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H Qian

Publications and source records attributed to H Qian.

At least 19 recordsLinked to original sources
PubMed1996

Interactions between a helical residue and tertiary structures: helix propensities in small peptides and in native proteins.

We compare three complete sets of helix propensities for the 20 naturally occurring amino acids. These propensities are derived from three different experimental systems: small synthetic peptides, coiled-coil dimers, and real proteins. Thermodynamic analyses show that propensities from the different sets should be perfectly correlated if (1) the helix in a protein is formed when and only when the protein is folded (tight-coupling); and (2) the amino acid side-chains are not involved in tertiary interactions. A simple thermodynamic model is proposed in order to understand those systems that fail (1). The model incorporates fluctuations in both native and unfolded states of the protein. Measurements on hydrogen-exchange rate from proteins also question the validity of (2). A complementary model that assumes a cooperation between helix formation and tertiary structures through side-chain interactions can explain the correlation between data from the peptides and proteins. One possible source of this side-chain tertiary interaction is the amphiphilicity of helices in proteins. Our model is consistent with the ideas of "minimal frustration" and "protein malleability"; it exhibits entropy-enthalpy compensation, and suggests that local unfolding and solvent penetration are correlated in a fluctuating protein. It also suggests experiments to quantitatively verify and differentiate between the models. The electrostatic nature of hydrogen bonding and its manifestations in protein helix stability is also discussed.

Amino Acids↗
PubMed1996

Zinc enhances ionic currents induced in skate Müller (glial) cells by the inhibitory neurotransmitter GABA.

We describe here a novel effect of zinc on GABA receptors of glial cells in the skate retina. The GABA-induced currents of skate Müller cells, the radial glia of the retina, are mediated by activation of GABA(A) receptors (GABAARS). In other parts of the nervous system, GABz*-)ediated currents are inhibited by zinc. However, in isolated, voltage-clamped Müller cells, coapplication of zinc (10 microM) and GABA (1 microM) resulted in enhancement of the GABA(A)R current. Surprisingly, zinc alone induced a current similar in many respects to that elicited by GABA, i.e. the reversal potential was the same as for the GABA-induced current, the current was blocked by bicuculline and picrotoxin, and the current-voltage relation obtained in the presence of 10 microM zinc was virtually identical to that obtained with 1 microM GABA. Both bicuculline and picrotoxin suppressed a current that was present with cells bathed only in Ringer, suggesting that some of the GABA channels were spontaneously open in the absence of externally applied GABA. This possibility was supported by cell-attached patch recordings. Under conditions in which potassium and calcium currents were suppressed, spontaneous channel activity was observed. Moreover, the frequency of these channel openings was greater when zinc was included in the pipette solution, and reduced when bicuculline was added. These findings suggest that zinc acts directly to enhance the GABA(A) receptor activity of the Müller cells, and raise the possibility that the subunit composition of the GABA(A)Rs of skate Müller cells differs from that of GABA(A)Rs identified previously in other neuronal and glial preparations.

Animals↗
PubMed1996

Prediction of alpha-helices in proteins based on thermodynamic parameters from solution chemistry.

Current studies on the protein folding problem are chiefly pursued by two approaches; one statistically investigates the three-dimensional structures of proteins and the other focuses on their thermodynamic properties in solution. It remains to be demonstrated that information from these two sources are consistent and complementary. Using two sets of thermodynamic parameters experimentally obtained from solution studies, namely the helix propensities derived from small model peptides and hydrophobicity based on solvent transfer free energies for amino acids, we predict alpha-helices in native proteins. The correlation coefficient of our predictions on 98 non-homologous proteins is 0.26, a value comparable to that of the statistical prediction of Chou & Fasman but less than that from the state of the art prediction (0.39) based on neural network methodology. Helix propensities derived from different experimental systems in aqueous solutions are highly consistent for predicting alpha-helices in proteins. The helix propensities and amphiphilicity in primary sequences make independent contributions to the occurrence of alpha-helices. We also show that, with appropriate models, statistical analyses of known three-dimensional structures can provide thermodynamically relevant quantities. These findings indicate that for practical helix prediction, various sets of propensities have reached reasonable consensus. The report also suggests integrating solution thermodynamic studies with protein structural analyses, and the role of supersecondary structures on helices in proteins.

