Search PubMed⌕ Search

Biomedical subjects

Z Liang

Publications and source records attributed to Z Liang.

At least 145 records · Page 8Linked to original sources
PubMed1994

Radon exposure in residences and lung cancer among women: combined analysis of three studies.

Lung cancer risk in relation to indoor radon was examined in three case-control studies in Stockholm (Sweden), New Jersey (United States), and Shenyang (People's Republic of China). Year-long measurements of radon gas were made in current and past homes of 966 women who developed lung cancer and of 1,158 control women, included in the combined analysis. Nearly 14 percent of the participants were estimated to have a time-weighted, mean, radon concentration in their homes of more than 4 pCi/l (150 Bq/m3) during the period from five to 35 years prior to the date of lung cancer diagnosis (or comparable date for controls). There was a tendency for risk to increase with increasing levels of radon in NJ and Stockholm, but the trends for individual studies and overall were not statistically significant. The estimates of the excess relative risk for indoor exposure per pCi/l were 0.18 (95 percent [CI] = -0.04-0.70) in NJ, 0.06 (CI = -0.05-0.34) in Stockholm, and -0.02 (CI = -infinity-0.03) for Shenyang; these estimates did not differ significantly from each other. The overall excess RR per pCi/l was 0.00 (CI = -0.05-0.07); the confidence limits were sufficiently broad, however, that the overall estimate was still compatible with extrapolations of risks from miners. Cigarette smoking was the predominant cause of lung cancer with the RR significantly elevated in all studies. Within smoking categories, the trend in risk with increasing mean radon concentration was inconsistent. Analyses of data from several studies are complicated by the possibility that there may exist important differences in study bases which might affect results, and which may be controlled only partially through adjustment procedures. Future efforts to combine various residential studies will need to be attentive to the intrinsic limitations of studies to detect low levels of risk as well as the unique uncertainties associated with estimating, accurately, cumulative exposure to indoor radon.

Adult↗
PubMed1994

Enhancer trapping by a human mid-sized neurofilament transgene reveals unexpected patterns of neuronal enhancer activity.

In ten transgenic lines, expression of a human mid-sized (M) neurofilament (NF) transgene was restricted to neurons in the central and peripheral nervous systems. However, no two lines gave identical expression patterns and none exactly matched the expression of mouse NF(M). These varied expression patterns within the neural compartment likely result from interactions of the transgene with enhancer elements located in the regions flanking the insertion site. Unexpected patterns of enhancer activity included an enhancer active in subsets of cerebellar basket cells as well as others preferentially active in subsets of motor or sensory neurons.

Amino Acid Sequence↗
PubMed1994

An analytical approach to quantitative reconstruction of non-uniform attenuated brain SPECT.

An analytical approach to quantitative brain SPECT (single-photon-emission computed tomography) with non-uniform attenuation is developed. The approach formulates accurately the projection-transform equation as a summation of primary- and scatter-photon contributions. The scatter contribution can be estimated using the multiple-energy-window samples and removed from the primary-energy-window data by subtraction. The approach models the primary contribution as a convolution of the attenuated source and the detector-response kernel at a constant depth from the detector with the central-ray approximation. The attenuated Radon transform of the source can be efficiently deconvolved using the depth-frequency relation. The approach inverts exactly the attenuated Radon transform by Fourier transforms and series expansions. The performance of the analytical approach was studied for both uniform- and non-uniform-attenuation cases, and compared to the conventional FBP (filtered-backprojection) method by computer simulations. A patient brain X-ray image was acquired by a CT (computed-tomography) scanner and converted to the object-specific attenuation map for 140 keV energy. The mathematical Hoffman brain phantom was used to simulate the emission source and was resized such that it was completely surrounded by the skull of the CT attenuation map. The detector-response kernel was obtained from measurements of a point source at several depths in air from a parallel-hole collimator of a SPECT camera. The projection data were simulated from the object-specific attenuating source including the depth-dependent detector response. Quantitative improvement (>5%) in reconstructing the data was demonstrated with the nonuniform attenuation compensation, as compared to the uniform attenuation correction and the conventional FBP reconstruction. The commuting time was less than 5 min on an HP/730 desktop computer for an image array of 1282*32 from 128 projections of 128*32 size.

Brain↗
PubMed1994

Quantitative reconstruction for myocardial perfusion SPECT: an efficient approach by depth-dependent deconvolution and matrix rotation.

