed enzyme in GDP-L-fucose formation from GDP-D-mannose is GDP-D-mannose 4,6-dehydratase, which forms GDP-4-keto-6-deoxy-D-mannose. The uncertain enzymatic steps beyond this point were examined in this study. Assays were developed for the epimerase and reductase activities which the putative pathway would predict. A protein was isolated exhibiting homogeneity by several criteria. This single protein, which forms GDP-L-fucose from GDP-4-keto-6-deoxy-D-mannose and NADH, appears to possess both epimerase and reductase capabilities and may be termed GDP-4-keto-6-deoxy-D-mannose-3,5-epimerase-4-reductase. Analysis on a molecular sieve column using fast protein liquid chromatography established a molecular weight of 63,100 for the native enzyme, whereas sodium dodecyl sulfate-polyacrylamide gel electrophoresis established a subunit molecular weight of 31,500.

Animals↗
PubMed1988

Laboratory investigations of Mars: chemical and spectroscopic characteristics of a suite of clays as Mars soil analogs.

Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils.

Aluminum Silicates↗
PubMed1988

Deuterium exchange during acid-demineralisation.

Isotopic analyses of residues prepared by demineralisation of the Murchison meteorite using D-labelled reagents provide evidence for measurable exchange of H-isotopes between residue and reagents. Precise quantification of this effect is precluded by substantial inhomogeneity of the meteoritic organic matter. A conservative estimate of the degree of exchange is 3 to 5% of the H pyrolysable as H2O. This could affect the shape of the curve defining D-release as a function of temperature, but does not change conclusions previously drawn concerning the nature of the bulk D-enrichment of insoluble organic matter in meteorites.

Astronomical Phenomena↗
PubMed1988

Leukotrienes levels in the aqueous humor following experimental ocular trauma.

Using radioimmunoassay technique, levels of leukotriene B4 and C4 (LTB4 and LTC4) in the aqueous humor of rabbit eyes were measured following experimental nonpenetrating ocular trauma. Slit lamp examination showed a time-dependent increase of flare, cells, and fibrin in the anterior chamber of the traumatized eyes. Polymorphonuclear (PMN) leukocyte influx into the aqueous humor was not seen at 6 hours but increased significantly in traumatized eyes after 12 hours. No inflammatory cells were observed in control eyes. Histopathologic studies demonstrated injuries of the ciliary body, ruptures of the retina and choroid, with intraocular hemorrhage. LTB4 values peaked at 6 hours, prior to PMN cell infiltration and remained significantly higher than controls, which remained undetectable at all intervals after injury. LTC4 values also peaked by 6 hours in the traumatized eyes. These data demonstrate that elevations in LTB4 and LTC4 are associated with blunt trauma, and this precedes PMN cell infiltration. Leukotrienes may play a role in the early inflammatory response following concussive ocular injuries.

Animals↗
PubMed1988

A biologic tissue adhesive for vitreoretinal surgery.

Commercially available tissue glue was injected subretinally under mechanically induced retinal detachments in rabbit eyes resulting in chorioretinal adhesions at the injection site. After serial enucleation all eyes underwent histologic evaluation. Results were encouraging, but pooled fibrinogen is not acceptable for human use. A substitute for the pooled fibrinogen fraction, an adhesive using autologous plasma was prepared and studied after subretinal and intravitreal injection into rabbit and pig eyes. Postoperative clinical follow-up was one year for the rabbit eyes and one month for the pig eyes, after which all globes were enucleated. Histopathologic evaluation demonstrated circumscribed chorioretinal adhesions at the injection site. The autologous bioadhesive was applied as an adjunct in vitreoretinal surgery over macular holes and large retinal tears. As it is relatively short acting (ie, 4-6 days), it may be considered as a possible addition to existing techniques, facilitating difficult surgical procedures.

Adult↗
PubMed1988

Planetary environments and the conditions of life.

Life arose on Earth within a billion years (1 Ga) after planetary accretion and core formation. The geological record, which begins 3.8 Ga BP, indicates environmental conditions much like today's, except for the absence of oxygen. By 3.5 Ga BP microbial ecosystems were already colonizing shallow marine hydrothermal environments along shorelines of volcanic islands. Although similar environments could have existed more than 3.8 Ga BP, they may not have been the spawning grounds of life. Geophysical models of the first 600 Ma of Earth history following accretion and core formation point to a period of great environmental disequilibrium. In such an environment the passage of energy from Earth's interior and from the Sun through gas-liquid-solid domains and their boundaries with each other generated a dynamically interacting, complex hierarchy of self-organized structures, ranging from bubbles at the sea-air interface to tectonic plates. Nested within this hierarchy were the precursors of living systems. The ability of a planet to produce such a hierarchy is speculated to be a prerequisite for the origin and sustenance of life. Application of this criterion to Mars, which apparently experienced no plate tectonism, argues against the origin of martian life. Because only further geological and biogeochemical exploration of the planet can place these qualitative speculations on firm ground, the search for evidence of extinct life on Mars continues to be of highest scientific priority.