Databases, Factual↗
PubMed1996

Effects of supplemental phytase and phosphorus on histological, mechanical and chemical traits of tibia and performance of turkeys fed on soyabean-meal-based semi-purified diets high in phytate phosphorus.

Tibial traits were investigated for turkey poults fed on soyabean-meal-based semi-purified diets high in phytate P (2.2 g/kg) with added phytase and inorganic P. Dietary treatments were: (1) 2.7 g non-phytate P (nP)/kg; (2) diet 1 + 1000 U phytase/kg diet; (3) 3.6 g nP/kg; (4) diet 3 + 800 U phytase; (5) 4.5 g nP/kg; (6) diet 5 + 600 U phytase; (7) 6.0 g nP/kg. Added phytase and nP increased (P < 0.006) tibial dry matter, ash weight and content, body-weight gain, feed intake and gain:feed. The Mg and Zn concentrations in the tibial ash were also increased (P < 0.001 and P < 0.09 respectively) by added phytase or nP; tibial P and Ca concentrations tended to be increased. Hypertrophy zone width of the tibial proximal end decreased (P < 0.001), while proliferating zone width, tibial length, and widths at the long and short axes increased (P < 0.003) as phytase and nP were added. The addition of phytase also tended to enlarge the cartilaginous zone width, which was linearly increased (P < 0.05) by added nP. Disorganization scores of the hypertrophy zone and trabecular bone were low, approaching normal (P < 0.05), for turkey poults fed on diets with phytase supplementation, and tibial abnormality scores were linearly decreased (P < 0.001) as nP levels increased (zero score is considered normal). Adding phytase and nP improved the orderliness of development, mineralization and arrangement of cartilage and bone cells, and alleviated the effects of P deficiency on the histological and gross structure of the tibias. Tibial shear stress increased (P < 0.04) as phytase and nP were added. In summary, similar improvements in bone characteristics were achieved for turkey poults fed on a P-deficient diet supplemented with either phytase or nP.

6-Phytase↗
PubMed1996

Replacement of inorganic phosphorus by microbial phytase for young pigs fed on a maize-soyabean-meal diet.

Ninety-six crossbred young pigs (body weight 7.8 kg) were used in a 5-week trial to determine the effectiveness of microbial phytase (EC 3.1.3 26) in improving the bioavailabilities of P and other nutrients in maize-soyabean-meal diets and, thus, replacing inorganic P with phytase. A 2 x 5 factorial arrangement of treatments was employed with two available P (aP) levels (0.7 and 1.6 g/kg) and five phytase levels (0, 350, 700, 1050, 1400 U (the quantity of enzyme that liberates 1 mumol inorganic phosphate/min from 5.1 mm-sodium phytate at pH 5.5 and 37 degrees)/kg diet). In addition, two extra diets were formulated to supply the National Research Council (1988) recommended level of aP (3.2 g/kg) with 0 or 1400 U phytase. The addition of graded levels of phytase resulted in linear increases in average daily weight gain, average daily feed intake and weight gain:feed intake for pigs fed on diets containing 0.7 or 1.6 g aP/kg (P < 0.04). Also, the addition of phytase linearly increased apparent digestibilities of P and Ca (P < 0.01), whereas faecal P excretion was linearly decreased (P < 0.01). Linear increases in shear force, shear energy and ash content of both the metacarpal and tenth rib, and shear stress of the metacarpal were found to respond to added phytase (P < 0.01). These improvements in performance, apparent P absorption and bone measurements by phytase were also observed by increasing dietary aP levels for most measurements. Adding 1400 U phytase to the 3.2 g aP/kg diet further increased average daily weight gain, average daily feed intake, apparent absorption of P, Ca and N and metatarsal shear force and ash content (P < 0.01 to 0.05). Generally, maximum responses occurred at a phytase level of 1050 U/kg diet for the 0.7 g aP/kg diets and 700 U for the 1.6 g aP/kg diets. Based on non-linear and linear response equations generated for the phytase and aP levels, the average function of the equivalency of P (Y, g/kg) v. microbial phytase (X, U/kg) was developed across aP levels of 0.7 and 1.6 g/kg for average daily weight gain and apparent digestibility of P: Y = 2.622-2.559e 0.00185X. The replacement of 1 g inorganic P as defluorinated phosphate would require about 246 U microbial phytase. This represents 41% of released P from phytate.

