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Biomedical subjects

H L Liu

Publications and source records attributed to H L Liu.

At least 55 records · Page 3Linked to original sources
PubMed2000

Replacement and deletion mutations in the catalytic domain and belt region of Aspergillus awamori glucoamylase to enhance thermostability.

Three single-residue mutations, Asp71-->Asn, Gln409-->Pro and Gly447-->Ser, two long-to-short loop replacement mutations, Gly23-Ala24-Asp25-Gly26-Ala27-Trp28- Val29-Ser30-->Asn-Pro-Pro (23-30 replacement) and Asp297-Ser298-Glu299-Ala300-Val301-->Ala-G ly-Ala (297-301 replacement) and one deletion mutation removing Glu439, Thr440 and Ser441 (Delta439-441), all based on amino acid sequence alignments, were made to improve Aspergillus awamori glucoamylase thermostability. The first and second single-residue mutations were designed to introduce a potential N:-glycosylation site and to restrict backbone bond rotation, respectively, and therefore to decrease entropy during protein unfolding. The third single-residue mutation was made to decrease flexibility and increase O:-glycosylation in the already highly O:-glycosylated belt region that extends around the globular catalytic domain. The 23-30 replacement mutation was designed to eliminate a very thermolabile extended loop on the catalytic domain surface and to bring the remainder of this region closer to the rest of the catalytic domain, therefore preventing it from unfolding. The 297-301 replacement mutant GA was made to understand the function of the random coil region between alpha-helices 9 and 10. Delta439-441 was constructed to decrease belt flexibility. All six mutations increased glucoamylase thermostability without significantly changing enzyme kinetic properties, with the 23-30 replacement mutation increasing the activation free energy for thermoinactivation by about 4 kJ/mol, which leads to a 4 degrees C increase in operating temperature at constant thermostability.

Aspergillus↗
PubMed2000

A dynamic focusing technique for delta-sigma-based beamformers.

Beamformation using oversampling delta-sigma (deltasigma) modulators has been proposed for diagnostic ultrasound. Such a beamformer can reduce the size, complexity and cost of an imaging system while providing adequate signal-to-quantization noise ratio (SQNR). High quality images can also be generated if dynamic receive delays are applied correctly. Several dynamic focusing techniques were previously proposed. Generally, an additional bit or extra compensation circuit is required to preserve the power and frequency distribution of the signal. Without preserving the power and frequency distribution, the image background noise is increased. In this paper, an alternative technique is presented. The new technique exploits the symmetry of focusing delays relative to the center of a transducer array. By properly synchronizing the delays and selecting the inserted values, no noise is added to the beam sum signal and the image background level is not increased. Using real ultrasound data, it is shown that the proposed technique provides the same imaging performance as the previous approaches with reduced system complexity by using only a single bit to encode the output of the deltasigma modulator.

Electronics, Medical↗
PubMed2000

Brain activation in the processing of Chinese characters and words: a functional MRI study.

Functional magnetic resonance imaging was used to identify the neural correlates of Chinese character and word reading. The Chinese stimuli were presented visually, one at a time. Subjects covertly generated a word that was semantically related to each stimulus. Three sorts of Chinese items were used: single characters having precise meanings, single characters having vague meanings, and two-character Chinese words. The results indicated that reading Chinese is characterized by extensive activity of the neural systems, with strong left lateralization of frontal (BAs 9 and 47) and temporal (BA 37) cortices and right lateralization of visual systems (BAs 17-19), parietal lobe (BA 3), and cerebellum. The location of peak activation in the left frontal regions coincided nearly completely both for vague- and precise-meaning characters as well as for two-character words, without dissociation in laterality patterns. In addition, left frontal activations were modulated by the ease of semantic retrieval. The present results constitute a challenge to the deeply ingrained belief that activations in reading single characters are right lateralized, whereas activations in reading two-character words are left lateralized.

Adult↗
PubMed2000

[The development of event related-potential acquisiting system].

A system for acquisiting event-related-potential signalsis presented, making use of random-sequences visial symbols. ATMEL AT89C51 controls Max 186 serial conversion and interface Max202 to serially send data to host computer for poct processing.

Analog-Digital Conversion↗
PubMed1999

Protein fold analysis of the B30.2-like domain.

