Biomedical subjects
Publications and source records attributed to Z Xu.
A recursion formula of energy levels for Oxygen-like ions has been given based on the generalization of the perturbation expansion. It is found that the formula is considerably simple and accurate.
The terbenzimidazoles are a class of synthetic ligands that poison the human topoisomerase I (TOP1) enzyme and promote cancer cell death. It has been proposed that drugs of this class act as TOP1 poisons by binding to the minor groove of the DNA substrate of TOP1 and altering its structure in a manner that results in enzyme-mediated DNA cleavage. To test this hypothesis, we characterize and compare the binding properties of a 5-phenylterbenzimidazole derivative (5PTB) to the d(GA4T4C)2 and d(GT4A4C)2 duplexes. The d(GA4T4C)2 duplex contains an uninterrupted 8-bp A.T domain, which, on the basis of x-ray crystallographic data, should induce a highly hydrated "A-tract" conformation. This duplex also exhibits anomalously slow migration in a polyacrylamide gel, a feature characteristic of a noncanonical global conformational state frequently described as "bent." By contrast, the d(GT4A4C)2 duplex contains two 4-bp A.T tracts separated by a TpA dinucleotide step, which should induce a less hydrated "B-like" conformation. This duplex also migrates normally in a polyacrylamide gel, a feature further characteristic of a global, canonical B-form duplex. Our data reveal that, at 20 degrees C, 5PTB exhibits an approximately 2. 3 kcal/mol greater affinity for the d(GA4T4C)2 duplex than for the d(GT4A4C)2 duplex. Significantly, we find this sequence/conformational binding specificity of 5PTB to be entropic in origin, an observation consistent with a greater degree of drug binding-induced dehydration of the more solvated d(GA4T4C)2 duplex. By contrast with the differential duplex affinity exhibited by 5PTB, netropsin and 4',6-diamidino-2-phenylindole (DAPI), two AT-specific minor groove binding ligands that are inactive as human TOP1 poisons, bind to both duplexes with similar affinities. The electrophoretic behaviors of the ligand-free and ligand-bound duplexes are consistent with 5PTB-induced bending and/or unwinding of both duplexes, which, for the d(GA4T4C)2 duplex, is synergistic with the endogenous sequence-directed electrophoretic properties of the ligand-free duplex state. By contrast, the binding to either duplex of netropsin or DAPI induces little or no change in the electrophoretic mobilities of the duplexes. Our results demonstrate that the TOP1 poison 5PTB binds differentially to and alters the structures of the two duplexes, in contrast to netropsin and DAPI, which bind with similar affinities to the two duplexes and do not significantly alter their structures. These results are consistent with a mechanism for TOP1 poisoning in which drugs such as 5PTB differentially target conformationally distinct DNA sites and induce structural changes that promote enzyme-mediated DNA cleavage.
CONTEXT: In recent decades, there has been a rapid and substantial increase in tobacco consumption in China, particularly by men, but little is known from local epidemiologic studies about the pattern of smoking-related deaths. OBJECTIVE: To assess the current health effects of cigarette smoking in Shanghai, China. DESIGN: Prospective observational study of mortality in relation to cigarette smoking. SETTING: Eleven factories in urban Shanghai. SUBJECTS: A total of 9351 adults (6494 men and 2857 women) aged 35 to 64 years at baseline survey during the 1970s. OUTCOME MEASURES: All-cause and cause-specific mortality. RESULTS: During an average follow-up of 16 years, 881 men and 207 women died. Among men, 61% had described themselves as current cigarette smokers at baseline, and their overall mortality was significantly greater than that of nonsmokers (relative risk [RR], 1.4; 95% confidence interval [CI], 1.2-1.7; P<.001). The excess was almost twice as great (RR, 1.8; 95% CI, 1.5-2.2 [corrected]; P<.001) among the men who had begun smoking before the age of 25 years and was significantly associated with the number of cigarettes smoked (P<.001 for trend) after adjustment for other major risk factors. The chief sources of the excess were lung cancer (RR, 3.8; 95% CI, 2.1-6.8; P<.001), esophageal cancer (RR, 3.6; 95% CI, 1.2-10.5; P=.02), liver cancer (RR, 2.0; 95% CI, 1.1-3.7; P=.03), coronary heart disease (RR, 1.8; 95% CI, 1.0-3.2; P=.04), and chronic obstructive pulmonary disease (RR, 2.5; 95% CI, 1.4-4.4; P<.01). Among the men in this Chinese population, about 20% (95% CI, 12%-29%) of all deaths during the study period could be attributed to cigarette smoking. Of these deaths, one third involved lung cancer, one third involved other cancers, and one third involved other diseases. Only 7% of women described themselves as current cigarette smokers at baseline, but among them there was also a statistically significant excess of overall mortality (RR, 1.7; 95% CI, 1.2-2.5; P<.01). CONCLUSIONS: Cigarette smoking is already a major cause of death in China, and among middle-aged Shanghai men, about 20% of all deaths during the 1980s were due to smoking. The excess was greatest among men who began smoking before the age of 25 years, about 47% of whom would, at 1987 mortality rates, die between the ages of 35 and 69 years (compared with only 29% of nonsmokers). These estimates reflect the consequences of past smoking patterns. The future health effects of current smoking patterns are likely to be greater because of the recent large increase in cigarette consumption, particularly at younger ages, in China.
