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Biomedical subjects

D Zhang

Publications and source records attributed to D Zhang.

At least 613 records · Page 34Linked to original sources
PubMed1993

(S)-geranylgeranylglyceryl phosphate synthase. Purification and characterization of the first pathway-specific enzyme in archaebacterial membrane lipid biosynthesis.

The first pathway-specific step in the biosynthesis of the core membrane diether lipids in archaebacteria is the alkylation of the primary hydroxyl group in (S)-glyceryl phosphate by geranylgeranyl diphosphate. The reaction is catalyzed by (S)-3-O-geranylgeranylglyceryl phosphate ((S)-GGGP) synthase. The cytosolic enzyme was purified to homogeneity from the moderately thermophilic archaebacterium Methanobacterium thermoautotrophicum by a combination of ammonium sulfate precipitation, four chromatographic steps (DE52, Q-Sepharose, phenyl-Superose, and Protein Pak), and native polyacrylamide gel electrophoresis. SDS-polyacrylamide gel electrophoresis of gel-purified GGGP synthase gave a single band at 29 kDa. The enzyme requires Mg2+ for optimal activity, although prenyltransfer is also seen in buffers containing Mn2+ or Zn2+. A well defined pH optimum occurs between 6.0 and 7.5. Maximal activity is seen at 50-65 degrees C. The Michaelis constants for GGGP synthase are Vmax = 4.1 +/- 0.5 mumol min-1 mg-1, KMGGPP = 4.1 +/- 1.1 microM, and KMGP = 41 +/- 5 microM.

Alkyl and Aryl Transferases↗
PubMed1993

Calsequestrinlike calcium-binding protein is expressed in calcium-accumulating cells of Pistia stratiotes.

To contend with high calcium (Ca) levels in the environment, many plant species contain crystal idioblasts, specialized cells which accumulate large amounts of Ca as oxalate crystals. The biochemical processes involved in the accumulation of Ca in crystal idioblasts are unknown, as these cells constitute only a minor proportion of the total plant tissue. To address how crystal idioblasts buffer cytosolic Ca during crystal formation, we purified these cells from water lettuce and assessed their biochemistry. We show here that crystal idioblast cells contain three Ca-binding proteins not detectable in mesophyll cells. One of the Ca-binding proteins shares antigenicity with rabbit calsequestrin, a high-capacity low-affinity Ca-binding protein, and is encoded by related nucleotide sequences. Immunocytochemical localization studies further demonstrate that a calsequestrinlike protein is present primarily in crystal idioblasts and is preferentially localized in the endoplasmic reticulum, an organelle enriched in Ca as evidenced by vital staining. We thus conclude that crystal idioblasts possess a buffering system involving calsequestrinlike proteins, a process that likely plays an essential role in the bulk control of Ca in plant cells.

Calcium↗
PubMed1993

31P relaxation rates to evaluate physiological events in the heart.

The present study was performed to determine whether 31P NMR relaxation times (T1) of adenosine triphosphate (ATP) might be used to monitor the resultant altered myocardial physiology produced by ischemia and possibly to explain mechanisms of altered physiology. To this end, pre- and postischemic T1s were determined in hearts perfused in the Langendorff mode, using 31P NMR inversion recovery methods. In hearts without any pretreatment (CON), post-ischemic ATP T1 values were significantly decreased compared with pre-ischemic values (P < 0.05); Pre-isch: gamma = 0.58 +/- 0.08; alpha = 0.62 +/- 0.06; beta = 0.38 +/- 0.08; Post-isch: gamma = 0.33 +/- 0.05; alpha = 0.43 +/- 0.03; beta = 0.23 +/- 0.05. In groups pretreated with creatine (CR), cyclocreatine (CY), or superoxide dismutase plus catalase (SOD-CAT) before ischemia, the post-ischemic ATP T1 values were similar and were not significantly changed from pre-ischemic values. These combined data suggest that T1s of ATP might be used to monitor altered myocardial physiology and could provide insight into mechanisms of alteration.

Adenosine Triphosphate↗
PubMed1993

Yeast squalene synthase: expression, purification, and characterization of soluble recombinant enzyme.