The B30.2-like domain occurs in some members of a diverse and growing family of proteins containing zinc-binding B-box motifs, whose functions include regulation of cell growth and differentiation. The B30.2-like domain is also found in proteins without the zinc-binding motifs, such as butyrophilin (a transmembrane glycoprotein) and stonustoxin (a secreted cytolytic toxin). Currently, the function for the B30.2-like domain is not clear and the structure of a protein containing this domain has not been solved. The secondary structure prediction methods indicate that the B30.2-like domain consists of fifteen or fewer beta-strands. Fold recognition methods identified different structural topologies for the B30.2-like domains. Secondary structure prediction, deletion and lack of local sequence identity at the C-terminal region for certain members of the family, and packing of known core structures suggest that a structure containing two beta domains is the most probable of these folds. The most C-terminal sequence motif predicted to be a beta-strand in all B30.2-like domains is a potential subdomain boundary based on the sequence-structure alignments. Models of the B30.2-like domains were built based on immunoglobulin-like folds identified by the fold recognition methods to evaluate the possibility of the B30.2 domain adopting known folds and infer putative functional sites. The SPRY domain has been identified as a subdomain within the B30.2-like domain. If the B30.2-like domain is a subclass of the SPRY domain family, then this analysis would suggest that the SPRY domains are members of the immunoglobulin superfamily.

Amino Acid Sequence↗
PubMed1999

Cerebral blood flow measurement by dynamic contrast MRI using singular value decomposition with an adaptive threshold.

Singular value decomposition (SVD) is a promising deconvolution technique for use in dynamic contrast agent magnetic resonance perfusion imaging. Computer simulations, however, show that the selection of the threshold for SVD affects the accuracy of the cerebral blood flow measurements and may distort the shape of the vascular residue function. In this report, a pixel-by-pixel thresholding method is proposed based on the signal-to-noise ratio of the concentration time curve at maximum concentration (SNRC). Monte Carlo simulations were used to determine the optimal threshold for different SNRC. This technique was used to analyze data from six healthy volunteers, resulting in a mean gray to white matter cerebral blood flow ratio of 2.67 +/- 0.07. This value is in excellent agreement with values published in the literature.

Blood Flow Velocity↗
PubMed1999

Perfusion-based event-related functional MRI.

Perfusion-based event-related functional MRI was performed by measuring flow-sensitive alternating inversion recovery (FAIR) signal changes during repeated single-trial, short visual stimulation (250 msec). In the visual cortex activation area, the blood flow increases immediately after the stimulus, reaches the maximum 4 sec later with a perfusion-sensitized signal change of 16. 1 +/- 2.6 %, and then decreases to baseline approximately 11 sec after the stimuli. As it is a more direct reflection of the hemodynamic response, perfusion-based event-related functional MRI techniques may be more useful for human cognitive function studies, compared with blood oxygenation level-dependent (BOLD)-based event-related functional MRI techniques. Magn Reson Med 42:1011-1013, 1999.

Cerebrovascular Circulation↗
PubMed1999

Mutations to alter Aspergillus awamori glucoamylase selectivity. IV. Combinations of Asn20-->Cys/Ala27-->Cys, Ser30-->Pro, Gly137-->Ala, 311-4 loop, Ser411-->Ala and Ser436-->Pro.

Six previously constructed and nine newly constructed Aspergillus awamori glucoamylases with multiple mutations made by combining existing single mutations were tested for their ability to produce glucose from maltodextrins. Multiple mutations have cumulative effects on glucose yield, specific activity and thermostability. No general correlation between glucose yield and thermostability was observed, although mutations that presumably impede unfolding at high temperatures uniformly increase thermostability and generally increase glucose yield. Peak glucose yields decrease with increasing temperature. The best combination of high glucose yield, high specific activity and high thermostability occurs in Asn20-->Cys/Ala27-->Cys/Ser30-->Pro/Gly137-->Ala glucoamylase.

Aspergillus↗
PubMed1999

Expression and changes of Fos protein in the rat forebrain after gamma knife irradiation targeted to the caudate putamen.