Biological Evolution↗
PubMed1988

Brain norepinephrine: a possible role in bronchial asthma.

The purpose of this study was to evaluate the relationship between neuroendocrine function and the beta receptor activity of the lung in a group of 47 pediatric patients with bronchial asthma. It is postulated that since hypothalamic norepinephrine (NE) is known to inhibit corticotropin-releasing hormone (CRH), an increase in brain NE as measured by its metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) could reflect the depression of the hypothalamic-pituitary-adrenal (HPA) axis as measured by urinary cortisol levels. Further, since cortisol influences epinephrine formation in the adrenal medulla and since cortisol and epinephrine contribute to beta receptor function, it is further postulated that an increase in brain NE by depressing the HPA axis could thereby, cause a relative decrease in both cortisol and epinephrine with resultant beta receptor dysfunction. In both age groups, the 3- to 11-year-olds and the adolescents, differences in NE were found among the three subgroups (P = .003) with the difference observed only between the wheezing (decreased NE) and control groups (P less than .05). There was a similar difference in MHPG (elevated) among these groups. In a similar manner, the MHPG/NE ratios (elevated) were statistically different in comparing the three groups in the 3- to 11-year-old range. In the adolescent group both the wheezing and nonwheezing groups were comparably elevated and showed statistically significant differences from their controls. The results of this study appear to support the hypothesis and suggests that brain NE may play a pivotal role in the beta-adrenergic dysfunction characteristic of bronchial asthma.

Adolescent↗
PubMed1988

Solid-phase radioimmunoassay of human complement fragment C5a.

In this competitive RIA for determining concentrations of human C5a in biological fluids and in buffers, labeled C5a and sample are allowed to compete for binding to a limited amount of goat antibody to human C5a in solution. Free and bound tracer are then separated by a second antibody (rabbit anti-goat IgG) immobilized on paramagnetic particles. Total incubation time for this assay is 70 min. Sensitivity, precision, and analytical recovery of this assay compare well with those of a reference method.

Binding, Competitive↗
PubMed1987

Neurofascin: a novel chick cell-surface glycoprotein involved in neurite-neurite interactions.

We have identified neurofascin, a novel chick cell-surface glycoprotein involved in neurite-neurite interactions. Neurofascin is defined by its reactivity with monoclonal antibody (MAb) F6, which detects two polypeptides (160 and 185 kd) in immunotransfers of brain plasma membrane proteins. Immunoaffinity chromatography using immobilized MAb F6 yields major molecular mass bands at 185, 160, 135-110, and 92 kd. Fingerprint analyses show that these polypeptides are related. Neurofascin is expressed primarily in fiber-rich areas of embryonic cerebellum, spinal cord, and retina. Fab fragments of polyclonal antibodies to neurofascin interfere with the outgrowth of retinal and sympathetic axons in two different in vitro bioassays. Neurofascin is immunologically distinct from other known neurite-associated surface glycoproteins.

Animals↗
PubMed1987

Diagnosis of pseudoxanthoma elasticum by scar biopsy in patients without characteristic skin lesions.

Pseudoxanthoma elasticum is a disorder of connective tissue that is associated with numerous systemic complications, including accelerated atherosclerosis, gastrointestinal bleeding, angioid streaks in the ocular fundus, and blindness. Diagnosis of the disease is important because many of its complications can be prevented and genetic counseling can be offered to family members of affected patients. The purpose of this study was to examine the usefulness of scar biopsy in establishing a diagnosis of pseudoxanthoma elasticum in patients with angioid streaks but without characteristic skin lesions. Ten patients with angioid streaks but without cutaneous findings indicative of pseudoxanthoma elasticum were evaluated by biopsy of scars and flexural skin. The biopsy specimens were compared with those from unaffected controls. In 6 of the 10 patients, scar biopsies showed fragmentation and clumping of elastic tissue in the deep dermis. Three patients also had these histologic features of pseudoxanthoma elasticum in biopsy specimens of flexural skin that appeared to be normal. We conclude that biopsies of scars in randomly chosen sites may be useful when pseudoxanthoma elasticum is suspected despite the absence of typical skin lesions.

Adult↗