Squalene synthase is the first pathway-specific enzyme in the cholesterol biosynthetic pathway. The gene (ERG9) encoding squalene synthase in Saccharomyces cerevisiae has been isolated and characterized (S. M. Jennings, Y. H. Tsay, T. M. Fisch, and G. W. Robinson, 1991, Proc. Natl. Acad. Sci. USA 88, 6038-6042: M. Fegueur, L. Richard, A. D. Charles, F. Karst, 1991, Curr. Genet. 20, 365-372). The structural gene for the enzyme was modified by the polymerase chain reaction to remove a hydrophobic C-terminal domain, and the open reading frame for the truncated protein was cloned into yeast and Escherichia coli expression vectors. In E. coli, overexpressed truncated squalene synthase was soluble and constituted 2-5% of total cellular protein. The recombinant enzyme was purified to > 95% homogeneity in two steps by chromatography on hydroxyapatite and phenyl-Superose. Soluble truncated squalene synthase is monomeric and catalyzes the two-step conversion of farnesyl diphosphate (FPP) to squalene via presqualene diphosphate in the presence of Mg2+ and NADPH. The concentration of FPP needed for half-maximal activity was 40 microM. At higher concentrations, FPP was an inhibitor. The activity of squalene synthase was stimulated by detergents and reached a maximal value of kcat = 3.3 s-1 at 100 microM FPP in the presence of 1% (v/v) Tween 80.

Base Sequence↗
PubMed1993

Analysis and purification of phosphorylated isoprenoids by reversed-phase HPLC.

Procedures were developed for analysis and purification of phosphorylated isoprenoids by reversed-phase HPLC. Dimethylallyl diphosphate (C5), geranyl diphosphate (C10), farnesyl diphosphate (C15), geranylgeranyl diphosphate (C20), and farnesylgeranyl diphosphate (C25) were cleanly separated on a C18 column by gradient elution with acetonitrile and 25 mM NH4HCO3. Reversed-phase HPLC was used to directly analyze extracts for phosphorylated isoprenoids and to follow the progress of enzyme-catalyzed reactions without having to hydrolyze the phosphate esters before analysis. Examples are provided for geranylgeranyl diphosphate synthase, geranylgeranylglyceryl phosphate synthase, and squalene synthase. The separations were run on preparative scales to purify products from the enzymatic reactions for mass spectrometry and to purify synthetic substrates.

Bicarbonates↗
PubMed1993

Assignment of the three disulfide bridges of huwentoxin-I, a neurotoxin from the spider selenocosmia huwena.

The positions of the disulfide bonds of huwentoxin-I, a neurotoxin from the spider Selenocosmia huwena, have been determined. The existence of three disulfide bonds in the native toxin was demonstrated by mass spectroscopy and the lack of reactivity with a thiol reagent. The assignment procedure involved a combination of tryptic digestion of the native toxin and sequence analysis of both intact and in situ S-carboxymethylated toxin. In situ carboxymethylation is shown to be a useful procedure in sequencing of cysteine- and cystine-containing peptides. Sequence analysis of the intact, cross-linked toxin indicated that no amino acid phenylthiohydantoin (PTH) derivative is seen for the first half-cystine in a cross-linked pair, but that the PTH of dehydroalanine, which can be detected at 313 nm, is seen at the position of the second half-cystine. By sequencing disulfide cross-linked tryptic fragments, the three disulfide linkages in huwentoxin-I could be assigned as Cys2-Cys17, Cys9-Cys22, and Cys16-Cys29.

Amino Acid Sequence↗
PubMed1993

Gynecologic complications of cyclic estrogen progestin therapy.

We evaluated the long-term gynecologic risks of postmenopausal estrogen therapy in conjunction with cyclic, monthly progestin (progestin-estrogen replacement therapy, or PERT). Our medical record review showed that incidence of abnormal vaginal bleeding necessitating gynecologic procedures for evaluation was significantly higher (RR, 3.1; 95% CI, 2.1-4.5), as was the rate of endometrial biopsy (RR, 3.4; 95% CI, 2.3-5.1), among women receiving PERT than among women not receiving hormone therapy. We also identified a non-significant trend toward a higher rate of dilation and curettage (RR, 1.5; CI, 0.7-3.3) among women receiving PERT. However, rates of endometrial hyperplasia and hysterectomy were similarly low in both groups. PERT apparently protects women against these serious gynecologic consequences previously seen in women taking unopposed estrogen.

Biopsy↗
PubMed1993

H-2z homozygous New Zealand mice as a model for B-cell chronic lymphocytic leukemia: elevated bcl-2 expression in CD5 B cells at premalignant and malignant stages.