OBJECTIVE: Forebrain expression and changes of Fos protein immunoreactivity were investigated in rats subjected to gamma knife irradiation (dose, 100 Gy), focusing on the right caudate nucleus. METHODS: Serial cryostat forebrain sections were processed with Fos protein antiserum and then by avidin-biotin-peroxidase complex immunohistochemistry after gamma knife irradiation. RESULTS: Some neurons, glial cells, and endothelial cells were positive for Fos-like immunoreactivity (LI). Fos-LI was mainly distributed in the target area of irradiation, as well as in white matter surrounding lateral ventricles, cortex, hippocampus, and certain nuclei reportedly implicated in the regulation of stress responses. From 0.5 hour to 30 days after irradiation, expression of Fos-LI displayed two peaks. The first peak arose from 3 hours to 24 hours, with cell nuclei being positive for Fos-LI. The second peak was noticeable at the 14th day postirradiation. Subsequently, three types of Fos-LI-positive cells were identified during the period between 14 and 30 days: in the first type, only the nucleus was positive; in the second type, the cytoplasm was stained; and in the third type, the cells were positive in both the nucleus and the cytoplasm. CONCLUSION: During the early stages after gamma knife irradiation, a specific stress response (significant Fos expression with two peaks) is observed not only in the target region but also in the surrounding forebrain regions. The characteristics and significance of two types of Fos-LI-positive cells are discussed in the context of this investigation.

Animals↗
PubMed1999

[Comparisons of home care utilization between insured and not-insured patients].

In the Andersen-Newman model, utilization of medical services behavior affected by the three factors of need, enabling, and predisposing. Many studies on medical services behavior adapting this model obtained the same results. Our study aimed to describe the difference of insured and non-insured patients using home care, to examine the factors that explain the long-term utilization of home care by using Andersen-Newman model, and to survey the expenditure on home care. Our study collected 486 cases by questionnaires through home interview from various home care units from Sep. 1 to Dec. 31 1994. The response rate was 68.1%. Chi-square and multiple regression tests from SAS computer program performed data analysis. Our results showed there was a significant difference in four months' utilization between insured and non-insured patients (2.38/month vs 1.72/month, p < 0.01). However, if the utilization number per month was less than two, no significance between the two groups was found. Regarding utilization behavior in home care, there were some differences among the need, enabling, and predisposing factors. Our findings demonstrated young patients, patients with chronic illness, and the Fukienese with families involving for care were willing to pay for home care despite the fact that they did not have full support from the family. The determining factors affecting long-term utilization of home care were the Fukienese, patients owning an independent house, patients with health insurance, and patients who lived in mid- or east-Taiwan. In addition, patients with an elevated number of utilizations per month and poor daily activity used home care. All dependent variables could explain 62.38% of variance. The results proposed to the authorities concerned, health institutions and medical professionals for reference in developing home care program.

Aged↗
PubMed1999

Induction of apoptosis by S-nitrosoglutathione and Cu2+ or Ni2+ ion through modulation of bax, bad, and bcl-2 proteins in human colon adenocarcinoma cells.

In this study, the amount of S-nitrosoglutathione (GSNO) was measured spectrophotometrically at 334 nm. A spontaneous decrease in absorbency at 334 nm was detected when GSNO was exposed to 37 degrees C and a high pH (pH 8.0). We investigated the catalytic roles of various metal ions on the decomposition of GSNO. The degradation of GSNO (0.5 mM) was enhanced by the presence of Cu(2+) and Ni(2+) ions. The amount of nitric oxide (NO) released from GSNO degradation was estimated by the Griess reaction based on nitrite accumulation. The results indicated that nitrite production was elevated at least twofold in the presence of Cu(2+). Our study further indicated that Cu(2+) enhanced GSNO-induced apoptosis in human colon adenocarcinoma HT 29 cells. We also found that copper ions modulated the expression of bad, bax, and bcl-2 in GSNO-treated HT 29 cells. The levels of bax and bad proteins in treated cells were significantly elevated about fourfold to sixfold when compared with mock-treated cells 24 h after combined treatment with GSNO plus Cu(2+) or Ni(2+). On the other hand, significant inhibition of bcl-2 occurred in HT 29 cells with simultaneous treatment of GSNO with Cu(2+) (or Ni(2+)). It seemed that Cu(2+) and Ni(2+) can enhance the decomposition of GSNO, which liberates NO to activate the pathways. Our results demonstrated that the apoptotic effects induced by GSNO were promoted by Ni(2+) and Cu(2+) through two different mechanisms: depletion of intracellular glutathione and triggering of NO release from GSNO, which then promotes NO-induced apoptosis in human cells.

