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Biomedical subjects

C Y Tang

Publications and source records attributed to C Y Tang.

At least 19 recordsLinked to original sources
PubMed1997

Gypsy retrotransposon as a tool for the in vivo analysis of the regulatory region of the optomotor-blind gene in Drosophila.

We report here a method for the in vivo dissection of the regulatory region of a gene in the Drosophila genome. Our system includes (i) the reporter genes lacZ and white to detect transcriptional enhancer and silencer activities in a target gene, (ii) an efficient way to induce integration of gypsy elements in the genome, and (iii) unidirectional blocking of regulatory activities by the gypsy element, which is dependent on the su(Hw) protein. The optomotor-blind (omb) gene was analyzed. In the omb(P1) line, a P[lacW] construct is inserted about 1.4 kb upstream of the omb transcription start site. The lacZ reporter gene within P[lacW] exhibits the same expression pattern as omb. The white reporter gene is expressed in a "bipolar" pattern. We induced high frequency gypsy mobilization in omb(P1) and identified two lines (D11 and D13-1) with altered eye pigmentation pattern, which is dependent on su(Hw) activity. A gypsy element was found inserted in the first intron of omb in D13-1 and in P[lacW] in D11. These results indicate that it is the blocking of regulatory activities by gypsy that caused the changes in the white reporter gene expression. The effect of these gypsy insertions on the expression patterns allowed us to predict several aspects of the organization of the regulatory elements in the omb locus.

Animals↗
PubMed1997

Transfer of voltage independence from a rat olfactory channel to the Drosophila ether-à-go-go K+ channel.

The S4 segment is an important part of the voltage sensor in voltage-gated ion channels. Cyclic nucleotide-gated channels, which are members of the superfamily of voltage-gated channels, have little inherent sensitivity to voltage despite the presence of an S4 segment. We made chimeras between a voltage-independent rat olfactory channel (rolf) and the voltage-dependent ether-à-go-go K+ channel (eag) to determine the basis of their divergent gating properties. We found that the rolf S4 segment can support a voltage-dependent mechanism of activation in eag, suggesting that rolf has a potentially functional voltage sensor that is silent during gating. In addition, we found that the S3-S4 loop of rolf increases the relative stability of the open conformation of eag, effectively converting eag into a voltage-independent channel. A single charged residue in the loop makes a significant contribution to the relative stabilization of the open stage in eag. Our data suggest that cyclic nucleotide-gated channels such as rolf contain a voltage sensor which, in the physiological voltage range, is stabilized in an activated conformation that is permissive for pore opening.

Amino Acid Sequence↗
PubMed1995

Conserved cysteine residues in the shaker K+ channel are not linked by a disulfide bond.

Many voltage-activated K+ channels contain two conserved cysteine residues in putative transmembrane segments S2 and S6. It has been proposed that these cysteines form an intrasubunit disulfide bond [Guy, H.R., & Conti, F. (1990) Trends Neurosci. 13, 201-206]. This proposal was tested using site-directed mutagenesis followed by electrophysiological and biochemical analysis of the Shaker B K+ channel. Each Shaker B subunit contains seven cysteine residues, including the conserved residues C286 and C462 and a less conserved cysteine, C245. Each cysteine in the Shaker B protein can be mutated individually without eliminating functional activity, indicating that the protein does not contain a disulfide bond that is essential for protein folding or the assembly of active channels. To determine whether there is a nonessential disulfide bond, Shaker B protein was subjected to limited proteolysis. Fragments were analyzed by electrophoresis under reducing and nonreducing conditions followed by immunoblotting. The results indicate that the two conserved residues C286 and C462 do not form a disulfide bond with each other or with C245. In addition, the subunits are not linked by disulfide bonds. In HEK293T cells, Shaker B protein is first made as an incompletely glycosylated precursor that is converted to the fully glycosylated mature protein. Glycosylation occurs at two positions in the S1-S2 loop.

Amino Acid Sequence↗
PubMed1995

Weight of edged lenses in different eyewire shapes and sizes.