6-Phytase↗
PubMed1996

Adverse effects of wide calcium:phosphorus ratios on supplemental phytase efficacy for weanling pigs fed two dietary phosphorus levels.

Ninety-six weanling pigs (initial BW = 9.3 kg, initial age = 37 d) were used in a 4-wk experiment to evaluate the response to three Ca: total (t) P ratios (1.2:1, 1.6:1, or 2.0:1) fed in combination with two P levels (.07 or .16% available that correspond to .36 or .45% tP) and two phytase levels (PY; 700 or 1,050 units/kg of diet). A 3 x 2 x 2 factorial arrangement of treatments was employed using a corn-soybean meal diet. Performance, serum mineral concentrations and alkaline phosphatase (ALP) activity, Ca and P digestibility and excretion, and bone mechanical measurements were examined. Average daily gain (P < .001), average daily feed intake (P < .01), and gain:feed (P < .05) were decreased linearly as the Ca:tP ratio became wider. The digestibility of P and Ca were decreased (P < .001) linearly as the Ca:tP ratio became wider. The digestibility of P (P < .001) and fecal P excretion (P < .01) were increased at the higher level of P. Increasing PY from 700 to 1,050 units (U)/kg of diet increased (P < .05) P digestibility and decreased (P < .01) P excretion but did not improve bone measurements. Shear force, stress and energy, and percentage of ash of both metacarpal and 10th rib linearly decreased (P < .001 to .05) as the Ca:tP ratio became wider, and bone measurements were generally greater for pigs fed the higher P level. Serum Ca concentration increased (P < .01) and the P concentration decreased (P < .001) as the Ca:tP ratio increased, but Mg, Zn, and ALP activity were not influenced by the Ca:tP ratio. Serum Ca and P concentrations were affected by PY supplementation over the 4-wk trial, but serum Mg and Zn concentrations were not affected by dietary treatments. Adverse effects of a wide Ca:tP ratio were greater at the low P diet for all responses. In addition, the activity of supplemental PY in diets seemed to be decreased as the Ca:tP ratio became wider and this negative effect of Ca:tP ratio seemed greater at the low P level, and seemed to parallel the effects of Ca:tP ratio on performance, P digestibility, bone, and serum measurements. Narrowing the dietary Ca:total P ratio from 2.0:1 to 1.2:1 led to an approximate 16% increase in phytase efficacy for improving performance, digestibility, bone measurements, and serum Ca levels.

6-Phytase↗
PubMed1996

Phosphorus equivalence of microbial phytase in turkey diets as influenced by calcium to phosphorus ratios and phosphorus levels.

Male day-old turkey poults (n = 768) were fed 0, 300, 600, or 900 U of phytase/kg of a corn-soybean diet in combination with four Ca:total P (tP) ratios of 1.1, 1.4, 1.7, and 2.0:1, and two levels of nonphytate P (nP) of 0.27 and 0.36% in a 21-d trial. Dietary Ca:tP ratios were obtained by varying defluorinated phosphate and limestone at the expense of cornstarch. The calculated dietary percentage of phytate P was 0.266 for all diets. Phytase additions linearly increased (P < 0.05) BW gain, feed intake, gain:feed, toe ash content, and apparent retentions of Ca and P at each Ca:tP ratio and nP level, but the response was influenced by dietary Ca:tP ratios and P levels. The detrimental effect (P < 0.02) of widening the Ca:tP ratio was observed for all measurements at each phytase and P level, and was greatest at lower phytase and P levels. Widening the Ca:tP ratio from 1.4 to 2.0 decreased the phytase efficacy by 7.4 and 4.9%, respectively, for 0.27 and 0.36% nP diets, which was close to the decrease in the phytase activity in vitro by 7.5 and 6.7%, respectively. The largest responses to supplemental phytase were achieved when poults were fed diets with 600 and 900 U of phytase/kg diet, respectively, for 0.36 and 0.27% nP, and for Ca:tP ratios ranging from 1.1 to 1.4:1. Second-order translog equations were generated for the phytase, Ca:tP ratio, and P effect, and nonlinear and linear equations for the phytase and Ca:tP ratio effect. Based on an assessment for the R2 and P values of equations, BW gain, feed intake, toe ash content, and P retention were sensitive measurements of the response to phytase addition. Equivalent equations were developed to determine the P equivalency of supplemental phytase. About 652 and 963 U of phytase were equivalent to 1 g nP, respectively, for 0.27 and 0.36% nP diets in turkey poults from hatch to 21 d of age.