An efficient reconstruction method for myocardial perfusion single-photon emission computed tomography (SPECT) has been developed which compensates simultaneously for attenuation, scatter, and resolution variation. The scattered photons in the primary-energy-window measurements are approximately removed by subtracting the weighted scatter-energy-window samples. The resolution variation is corrected by deconvolving the subtracted data with the detector-response kernel in frequency space using the depth-dependent frequency relation. The attenuated photons are compensated by recursively tracing the attenuation factors through the object-specific attenuation map. An experimental chest phantom with defects inside myocardium was used to test the method. The attenuation map of the phantom was reconstructed from transmission scans using a flat external source and a high-resolution parallel-hole collimator of a single-detector system. The detector-response kernel was approximated from measurements of a point source in air at several depths from the collimator surface. The emission data were acquired by the same detector setting. A computer simulation using similar protocols as in the experiment was performed. Both the simulation and experiment showed significant improvement in quantification with the proposed method, as compared to the conventional filtered-backprojection technique. The quantitative gain by the additional deconvolution was demonstrated. The computation time was less than 20 min on a HP/730 desktop computer for reconstruction of a 1282 x 64 array from 128 projections of 128 x 64 samples.

Algorithms↗
PubMed1994

[Preparation and antigenic characterization of rat monoclonal antibodies against hemorrhagic fever with renal syndrome virus].

11 hybridoma cell lines secreting monoclonal antibodies (McAbs) against hemorrhagic fever with renal syndrome virus (HFRSV) were obtained in our laboratory by immunizing LOU/C rats with HFRSV Chen strain. These rat McAbs were characterized by radio-immunoprecipitation and western blotting methods, 2 directed against glycoprotein G2, 9 against nucleocapsid protein (NP) of HFRSV. The results of neutralization (NT) and hemagglutination inhibition(HI) test showed that most of the McAbs specific for NP had neither NT nor HI activities, but 2 had obvious NT and/or HI activities. It was suggested that there may be some neutralizing and hemagglutinating determinants on NP of HFRSV. Two McAbs to G2 had HI or/and NT activities. These date indicated that distinct neutralizing and hemagglutinating epitopes were located on the G2. Comparative antigenic analysis of 20 strains of HFRSV was carried out by immune horseradish peroxidase technique using 11 anti-HFRSV rat McAbs. It was found that these McAbs can be classified into group, subgroup, apodemus type and subtype specificity to HFRSV.

Animals↗
PubMed1994

On the measurement of naturalization.

This paper proposes a new way of measuring naturalization, which takes into account both emigration and death. I argue that the new method corrects for underestimation and thus provides a more accurate measure of the concept. Using data from six groups of the 1973 immigrant cohort and multiple-decrement life table techniques, I estimated and compared naturalization measures derived from new and old methods. The results show that failure to control for emigration has a significant effect on the measurement of naturalization, particularly if an immigrant group has relatively high rate of emigration. Some further substantive implications of this new method are also explored.

Acculturation↗
PubMed1994

Fusion expression vectors for recombinant gene products processed easily and purified rapidly by affinity chromatography.

A DNA fragment encoding IgG-binding domain B,C (PABC) was separated from protein A gene, cloned into phage M13 and modified by oligo-directed mutagenesis at the hydroxylamine-cleaved site from Asn-Gly to Asn-Ala in domain B and C, respectively. The modified PABCm gene fragment was used to construct one set of fusion expression vectors in different reading frames. Processing sequences such as those recognized by enterkinase, collagenase, thrombin, activated factor X and cleaved by the hydroxylamine, N-chlorosuccinimide etc. can be created in the fusion site. Using the above vectors, fusion proteins such as PABCm-IGF-I, -hGRF, -bGRF and their derivatives were highly expressed in E. coli. The yield of fusion proteins is over 100 mg per liter cultured by analysis of SDS-PAGE. The PABC fusion proteins can be rapidly purified by the affinity chromatography with a IgG-sepharose column.

Base Sequence↗
PubMed1993

Proton transfer in the catalytic mechanism of carbonic anhydrase. Effects of placing histidine residues at various positions in the active site of human isoenzyme II.