Weights of edged lenses in different eyewire shapes and sizes were studied through mathematically generated eyewire shapes. The patterns of weight variation are often regular and predictable. The relation of lens weight changes in neighbouring sizes of a given eyewire shape and that in different boxed vertical lens dimensions of a given general eyewire appearance were established. These results were verified with physically edged lenses. Through these relations, it will be possible to predict the amount of weight change in a pair of spectacles upon changing the frame size and in some cases of eyewire shape modification.

Equipment Design↗
PubMed1993

Weight of edged spherical lenses in simulated eyewire shapes.

Eyewire shapes of some currently available spectacle frames were constructed mathematically and weights of spherical lenses cut to these shapes were computed for different decentrations in three commonly used lens materials. The results confirm a previous observation that the edged shape of a negative lens has only a minor effect on its weight, although this is often not the case for positive lenses. The appropriate diameters of circular centred lenses to be used in comparing lens weight for different materials were also examined. Relative to those adopted in previous studies, it was found that the weight of a larger lens, 58 mm diameter for negative lenses and 65 mm diameter for positive lenses, would more adequately represent the average weight of edged lenses in modern spectacle frames.

Eyeglasses↗
PubMed1992

Enzymatic instability of NADH-cytochrome b5 reductase as a cause of hereditary methemoglobinemia type I (red cell type).

Nucleotide substitutions in the gene for NADH-cytochrome b5 reductase were identified in three independent probands of hereditary methemoglobinemia type I. Patients in Kagoshima and Okinawa in Japan were shown to possess the same base change, from guanine to adenine at codon 57, which results in amino acid substitution from Arg to Gln. This nucleotide change was the same as formerly found in a patient in Toyoake, Japan (Katsube, T., Sakamoto, N., Kobayashi, Y., Seki, R., Hirano, M., Tanishima, K., Tomoda, A., Takazakura, E., Yubisui, T., Takeshita, M., Sakaki, Y., and Fukumaki, Y. (1991) Am. J. Hum. Genet. 48, 799-808). A type I patient in Italy was shown to have a base change from guanine to adenine at codon 105 which causes substitution from Val to Met. To characterize the enzymes of type I patients, Arg-57----Gln and Val-105----Met mutant enzymes were overexpressed in Escherichia coli and purified to homogeneity. kcat/Km values (NADH) of these two enzymes were 25% in Arg-57----Gln and 14.5% in Val-105----Met compared with that of the wild type enzyme, while the value of type II (generalized, severe form of the disease) mutant enzyme was 3% of the normal value (Yubisui, T., Shirabe, K., Takeshita, M., Kobayashi, Y., Fukumaki, Y., Sakaki, Y., and Takano, T. (1991) J. Biol. Chem. 266, 66-70). The type I mutant enzymes were less heat-stable and more susceptible to proteinase treatment than the wild type. From these results we conclude that restriction of enzyme deficiency to red cells in hereditary methemoglobinemia type I may be generally derived from instability and increased proteolytic susceptibility of variant NADH-cytochrome b5 reductases due to a point mutation.

Amino Acid Sequence↗
PubMed1992

Effects of monochromatic and chromatic oblique aberrations on visual performance during spectacle lens wear.

An optical system is described which allows overall visual performance to be studied when the wearer of a spectacle lens views objects through the lens periphery. Performance with lenses of any refractive power can be explored without any need for subjects to have the appropriate complementary refractive errors. In comparison with the effects of dioptric defocus, transverse chromatic aberration (TCA) is found to cause a relatively greater degradation in contrast sensitivity at high spatial frequencies when tangentially-oriented gratings are observed. The relative importance of TCA appears to have been underestimated in some previous studies. As vision is found to be affected by both TCA and defocus, a careful compromise between chromatic and monochromatic aberrations is required.

Adult↗
PubMed1990

Isoforms of chicken triosephosphate isomerase are due to specific oxidation of cysteine126.