Chaperonins assist protein folding with the consumption of ATP. They exist as multi-subunit protein assemblies comprising rings of subunits stacked back to back. In Escherichia coli, asymmetric intermediates of GroEL are formed with the co-chaperonin GroES and nucleotides bound only to one of the seven-subunit rings (the cis ring) and not to the opposing ring (the trans ring). The structure of the GroEL-GroES-(ADP)7 complex reveals how large en bloc movements of the cis ring's intermediate and apical domains enable bound GroES to stabilize a folding chamber with ADP confined to the cis ring. Elevation and twist of the apical domains double the volume of the central cavity and bury hydrophobic peptide-binding residues in the interface with GroES, as well as between GroEL subunits, leaving a hydrophilic cavity lining that is conducive to protein folding. An inward tilt of the cis equatorial domain causes an outward tilt in the trans ring that opposes the binding of a second GroES. When combined with new functional results, this negative allosteric mechanism suggests a model for an ATP-driven folding cycle that requires a double toroid.
The chaperonin GroEL is a double-ring structure with a central cavity in each ring that provides an environment for the efficient folding of proteins when capped by the co-chaperone GroES in the presence of adenine nucleotides. Productive folding of the substrate rhodanese has been observed in cis ternary complexes, where GroES and polypeptide are bound to the same ring, formed with either ATP, ADP or non-hydrolysable ATP analogues, suggesting that the specific requirement for ATP is confined to an action in the trans ring that evicts GroES and polypeptide from the cis side. We show here, however, that for the folding of malate dehydrogenase and Rubisco there is also an absolute requirement for ATP in the cis ring, as ADP and AMP-PNP are unable to promote folding. We investigated the specific roles of binding and hydrolysis of ATP in the cis and trans rings using mutant forms of GroEL that bind ATP but are defective in its hydrolysis. Binding of ATP and GroES in cis initiated productive folding inside a highly stable GroEL-ATP-GroES complex. To discharge GroES and polypeptide, ATP hydrolysis in the cis ring was required to form a GroEL-ADP-GroES complex with decreased stability, priming the cis complex for release by ATP binding (without hydrolysis) in the trans ring. These observations offer an explanation of why GroEL functions as a double-ring complex.
The dc field rheological properties and frequency dependent dielectric properties of a set of electrorheological (ER) fluids composed of oxidized polyacrylonitrile or aluminosilicate materials dispersed in silicone oil were examined in this paper. Our experimental investigations show that there is a complicated relationship between the dielectric properties of dispersed particles and the ER effect. The dielectric loss of dispersed particles, which has not attracted much attention in previous work, was found to play a considerable role in ER response. The large dielectric loss tangent, experimentally around 0.10 at 1000 Hz, is found to be needed for a strong ER effect. A good ER solid material should first have large dielectric loss, and then the higher the dielectric constant, the stronger the ER effect. The large dielectric loss would facilitate the turning of dispersed particles, and the high dielectric constant would maintain the fibrillation structure stable and strong. Two processes, the particle turning process and the particle polarization process, are thought to be involved in ER activity. Our findings, in connection with the Wagner model, can better explain why the strongest ER effect occurs at particle conductivity of 10(-7) S/m; why the shear stress of some ER fluids decreases with frequency while with others the shear stress increases with frequency; and why trace water can enhance the ER effect considerably, which would help in understanding the mechanism of the ER effect. Too large a dielectric loss is thought to be unfavorable for the ER effect, and its suitable range is worth further study. The results also present a method of designing high performance ER fluids, which would significantly promote development of electrorheology and its application in industrial areas.