The maximal rate of CO2 hydration catalyzed by human carbonic anhydrase II (carbonate hydro-lyase, EC 4.2.1.1) is limited by proton transfer steps involving the acid-base function of His-64. To test whether or not the precise location of this proton transfer group is critical, histidine residues were placed in various positions in the active site of the enzyme. Thus, four double mutants were made, all with His-64 replaced by Ala-64, and with a histidine residue replacing Asn-62, Ala-65, Asn-67 or Thr-200. The results show that the mutants with His-62, His-67 and His-200, but not the mutant with His-65, yield significantly higher kcat values for CO2 hydration than the single mutant with Ala-64, indicating that His-62, His-67 and His-200 can contribute to proton transfer between the metal center and the reaction medium. However, the average proton transfer efficiency of these histidines is only about 5% of that of His-64 in the unmodified enzyme.

Binding Sites↗
PubMed1993

Importance of the conserved active-site residues Tyr7, Glu106 and Thr199 for the catalytic function of human carbonic anhydrase II.

The catalytic mechanism of carbonic anhydrase includes the reaction of a zinc-bound hydroxide ion with the CO2 substrate. This hydroxide ion is part of a hydrogen-bonded network involving the conserved amino acid residues Thr199, Glu106 and Tyr7. To investigate the functional importance of these residues, a number of site-specific mutants have been made. Thus, Thr199 has been changed to Ala, Glu106 to Ala, Gln and Asp, and Tyr7 to Phe. The effects of these mutations on catalyzed CO2 hydration and ester hydrolysis have been measured, as well as the binding of some inhibitors. The results show that the CO2 hydration activity of the mutant with Phe7 is only marginally reduced, whereas the esterase activity is larger than that of unmodified enzyme. It is concluded that Tyr7 is not a functionally required element of the hydrogen-bonded network. The CO2 hydration activity (kcat as well as kcat/Km) and the esterase activity of the mutant with Ala199 are reduced about 100-fold. The affinity for the sulfonamide inhibitor, dansylamide, is only slightly reduced while the mutant has an enhanced affinity for bicarbonate and the anionic inhibitor, SCN-. The activities of the mutants with Ala106 and Gln106 are also reduced. The reduction of the esterase activity is about 100-fold, while kcat for CO2 hydration has decreased by a factor of 1000. The parameter kcat/Km is only about one order of magnitude smaller for these mutants than for the unmodified enzyme. The binding of dansylamide and another sulfonamide inhibitor, acetazolamide, are about 20-times weaker to the mutant with Gln106 than to unmodified enzyme. These results suggest important roles for Thr199 and Glu106 in carbonic anhydrase catalysis. The mutant with Asp106 is almost fully active suggesting that the structure has undergone a compensatory change to maintain the interaction between residue 106 and Thr199.

Amino Acid Sequence↗
PubMed1993

Trend of change in various kinds of nuclear families in China since the 1980s.

"By using the latest data of 1% sampled data made in the Fourth Population Survey in 1990 and 1 [per 1,000], sampled data made in the Third Population Survey in 1982, we have attempted an analysis...of the trend of change of proportion among nuclear parents-families, separated-parents, single-parent and interval-generation families, as well as two-, three- and four-generation lineal and joint families in China during the 1980s, both as a nation and in all provinces, municipalities directly under the central government and autonomous regions."

Asia↗
PubMed1993

[Experimental research of acupuncture manipulation of reinforcing and reducing by lifting and thrusting needle on the animal].

The experiment were performed on model rabbits injected with large dosage of Dexamethasone (DXM) for 5 days. Reinforcing manipulation (RIM), reducing manipulation (RDM), and electric stimulation (ES) were respectively used to puncture Zusanli (ST 36) points for 5 days to observe the change on temperature, body weight, corticosterone assay, testosterone assay, and the amplitude of the plethysmogram. The result showed that there was a similar syndrome of the kidney deficiency after injecting DXM. The body weight was increased in the DXM control group, decreased in the RDM group and had no significant influence in the other groups. The body weights between the reinforcing manipulation and the reducing manipulation groups had obvious difference. But the other indices of observation had no significant influence among the different groups. So there wasn't significant difference on most of observed signs among the RIM group, the RDM group and ES group. The study of acupuncture manipulation will have yet to be further done.

Acupuncture Therapy↗
PubMed1992

Targeting of Sp1 to a non-Sp1 site in the human neurofilament (H) promoter via an intermediary DNA-binding protein.