6-Phytase↗
PubMed1996

Effects of supplemental phytase and phosphorus on histological and other tibial bone characteristics and performances of broilers fed semi-purified diets.

Two trials with day-old chicks were conducted to investigate the effects of supplemental phytase (Natuphos) on histological, mechanical, and chemical properties of tibia, and performances of broilers fed semi-purified diets containing soybean meal as the only organic P source [0.11% nonphytate P (nP)]. Dietary treatments in Trial 1 were: 1) 0.20% nP, 2) Diet 1 + 800 U of phytase/kg of diet, 3) 0.27% nP, 4) Diet 3 + 600 U of phytase, 5) 0.34% nP, 6) Diet 5 + 400 U of phytase. Supplemental phytase and inorganic P increased tibial length (P < 0.01), shear force (P < 0.001), shear stress (P < 0.05), ash content (P < 0.001), and BW gain and feed intake (P < 0.001) during Trial 1. The hypertrophic zone width at the proximal end of the tibia was decreased (P < 0.05), and the tibial width (P < 0.05) of the long axis of the tibia was increased by the phytase and P supplementation. Supplemental phytase enlarged the cartilaginous and proliferative zones of the tibial proximal end (P < 0.05), and an increase in nP levels produced similar effects. Supplementation of phytase and P also tended to improve the orderliness of development and arrangement of cartilage and bone cells. Dietary treatments in Trial 2 were: 1) 0.27% nP, 2) Diet 1 + 350 U of phytase, 3) Diet 1 + 1,050 U of phytase, 4) 0.45% nP, 5) 0.54% nP, 6) Diet 5 + 1,050 U of phytase. Broilers fed diets containing relatively high levels of nP and phytase supplementation in Trial 2 gave results similar to those observed in Trial 1. Marked improvements (P < 0.05) in the ash content, shear force, shear stress, length of tibia, BW gain, and feed intake, and reduced hypertrophic zone width were achieved for broilers fed the P-deficient diet supplemented with phytase. Also, supplemental phytase tended to increase the width of cartilaginous and proliferative zones, to increase trabecular bone density, and to improve the orderliness of development and mineralization of cartilage and bone cells. In summary, supplementing a low-nP diet with inorganic P or phytase resulted in similar beneficial effects on bone development.

6-Phytase↗
PubMed1995

GABAA and GABAC receptors on hybrid bass retinal bipolar cells.

1. gamma-Aminobutyric acid (GABA) responses from solitory hybrid bass retinal bipolar cells were studied with the use of conventional and perforated whole cell patch-clamp recording. 2. GABA elicited a chloride current in bipolar cells that had both transient and sustained components. The transient component was sensitive to bicuculline and resembled GABAA-mediated currents, whereas the more sustained component was resistant to bicuculline and resembled the responses mediated by GABAC receptors. 3. The bicuculline-resistant GABA responses recorded from the bipolar cells could not be modulated by either diazepam or pentobarbital sodium, and they were unaffected by phaclofen and 2-hydroxysaclofen, GABAB receptor antagonists. On the other hand, the bicuculline-resistant GABA responses could be blocked substantially by imidazole-4-acetic acid (I4AA), a competitive antagonist of GABAC receptors. 4. Noise analysis of the GABA-elicited currents suggested a different single channel conductance for GABAA (10.1 pS) and GABAC receptors (3.6 pS). 5. Zinc, a putative modulator of synaptic transmission, strongly inhibited the GABAC responses on bipolar cells, whereas the GABAA responses were not significantly affected by zinc. 6. The proportion of the GABAC to GABAA responses varied widely between bipolar cells. Local application of GABA onto dendrites or axon terminals showed that both types of GABA receptors are present on both regions of the cell. 7. The distinct properties of these two GABA receptor types suggest that they play different roles in retinal function.

Animals↗
PubMed1995

[Clinical analysis of 6 cases of gestational trophoblastic neoplasms complicated by cardiotoxicity after chemotherapies].