In New Zealand mice, the major histocompatibility complex (MHC) controls the development of both autoimmune disease and B cell chronic lymphocytic leukemia (B-CLL). While H-2d/H-2z heterozygosity acts as one major predisposing genetic element for autoimmune disease, H-2z/H-2z homozygosity acts as an element for B-CLL. In the H-2z/H-2z homozygotes, there was an age-dependent increase in frequencies of CD5 B cells in the blood and spleen, and such CD5 B cells showed oligoclonal to monoclonal expansion, giving rise to B-CLL. B-CLL cells from these mice had surface phenotypes typical of CD5 B lineage cells, and expressed high levels of proto-oncogene bcl-2. Elevated bcl-2 expression was also observed in premalignant B cells in the aged mice, thereby suggesting that apoptosis-resistant, long-surviving CD5 B cells with a self-renewal capacity form the basis of malignant transformation. This model not only provides clues for analyzing multiple steps of genetic alterations involved in the generation of B-CLL, but also sheds light on the correlation between B-CLL and autoimmune disease.

Animals↗
PubMed1993

Effect of temperature and coronary flow on the metabolic and mechanical function of the isolated rat heart.

A number of cardiac metabolic intermediates, namely, adenosine triphosphate (ATP), H+, phosphocreatine (PCr), inorganic phosphate (Pi), adenosine diphosphate (ADP), and related functions of these intermediates, Gibbs' free energy of ATP hydrolysis (delta G) and phosphorylation ratio [ATP/(ADP.Pi)], are thought to adjust mitochondrial oxidative phosphorylation rates to conform to mechanical demand. The effects of hypothermia and altered perfusion pressure on these parameters were evaluated in 12 hearts from Sprague-Dawley rats perfused in the Langendorff mode. 31P-nuclear magnetic resonance (NMR) spectra were obtained at cardiac temperatures between 20 and 37 degrees C, and coronary perfusion pressures between 20 and 145 cm H2O. Coronary flow varied between 0.5 and 15 ml/min throughout this range of intervention. Heart rate (HR), left ventricular systolic pressure (LVSP), and specific volumetric coronary flow (SCF) were determined for each temperature and perfusion pressure. The product HR x LVSP directly correlated with perfusion pressure at all temperatures. The temperature dependence could be represented by an overall activation energy of 72.7 kJ/M. In the constant temperature experiment, SCF and HR x LVSP fell linearly with decreasing perfusion pressure. Quantitative evaluation of the relationship between cardiac function and the metabolic intermediates described above defined these intermediates as nonregulatory with the possible exception of H+.

Acid-Base Equilibrium↗
PubMed1993

LDL subclass phenotypes and the insulin resistance syndrome in women.

BACKGROUND: Low-density lipoprotein (LDL) subclass phenotype B, characterized by predominance of small, dense LDL particles, is associated with elevated plasma triglycerides and apolipoprotein B and with lower high-density lipoprotein (HDL) cholesterol and apolipoprotein A-I. Because these abnormalities resemble the dyslipidemia of insulin resistance, we examined associations of LDL subclass phenotype with plasma insulin levels and with other aspects of the insulin resistance syndrome. METHODS AND RESULTS: LDL subclass phenotypes were determined by gradient gel electrophoresis in 682 female twins aged 30 to 91 years who participated in the second examination of the Kaiser Permanente Women Twins Study. Prevalence of phenotype B and the intermediate phenotype (I) increased strongly with age, obesity, and non-insulin-dependent diabetes. In multivariate analysis of nondiabetic women, phenotype B or I was independently associated with each aspect of the insulin resistance syndrome, including higher plasma triglycerides, waist-hip ratio, fasting and postload insulin levels, and systolic blood pressure and lower HDL cholesterol levels after adjustment for age and body mass index. The prevalence of phenotype B or I rose progressively from 5.6% in women with no manifestations of the insulin resistance syndrome to 100% in women with four syndrome components. In 25 nondiabetic, monozygotic twin pairs discordant for subclass phenotype, the twins with phenotype B (or I) had significantly higher levels of body mass index, waist-hip ratio, and systolic blood pressure than their twins with phenotype A. Thus, nongenetic variation in these risk factors is important in explaining their associations with LDL subclass phenotype. CONCLUSIONS: Small, dense LDL is an integral feature of the insulin resistance syndrome. Nongenetic (ie, behavioral or environmental) factors are important for the expression of the phenotype and for its association with other heart disease risk factors.

Adult↗
PubMed1993

Research note: responses of laying hens on saline drinking water to dietary supplementation with various zinc compounds.