The human neurofilament (H) promoter contains multiple binding sites for nuclear proteins including a Proximal (Prox) site centered around the sequence GGTTGGACC and an adjacent pyrimidine (Pyr) tract site centered around the sequence CCCTCCTCCCC. Surprisingly binding to a probe containing the Prox/Pyr region of the NF(H) promoter was competed in gel shifts by an oligonucleotide containing only an Sp1 binding site (GGGGCGGGG). Supershift assays with a polyclonal anti-Sp1 antisera confirmed that Sp1 was part of the complex formed with the Prox/Pyr probe. However neither bacterially expressed Sp1 516C or vaccinia virus expressed full-length Sp1 778C bound to the Prox or Pyr sequences in DNase I footprints or gel shift assays. Gel shift competitions and supershift assays with probes containing either Prox or Pyr tract sites alone demonstrated targeting of Sp1 to the Prox binding site and identified a non-Sp1 containing complex which contains a Prox binding protein. Adding exogenous Sp1 to a HeLa nuclear extract enhanced the Sp1-containing complex but had no effect on the Prox complex. These studies show that Sp1 can be targeted to a non-Sp1 site in the human NF(H) promoter through protein/protein interactions with a distinct sequence specific DNA-binding protein.

Base Sequence↗
PubMed1992

Proton transfer roles of lysine 64 and glutamic acid 64 replacing histidine 64 in the active site of human carbonic anhydrase II.

The CO2 hydration activities of cloned human carbonic anhydrase II (carbonate hydro-lyase, EC 4.2.1.1) and variants with Lys, Glu, Gln or Ala replacing His at sequence position 64 have been measured in a variety of different buffers in the pH range 6-9. The variants with Lys-64, Gln-64 and Ala-64 showed non-Michaelis-Menten behavior under some conditions, apparent substrate inhibition being prominent near pH 9. However, asymptotic Michaelis-Menten parameters could be estimated for the limit of low substrate concentrations. All variants show distinct buffer specificities, and imidazole derivatives, Ches and phosphate buffers yield higher kcat values that Bicine, Taps and Mops buffers under otherwise similar conditions. These results are interpreted in terms of different pathways for a rate-limiting proton transfer. In unmodified enzyme, the very high catalytic activity depends on His-64 functioning as an efficient proton transfer group, but this pathway is not available in the variants with Gln-64 and Ala-64. Imidazoles, Ches and phosphate are thought to participate in a metal center-to-buffer proton transfer pathway, whereas Bicine, Taps, Mops and Mes appear to lack this capacity, so that the rate-limiting proton transfer occurs in a metal center-to-bulk water pathway for these variants. The Lys-64 and Glu-64 variants give significantly higher kcat values in Taps, Mops and Mes buffers than the Ala-64 and Gln-64 variants. The pH dependencies of these kcat values are compatible with the hypothesis that Lys-64 and Glu-64 can function as proton transfer groups. Thus, at pH near 9, Lys-64 appears to be only 5-times less efficient than His-64, while Glu-64 is inefficient. At pH 6, Lys-64 is an inefficient proton transfer group, but Glu-64 is only 2-3-times less efficient than His-64. The data indicate that Lys-64 and Glu-64 have pKa values near 8 and below 6, respectively.

Binding Sites↗
PubMed1992

Background correction by wavelength modulation for pulsed-laser-excited atomic fluorescence spectrometry.

Instrumentation was constructed to modulate the dye laser wavelength for background correction in laser-excited atomic fluorescence spectrometry (LEAFS). To achieve wavelength modulation a piezoelectric pusher was used to drive the wavelength tuning mirror in a laboratory-constructed grazing incidence dye laser. The laser pulses were synchronized with the piezoelectric pusher movement so that alternate laser pulses measured the atomic fluorescence signal at the analytical atomic spectral line (on-line) and the background signal at a wavelength displaced to one side of the atomic line (off-line). The background-corrected signal was obtained by subtracting the off-line "background" from the on-line "signal plus background". The spectral line width (fwhm) of the dye laser was 0.003 nm, while the wavelength modulation interval was controllable over the range from 0 to 0.2 nm with a spectral resolution limited only by the spectral line width of the laser. This type of background correction could, in principle, be applied to other types of tunable lasers such as pulsed Ti: sapphire lasers. The performance of background correction by wavelength modulation (WM) was demonstrated by measurement of sodium resonance fluorescence in an air-acetylene flame and by thallium nonresonance fluorescence in a graphite furnace. The experimental data indicated that the wavelength modulation corrected, effectively and quantitatively, for flame background, blackbody emission from a graphite furnace, and scatter of laser radiation off aluminum chloride (1 mg/mL as AI) matrix particles in both the furnace and the flame. Analytical results were in good agreement with certified values for the determination of sodium in standard reference materials by the use of modulated LEAFS.