Adenocarcinoma↗
PubMed1998

Ketoconazole-induced apoptosis through P53-dependent pathway in human colorectal and hepatocellular carcinoma cell lines.

In this study, we first demonstrated that the widely used oral antifungal drug, ketoconazole (KT), can induce apoptosis in various type of human cancer cells and in a primary culture of rat liver cells. We further investigated the molecular mechanisms of KT-induced apoptosis. It was found that KT induced nuclear accumulation of p53 protein in a dose- and time-dependent manner. The level of p53 protein was elevated approximately three times as much in treated cells 24 h after KT (5 microM) exposure as in cells receiving mock treatment. We found that cells containing wild-type p53 (COLO 205 and Hep G2) were more sensitive to KT exposure. The bax protein was induced and the bcl-2 protein was inhibited by KT in cells containing wild-type p53 (Hep G2, COLO 205) but not in cells without p53 (Hep 3B). The caspase-3 was activated 24 h after KT treatment. The Poly-(ADP ribose) polymerase (PARP) and the lamin A degradation was induced by KT, which promoted nuclear membrane disassembly and eventually caused apoptosis. Our results also indicated that none of the PKC gene family was involved in KT-induced apoptosis.

Adenocarcinoma↗
PubMed1998

Mutations to alter Aspergillus awamori glucoamylase selectivity. III. Asn20-->Cys/Ala27-->Cys, Ala27-->Pro, Ser30-->Pro, Lys108-->Arg, Lys108-->Met, Gly137-->Ala, 311-314 Loop, Tyr312-->Trp and Ser436-->Pro.

Mutations Asn20-->Cys/Ala27-->Cys (SS), Ala27-->Pro, Ser30-->Pro, Lys108-->Arg, Gly137-->Ala, Tyr312-->Trp and Ser436-->Pro in Aspergillus awamori glucoamylase, along with a mutation inserting a seven-residue loop between Tyr311 and Gly314 (311-314 Loop), were made to increase glucose yield from maltodextrin hydrolysis. No active Lys108-->Met glucoamylase was found in the supernatant after being expressed from yeast. Lys108-->Arg, 311-314 Loop and Tyr312-->Trp glucoamylases have lower activities than wild-type glucoamylase; other GAs have the same or higher activities. SS and 311-314 Loop glucoamylases give one-quarter to two-thirds the relative rates of isomaltose formation from glucose compared with glucose formation from maltodextrins at 35, 45 and 55 degrees C, correlating with up to 2% higher peak glucose yields from 30% (w/v) maltodextrin hydrolysis. Conversely, Lys108-->Arg glucoamylase has relative isomaltose formation rates three times higher and glucose yields up to 4% lower than wild-type glucoamylase. Gly137-->Ala and Tyr312-->Trp glucoamylases also give high glucose yields at higher temperatures. Mutated glucoamylases that catalyze high rates of isomaltose formation give higher glucose yields from shorter than from longer maltodextrins, opposite to normal experience with more efficient glucoamylases.

Aspergillus↗
PubMed1998

The novel estrogen-responsive B-box protein (EBBP) gene is tamoxifen-regulated in cells expressing an estrogen receptor DNA-binding domain mutant.

We have identified a 2.6-kb mRNA whose steady state levels are increased 2- to 4-fold by treatment of human mammary epithelial cells (HMEC) stably expressing an estrogen receptor (ER) transgene with either estrogen (E) or the antiestrogen, 4-hydroxy-tamoxifen (HT). The cDNA corresponding to this mRNA encodes a 564-amino acid protein, named estrogen-responsive B box protein (EBBP), that is a new member of a subfamily within the B box zinc finger protein family, which includes transcription factors (e.g. TIF1), tumor suppressor proteins (e.g. PML), and proteins implicated in development (e.g. ret finger protein, XNF7). The EBBP mRNA is detectable by Northern blot analysis in most tissues, with the exception of liver and peripheral blood lymphocytes, and the gene has been mapped to human chromosome 17p11.2. In contrast to most B box family members, EBBP has a predominantly cytoplasmic localization. Studies of the estrogenic regulation of EBBP expression demonstrated that the E-dependent increase in EBBP mRNA levels in the ER-transfected HMEC is an early, ER-mediated, and cycloheximide-insensitive process. In HMEC stably transfected with an ER mutant containing a deletion in the second zinc finger of the DNA-binding domain, E and HT had different effects on EBBP gene expression; EBBP regulation by E was dramatically reduced while the effects of HT were augmented. These data indicate that HT can modulate EBBP mRNA expression through a mutated ER, which has little activity when bound by E, and suggest that different molecular mechanisms control the E and HT responsiveness of the EBBP gene.