Gestational trophoblastic neoplasm treated by large dosage of 5-fluorouracil and actinomycin could cause cardiotoxicity. In 6 cases of gestational trophoblastic neoplasms admitted to our hospital from March to December 1993, cardiotoxicity was found to have occurred after chemotherapies in 10/21 courses. There were 2 cases with heart failures, 4 cases with palpitation and 4 cases with feelings of oppression and (or) chest pains. In 7 cases the electrocardiogram (EKG) findings were abnormal (70.0%) and in 5 cases there were increased sera glutamic oxalacetic transaminase enzyme (AST). 90.0% of these complications were brought under control after decreasing the dosages and changing the methods of administration. If the proper managements were not given on time, patient may even expire. So attention should be paid to this complication. It is suggested that attention should be paid to patients' subjective symptoms, and proper surveillance by EKG and serum AST determinations should be conducted to minimize deaths due to chemotherapeutic complications.

Adult↗
PubMed1995

[Influence of radioimmunoimaging on the survival rate of ovarian carcinoma patients].

Two groups of patients suffered from ovarian carcinoma were studied retrospectively after similar treatments; in one group of 22 patients radioimmunoimaging (RII) had been used, which was not used in the other group of 15 patients. Other factors were similar in the two group such as hospitalization period, courses of surgical treatment and regimes of chemotherapy after surgery. The staging according to FIGO was also similar in the two groups except that the number of patients in stage III was 14 in the RII group but 8 in the non-RII group. Neither the age distribution nor the histopathological diagnosis was of much difference. 131I labeled monoclonal antibody against ovarian serous adenocarcinoma, generated in our laboratory, was given to all patients intraperitoneally either before or after the surgery; 7 cases before the initial operation, 9 cases before the second look operation and 6 cases for follow up after surgery and chemotherapy. The death rates of stage III were 42.9% and 75.0% in the RII group and non-RII group respectively. By means of Kaplain Meir's life table calculation the 3 year survival rates for the two groups were 63.5% and 25.0% respectively. The RII group was obviously higher than the non-RII group even though not statistically significant. These results were similar to those reported in the literature. Three very late cases of ovarian carcinoma were reported, in whom RII had been used, are still living after follow-up for more than 5 years. The beneficial role of induction of the idiotypic network was discussed, and the possibility of innoculation is under investigation.

Antibodies, Monoclonal↗
PubMed1995

[Current malaria stratification in China].

During the past 30 years since 1958 when malaria stratification was first made, a great change in malaria situation has occurred. The original stratification can not represent the current status of malaria distribution. Therefore, it needs to be redivided so as to provide basis for future malaria control work. Taking species of mosquito vector and malaria incidence as the main indices and making reference to the natural geographical division, the current malaria endemic area in China can be divided into four regions, i.e. (1) Western region: it is mostly a natural non-endemic area, except some limited areas with sporadic cases in Xinjiang Autonomous Region; (2) Northern region: the whole north-eastern and partial northern China belong to the areas where malaria has been basically eliminated; but sporadic occurrence still exist in most part of the northern China; (3) Central region: it is mostly a hypo-endemic area, only a small part has meso-endemicity; (4) Southern region: nearly 50% has meso-endemicity and the other 50% has hypo-endemicity. The demarcation line of natural non-endemic areas and the areas where malaria has been basically eliminated has been defined.

Animals↗
PubMed1995

[The analysis of tumor growth rate and histopathology of xenografts of nude mice bearing human ovarian carcinoma in immunocompetent mice].

Xenografts of nude mice bearing human ovarian carcinoma cell line SKOV3 were transplanted using subrenal capsule assay (SRCA) in immunocompetent C57BL/6 mice. Multiple locations were chosen on both sides of the kidneys obtaining a total of 129 tumors. The volumes of the tumors were measured and histopathological examinations were conducted on the 4th, 6th, 8th, 10th, 12th and 14th days after transplantation surgery. The growth rates were noticed to be high on the 6-8th days. Lymphocytic infiltration reached a peak on the 8-12th day. On the 14th days the leukocytic infiltration and fibrosis almost surrounded the tumors. Tumor cells that could be found amounted to about 77.25%, 65.38%, and 52.17% respectively on the 4th, 6th and 8th days, but significantly decreased on 12-14th days. The above results suggested: (1) multiple SRCA on both sides proved to be practical and economical; (2) the xenografts of nude mice bearing hman ovarian carcinoma could be transplanted viably by SRCA for 8-10 days; (3) microscopic measurements of the transplanted tumor volume did not represent the real status of the tumor growth, and microscopic evaluation was necessary.