The electrophoretic isoforms of mammalian triosephosphate isomerase (TPI; EC 5.3.1.1) are due to deamidation at two Asn-Gly sites (Asn15 and Asn71). Deamidation of these two asparagines in the subunit-subunit interface of the isologous dimer appears to destabilize the dimer and initiate degradation of the protein. Chicken TPI contains a lysine substitution for Asn71, thus precluding this deamidation site. Nevertheless, the chicken enzyme exhibits three electrophoretic isoforms. This multiplicity is not the result of deamidation of the remaining Asn15 site, but due to a specific site which is highly susceptible to oxidation. The three isoforms of chicken TPI can be reduced to a single form in the presence of high concentrations of reducing agents (e.g., greater than 15 mM dithiothreitol or greater than 50 mM 2-mercaptoethanol) and are also generated when oxidizing agents, such as oxidized glutathione, are present. The oxidized isoforms exhibit lowered catalytic activity and are more susceptible to denaturation and proteolytic degradation than the native enzyme. Structural analysis of the isoforms by chemical cleavage at the cysteine peptide bonds with 2-nitro-5-thiocyanobenzoic acid and subsequently at the methionines with CNBr followed by peptide sequencing reveals that Cys126 is the site of the modification. Since the oxidized isoforms of chicken TPI accumulate in vivo during aging analogous to the deamidated isoforms from mammals, it appears that TPI is the first example of a protein which has evolved two specific types of weak links which may initiate turnover of the protein.

Amino Acid Sequence↗
PubMed1990

The accumulation of oxidized isoforms of chicken triosephosphate isomerase during aging and development.

Triosephosphate isomerase (TPI) from mammals undergoes two specific deamidations (Asn-15 and Asn-71) which destabilize the isologous dimer and lead to the degradation of the protein. In aging cells and tissues, the deamidated isoforms accumulate apparently due to age-related changes in protein turnover. Chicken TPI lacks one of these sites (i.e., Asn 71----Lys), but also exhibits unstable isoforms. These isoforms are the result of the specific oxidations which occur both in vitro and in vivo. Electrophoretic analyses of various tissues from chicken show that the most oxidized isoform, which is present in adult tissues, is only present in small quantities in tissues of the newborn chick. Moreover, embryonic tissues contain almost exclusively the fully reduced form of TPI. Thus, it appears that oxidation rather than deamidation constitutes the first step in the degradation of avian TPI. TPI may be the first example of a protein which has evolved two different types of modifications (deamidation and oxidation) which trigger its degradation. The accumulation of both deamidated and oxidized isoforms in different species may provide clues to the underlying basis for the accumulation of modified proteins in aging.

Aging↗
PubMed1990

Thickness and weight of lenses for myopia.

High index lens materials have been introduced to minimize lens weight and thickness. By studying the best form lenses for different refractive indices and the effects of changing lens forms on thickness and weight, a method is proposed for comparing minus lenses in weight and thickness for different refractive indices and lens diameters.

Eyeglasses↗
PubMed1989

Influence of lens vertex distance changes on prismatic effect and decentration.

Changing the lens vertex distance alters the effective power of a lens, both in refractive and prismatic effect. For spherical lenses under paraxial conditions, it was found that though the amount of incorporated prism should be modified in the correcting lens in cases of vertex distance changes, the actual amount of decentration should be kept constant.

Eyeglasses↗
PubMed1989

Spherical lens decentration errors by Prentice's rule.

Sources and magnitude of errors in applying Prentice's rule in calculating decentration for spherical lenses were investigated. It was found that spherical aberration can be the only source of error in applying the rule. The overall magnitude of errors in effective prismatic effect is, however, clinically insignificant.

Eyeglasses↗
PubMed1989

[Effect of pyrethroids on rat brain synaptosomal ATPase activities].

In vitro Effect of several pyrethroids on rat brain synaptosomal ATPase activities was investigated. No significant changes in Na+, K+-ATPase and oligomycin-insensitive Mg2+-ATPase activities were observed under present experimental conditions, but all pyrethroids tested caused significant inhibition of oligomycin-sensitive Mg2+-ATPase activity with certain concentration dependence. The results suggest a possibility that pyrethroids may alter the cellular energy metabolism of the nervous system.

Adenosine Triphosphatases↗