Amino Acid Sequence↗
PubMed1997

Infection with GB virus C and hepatitis C virus in hemodialysis patients and blood donors in Beijing.

RNAs of GB virus C (GBV-C) and hepatitis C virus (HCV) were sought by reverse-transcription polymerase chain reaction with nested primers deduced from the 5' untranslated region: 79 patients on maintenance hemodialysis, 205 commercial blood donors, and 205 voluntary donors in Beijing were studied. GBV-C RNA was detected in 43 (54%) patients and 17 (8%) commercial donors, and HCV RNA in 43 (54%) patients and 13 (6%) commercial donors, respectively. By contrast, GBV-C RNA was detected only in 2 (1%) and HCV RNA in none among 205 volunteer blood donors serving as controls. Thus both patients and commercial blood donors were at higher risk for infection with GBV-C (P < 0.001) than controls. HCV RNA was detected more often in patients with GBV-C RNA than without (29/43 or 67%, vs. 14/36 or 39%, P < 0.05) as well as in commercial donors with GBV-C RNA than without (5/17 or 29% vs. 8/188 or 4%, P < 0.01). A phylogenetic tree constructed on a sequence of 100 base pairs in the helicase region indicated that GBV-C isolates from Beijing are more similar to Japanese isolates than to isolates from the United States and Africa. Sequences from certain hemodialysis patients and those from some commercial donors were similar, suggesting nosocomial infection and spread among restricted groups.

Adult↗
PubMed1997

[Effect of 6-dimethylaminopurine on the resumption of meiosis and parthenogenetic activation in mouse oocytes].

Chromatin condensation and germinal vesicle breakdown (GVBD) in mouse cumulus free oocytes was blocked by 2 mmol/L of 6-DMAP in vitro. Mouse oocytes (M II) from superovulated female mice could be activated by 6-DMAP. The activation rates of oocytes (18-19 h post hCG) cultured in CZB medium with 2 mmol/L 6-DMAP for 0.5, 1, 2, 3 h, were 26.1%, 75.2%, 75.8%, 77.3% respectively (Table 1), and the cleavage rates of these activated oocytes were 88.2%, 73.2%, 67.0%, 58.4% respectively (Table 2). The parthenogenetic activation type induced by 6-DMAP was different from that produced by ethanol (Fig.1).

Adenine↗
PubMed1996

Effectiveness of live-attenuated Japanese encephalitis vaccine (SA14-14-2): a case-control study.

BACKGROUND: Japanese encephalitis is a major cause of death and disability throughout Asia, including the Indian subcontinent. Although an effective vaccine for Japanese encephalitis is available, hundreds of millions of susceptible individuals remain unimmunised because of the vaccine's cost. In 1988, an inexpensive live-attenuated vaccine (SA14-14-2) was licensed in China. We have measured the effectiveness of this vaccine. METHODS: In a case-control study in rural Sichuan Province, China, the 56 cases consisted of children admitted to hospital with acute Japanese encephalitis, and were confirmed serologically. 1299 village-matched and age-matched controls were identified, and vaccination histories obtained from pre-existing written records. FINDINGS: The effectiveness of one dose was 80% (95% Cl 44 to 93%); that of two doses was 97.5% (86 to 99.6%). Controlling for multiple potential confounders did not alter these results. INTERPRETATION: We conclude that a regimen of two doses of live-attenuated Japanese encephalitis vaccine, administered 1 year apart, is effective in the prevention of clinically important disease. Subsequent study is needed to assure the safety of this vaccine.

Animals↗