Animals↗
PubMed1995

[The significance of p53 gene mutations and expressions in human colorectal tumors].

Using a polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) approach we analyzed 18 human colorectal adenocarcinomas for mutations in exons 5, 6, 7, 8 of p53 gene. At the same time, p53 gene product expression was studied immunohistochemically in these 18 cases in frozen sections. The expression of p53 protein was also immunohistochemically studied in formalin-fixed paraffin embedded specimens of 76 colorectal adenocarcinomas and 112 colorectal polyps. Eight out of 18 cases (44%) tested showed a variant band indicative of a mutation in exons 5-6 of p53 gene. Seven out of 8 cases (88%) with p53 gene mutations were positively stained for p53. There was no significant correlation between p53 expression and clinicopathological manifestations and prognosis. But the strongest staining was encountered in those cases with well differentiated and early stages of adenocarcinomas, while weaker staining was encountered in poorly differentiated and mucoid adenocarcinomas. p53 expression was not observed in proliferative polyps and adenomas with low grade dysplasia. The frequency of p53 expression reached 88% (P < 0.001) when adenoma showed malignant change. Among three types of adenomas, p53 expression was most frequent in villous type (P < 0.05). The frequency of p53 expression in adenoma, adenoma with malignant change and adenocarcinoma was 4%, 88% and 51% respectively. These indicate that genetic changes of p53 gene play an important role in the transformation from benign adenoma to adenocarcinoma. p53 immunohistochemistry can be used as a surrogate marker for p53 gene mutation for early discovery of colorectal adenocarcinomas.

Adenocarcinoma↗
PubMed1994

A thermodynamic model for the helix-coil transition coupled to dimerization of short coiled-coil peptides.

A simple thermodynamic formalism is presented to model the conformational transition between a random-coil monomeric peptide and a coiled-coil helical dimer. The coiled-coil helical dimer is the structure of a class of proteins also called leucine zipper, which has been studied intensively in recent years. Our model, which is appropriate particularly for short peptides, is an alternative to the theory developed by Skolnick and Holtzer. Using the present formalism, we discuss the multi-equilibriatory nature of this transition and provide an explanation for the apparent two-state behavior of coiled-coil formation when the helix-coil transition is coupled to dimerization. It is found that such coupling between multi-equilibria and a true two-state transition can simplify the data analysis, but care must be taken in using the overall association constant to determine helix propensities (w) of single residues. Successful use of the two-state model does not imply that the helix-coil transition is all-or-none. The all-or-none assumption can provide good numerical estimates when w is around unity (0.35 < or = w < or = 1.35), but when w is small (w < 0.01), similar estimations can lead to large errors. The theory of the helix-coil transition in denaturation experiments is also discussed.

Macromolecular Substances↗
PubMed1994

A novel action of quinine and quinidine on the membrane conductance of neurons from the vertebrate retina.

The cinchona alkaloids quinine and quinidine have been shown to block a broad range of voltage-gated membrane conductances in a variety of excitable tissues. Using the whole-cell version of the patch clamp technique, we examined the effects of these compounds on voltage-dependent currents from horizontal cells dissociated enzymatically from the all-rod retina of the skate. We report here a novel and unexpected action of quinine and quinidine on isolated horizontal cells. In addition to blocking several of the voltage-activated currents of these cells, the introduction of the alkaloids evoked a large outward current when the cells were held at depolarized potentials. Using tail current analysis, the reversal potential of the outward current was close to O mV, and the current was markedly suppressed by extracellularly applied cobalt, acetate, and halothane. Depolarization in the presence of quinine also permitted entry into the cells of extracellularly applied Lucifer yellow (MW = 443 D), whereas a 3-kD fluorescein-dextran complex was excluded. These findings suggest that the large, apparently nonselective conductance induced by quinine and quinidine results from the opening of hemi-gap junctional channels.

Animals↗