Production variables, eggshell defects, eggshell quality, the concentration of calcium-binding protein (CaBP), and the activity of carbonic anhydrase (CA) in the shell gland mucosa were determined in hens receiving town water (10 mg Na/L), or town water supplemented with 2 g NaCl/L (796 mg Na/L). Five treatments were examined. Control hens received town water and a proprietary layer mash containing .17% Na. The remaining four treatments received the water containing NaCl (2 g/L). Hens of Treatment 2 were fed the proprietary layer mash and those of Treatments 3, 4, and 5 received, respectively, the layer mash containing supplements of Zn-methionine (Zinpro-200; .5 g/kg), Zn sulfate (ZnSO4.7H2O; .46 g/kg), or chelated Zn-EDTA (.54 g/kg) to supply the same concentration of Zn (.1 g/kg). The treatments were applied for 6 wk. Hens receiving the saline drinking water without any dietary Zn supplement produced significantly (P < .05) more eggs with shell defects than hens receiving the town water. This increase in the incidence of eggshell defects was associated with significant reductions in eggshell breaking strength, the concentration of CaBP, and the activity of CA. Supplementing the saline drinking water with any of the three Zn compounds significantly reduced the incidence of eggshell defects and in some cases improved shell breaking strength, the concentration of CaBP, and the activity of CA.

Animal Feed↗
PubMed1993

[Observation on the phenomenon of propagated sensation along meridians in youngsters].

That the opinion on the relation between the propagated sensation along meridians (PSM) and the age of the subjects was divergent in the results reported by some authors. In the last 10 years, we have performed a systematic investigation on PSM on a group of 536 youngsters. The main characteristics of PSM in youngsters were just the same as that of adults. However, the incidence of PSM in youngsters, particularly the degree of distinctness of PSM, was by far higher than that of adults. The results were stable and could be repeated in the experiments performed in different years. It showed that there was surely a close relation between the degree of distinctness of PSM and the age of subjects. This fact can not be appropriately explained at present. However, it provides an important clue to clarify the factors which influence the appearance of PSM, and in turn to promote the improvement of the therapeutic effect of acupuncture and cilacriation of the mechanism underlying the formation of PSM.

Acupuncture Therapy↗
PubMed1993

[Evaluation of pulmonary arterial pressure by pulsed Doppler echocardiography compared with cardiac catheterization].

Twenty-six patients undergoing right cardiac catheterization were examined by pulsed doppler echocardiography (PDE), spectrum analysis of the shape of flow velocity curve of the pulmonary arteria during systole was made. Pulmonary arterial pressure (PAP) was qualitatively and qualitatively evaluated by right ventricular systolic time interval (RSTI) derived from pulmonary doppler blood flow velocity pattern. The correlation between PAP and the values of RSTI was evaluated, multiple stepwise regression analysis was performed. The pulmonary flow pattern and the values of RSTI measured from right ventricular outflow tract (RVOT) and main pulmonary artery (MPA) were compared. The results showed that: 1. Qualitative evaluation of PAP: (1) the triangular configuration of the pulmonary flow pattern was the feature of the pulmonary ejection flow in pulmonary hypertension (PH). (2) AT < 100ms AT/ET < 0.30 and PEP/AT > 1.1 indicated PH (PAMP > or = 2.7 kPa, AT < 100 ms, sensitivity 92.3%, specificity 100%). 2. Quantitative evaluation of PAP: (1) simple regression analysis: AT, AT/PEP especially AT showed a good inverse correlation with PAP, which was improved when a logarithmic function was applied, but not improved by the square root of heart rate. The liner regression equation and the correlation coefficient were: log PASP = -6.3617 AT +2.825 (r = -0.7925, P < 0.001); log PADP = -0.4569 AT +74.182 (r = -0.8513, P < 0.001); log PAMP = -0.0073 AT +2.198 (r = -0.8635, P < 0.001). (2) multiple stepwise regression analysis: the stepwise analysis of six parameters (PEP, ET, AT, AT/ET, AT/PEP, square root of R-R) showed that AT, PEP were the best parameters correlated with PAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Clinical and experimental studies of JPYS in reducing side-effects of chemotherapy in late-stage gastric cancer.