Lasers↗
PubMed1992

Expression of human mid-sized neurofilament subunit in transgenic mice.

We have created transgenic mice which carry and express the gene encoding the human NF(M) subunit. RNAase protection assays reveal that the transgene is abundantly expressed in CNS and PNS but also, at very low levels in some non-neural tissues as well. Although the neurospecificity of transgene transcription was not absolute, we are able to detect the protein only in neurons with immunocytochemical techniques. Glial and endothelial cells do not contain immunoreactive materials. Interesting subtle differences in the relative level of the human transgene encoded and endogenous murine encoded NF(M) proteins were noted in different regions of the brain. Similar differences were found in the levels of transgene and endogenous gene mRNA suggesting that these differences may be traceable to differences in RNA transcription or stability. Our data demonstrate, within the sensitivity of the immunocytochemical techniques we used, that the human NF(M) protein is present only in the neurons of the transgenic mice and that it is present in the same neurons as the endogenous NF(M). Furthermore, immunoelectron-microscopic examination of isolated neurofilaments shows that the human NF(M) coassembles with the endogenous NF(M) during filament formation. Thus, although the human NF(M) possesses a much larger multiphosphorylation site in its carboxy terminus, it seems to be the functionally equivalent to the mouse protein, even in the murine neuron.

Animals↗
PubMed1992

Novel DNA binding proteins participate in the regulation of human neurofilament H gene expression.

By a combination of DNase I footprinting, methylation interference, and gel shift analyses we have identified multiple binding sites for nuclear proteins within the promoter region of the human neurofilament H gene. Two sites likely bind the transcription factor Sp1 while two others may be targets for previously unrecognized DNA binding proteins. One site, PAL, occurs within the 10 bp sequence GGGGAGGAGG. Two copies of the PAL sequence form an interrupted palindrome around one of the Sp1 sites. A second site, PROX, is found within the sequence GGTTGGACC. Nuclear extracts prepared from both neural and non-neural cell lines, mouse brain, and mouse liver contain proteins that recognize and bind to the PROX and PAL sequences indicating that proteins which bind to these target sequences are widespread. The appearance of these target sequences in the 5' upstream region of several neuron specific genes suggests that they play key roles in the transcription of neuron specific genes. The functional activity of these target DNA sequences was demonstrated by transfection assays using a reporter gene fused to nested deletions of the NF(H) promoter region. Interestingly, these assays revealed that maximal transient expression was obtained with DNA fusion genes containing the PAL, PROX and TATA sequences. Inclusion of the Sp1 sites into the fusion genes failed to enhance the expression of the reporter gene. To determine if the NF(H) promoter can be activated in a tissue specific manner during development transgenic mice containing the promoter region linked to a beta-galactosidase reporter gene were generated. In one line sporadic expression of the transgene occurred in the CNS and testis while in four other lines no expression occurred. Collectively these results suggest that the NF(H) gene promoter is active in a tissue specific manner only by interactions with regulatory elements that lie further upstream or downstream of the start site of initiation.

Animals↗
PubMed1992

Multiple nuclear factors interact with the promoter of the human neurofilament M gene.

In order to identify potential regulatory elements of the human mid-sized (M) neurofilament (NF) gene we preformed DNase I footprinting, gel mobility shift assays and methylation interference studies with probes from the NF(M) immediate 5' flanking region. These studies identified multiple sites for DNA-binding proteins including four Sp1 sites, and single sites each for members of the NF-1 and AP-1 families of DNA binding proteins. In addition a binding site within a pyrimidine tract likely binds a novel DNA-binding protein which also interacts with the human NF(H) gene promoter. Factors that bind to these sites are found in both neural and non-neural cells suggesting that the NF(M) promoter may not contain tissue specific regulatory signals. In transient assays, addition of these binding sites to an NF(M) minimal promoter containing only a TATA box lead to a greater than 40-fold activation of transcription over background. Progressive 5' deletions reduced expression in a step wise manner suggesting that all the factors likely act synergistically as positive regulators of transcription.

Base Sequence↗