This article reports a research project undertaken for more than 16 years by the Cancer Department of Guang An Men Hospital. Tonic Jian Pi Yi Shen (JPYS), which nourishes the spleen and kidney, was used in combination with chemotherapy in the treatment of late stage gastric cancer patients for the purpose of promoting completion of the chemotherapeutic course, improving the general condition, ameliorating the reaction in the digestive system, protecting hemopoiesis and strengthening immunocompetence. The results of lab experiments were found to coincide with those of clinical application.

Adenocarcinoma↗
PubMed1992

Blockade of NMDA receptor-mediated mobilization of intracellular Ca2+ prevents neurotoxicity.

NMDA receptor activation leads to elevated Ca2+ in cultured rat cortical and retinal ganglion cell neurons. If excessive, this Ca2+ response is associated with delayed neurotoxicity. We used dantrolene and ionomycin to test if the Ca2+ response to NMDA was due to mobilization of intracellular Ca2+ stores rather than merely to Ca2+ influx. In the presence of EGTA, ionomycin resulted in release and subsequent depletion of intracellular Ca2+ stores. Henceforth, despite normal extracellular Ca2+, NMDA elicited only about half of its former Ca2+ response. Similarly, when dantrolene was used to block Ca2+ release from intracellular stores, we observed > 50% smaller NMDA-evoked Ca2+ responses. These results quite surprisingly indicate that at least half the Ca2+ response to NMDA is due to release of intracellular Ca2+, a process triggered by influx of extracellular Ca2+. Dantrolene also protected neurons from NMDA receptor-mediated neurotoxicity. Release of intracellular Ca2+ may therefore be a necessary step in the cascade leading to neuronal damage induced by excessive NMDA receptor stimulation and may be amenable to pharmacological intervention.

Animals↗
PubMed1992

Colocalization of enkephalin-, glucagon-, and corticotropin-releasing factor-like immunoreactivity in GABAergic amacrine cells in turtle retina.

The large number of amacrine cells which contain gamma-aminobutyric acid (GABA) in the turtle retina makes it difficult to examine specific GABAergic cell types. In order to selectively label subpopulations of GABAergic neurons, we have used fluorescent double-labeling immunocytochemical techniques to examine the localization of GABA-like immunoreactivity (LI) in amacrine cells which contain antigens resembling the neuropeptides glucagon (GLUC), corticotropin-releasing factor (CRF) or enkephalin (ENK). GABA-LI was found in 41% of the cells with GLUC-, 100% of the cells with CRF-, and 69% of the cells with ENK-LI. There were regional differences in the presence of GABA-LI in amacrine cell populations with ENK-LI. GABA-LI was present in about 80% of the cells with ENK-LI outside of the visual streak, while only 37% of the cells within the streak had GABA-LI. Based on the distinct morphologies and regional distributions of these peptidergic amacrine cells, we conclude that they represent different subpopulations of GABAergic amacrine cells in the turtle retina. Future studies can now utilize existing information regarding the synaptic connectivity of these peptidergic amacrine cells to help delineate the functions of GABAergic amacrine cells in the turtle retina.

Animals↗
PubMed1992

Glutamate-immunoreactive terminals synapse on primate spinothalamic tract cells.

Glutamate has been shown to excite spinothalamic tract (STT) neurons and has been localized to primary afferent neurons, spinal cord projection neurons, and interneurons in the spinal cord dorsal horn. The likelihood that glutamate-immunoreactive (GLU-IR) terminals directly innervate STT neurons was investigated. For these studies three lamina IV or V STT cells in the lumbar spinal cords of three monkeys (Macaca fascicularis) were identified electrophysiologically and characterized. Two were identified as high threshold neurons and one as a wide dynamic range neuron. Following intracellular injection of the cells with HRP and reaction to give the cells a Golgi-like appearance, the tissues were processed for electron microscopy. Postembedding immunogold methods with antibodies specific for glutamate were used to identify GLU-IR terminals apposing the somata and dendrites of the STT neurons, including dendrites that extended into laminae IV and III. The GLU-IR terminals were numerous and constituted a mean of 46% of the population counted that appose the STT soma and 50% of the profiles apposing the dendrites. Fifty-four percent of the somatic and 50% of the dendritic surface length was contacted by GLU-IR terminals. Most terminals contained round clear vesicles and some contained a variable number of large dense core vesicles. For one of the three cells examined it was determined that 45% of the terminals apposing the soma were GLU-IR and 30% of the terminals were gamma aminobutyric acid-immunoreactive (GABA-IR). In an additional monkey, a lamina I cell retrogradely labeled from the ventral posterolateral nucleus of the thalamus was found to be ensheathed in glial processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