The heme-regulated eIF-2alpha kinase (HRI) is activated not only in heme-deficient rabbit reticulocyte lysates (RRL), but also in hemin-supplemented RRL treated with heat-shock, N-ethylmaleimide (MalNEt) or heavy metal ions. We have demonstrated previously that heat-shock proteins, Hsp90, Hsp70 and FKBP52, are associated with HRI in RRL; the association of HRI with Hsp90 and FKBP52, but not Hsp70, is enhanced by hemin. To study the role of Hsp90 and its associated cohorts in the regulation of HRI, we examined the interaction of these proteins with HRI in hemin-supplemented RRLs during heat or oxidative stress. The association of HRI with Hsp90, FKBP52 and p23 was maintained in heat-, MalNEt- or Hg2(+)-treated hemin-supplemented RRL. Glycerol gradient centrifugation and gel filtration on Sephacryl S-300 indicated that neither heat shock nor MalNEt-treatment affected the apparent molecular mass of HRI in hemin supplemented RRL. In addition, active HRI was coimmunoprecipitated with 8D3 anti-Hsp90 from both heme-deficient and MalNEt-treated hemin-supplemented RRL. These results demonstrate that activation of HRI in response to heat stress and oxidative stress does not require dissociation of Hsp90 from HRI. Furthermore, HRI activity was inhibited upon addition of hemin to Hsp90-depleted heme-deficient RRL, indicating that inhibition of HRI activity by hemin is not mediated by the reassociation of Hsp90 with HRI. We also examined the dynamics of the interaction of Hsp90 with HRI. Reconstitution of the interaction of Hsp90 with HRI was stimulated by elevated temperature and required both Mg2+ and ATP. Addition of purified Hsp90 to hemin-supplemented RRL which had been treated with MalNEt to inactivate its capacity to chaperone protein renaturation, protected HRI from irreversible denaturation and aggregation upon incubation at 41 degrees C. Our results suggest that Hsp90 interacts with HRI primarily in its capacity as a molecular chaperone, stabilizing HRI from denaturation under conditions of heat stress and oxidative stress.
Saccharomyces cerevisiae vacuole inheritance requires two low molecular weight activities, LMA1 and LMA2. LMA1 is a heterodimer of thioredoxin and protease B inhibitor 2 (I2B). Here we show that the second low molecular weight activity (LMA2) is monomeric I2B. Though LMA2/I2B was initially identified as a protease B inhibitor, this protease inhibitor activity is not related to its ability to promote vacuole fusion: (i) Low Mr protease B inhibitors cannot substitute for LMA1 or LMA 2, (ii) LMA1 and LMA2 promote the fusion of vacuoles from a strain that has no protease B, (iii) low concentrations of LMA2 that fully inhibit protease B do not promote vacuole fusion, and (iv) LMA1, in which I2B is complexed with thioredoxin, is far more active than LMA2/I2B in promoting vacuole fusion and far less active in inhibiting protease B. These studies establish a new function for I2B.
Early in S phase, the vacuole (lysosome) of Saccharomyces cerevisiae projects a stream of vesicles and membranous tubules into the bud where they fuse and establish the daughter vacuole. This inheritance reaction can be studied in vitro with isolated vacuoles. Rapid and efficient homotypic fusion between salt-washed vacuoles requires the addition of only two purified soluble proteins, Sec18p (NSF) and LMA1, a novel heterodimer with a thioredoxin subunit. We now report the identity of the second subunit of LMA1 as I(B)2, a previously identified cytosolic inhibitor of vacuolar proteinase B. Both subunits are needed for efficient vacuole inheritance in vivo and for the LMA1 activity in cell extracts. Each subunit acts via a novel mechanism, as the thioredoxin subunit is not acting through redox chemistry and LMA1 is still needed for the fusion of vacuoles which do not contain proteinase B. Both Sec18p and LMA1 act at an early stage of the in vitro reaction. Though LMA1 does not stimulate Sec18p-mediated Sec17p release, LMA1 cannot fulfill its function before Sec18p. Upon Sec17p/Sec18p action, vacuoles become labile but are rapidly stabilized by LMA1. The action of LMA1 and Sec18p is thus coupled and ordered. These data establish LMA1 as a novel factor in trafficking of yeast vacuoles.
Acidosis elicited during myocardial ischemia is a significant pathophysiological condition markedly affecting the electrical and contractile properties of heart muscle. We examined the effects of protons on K channel activity in rat ventricular myocytes by recording transient outward (Ito) and inward rectifier (IKl) K+ currents using the whole cell, voltage clamp technique. Proton concentration was controlled by independently varying the pH of HEPES-buffered external (pHo) or pipette (pHp) solutions. Mean Ito density in myocytes preconditioned in acidic external solution (pHo 6.0) for 15-20 min was significantly less than control cells equilibrated at physiological pHo. In contrast, IKl was not changed during this period of acidosis. External acidification did not decrease Ito when initiated after intracellular dialysis with standard pHp 7.2. However, when myocytes were dialyzed with acidic pHp, Ito density was significantly less than control, while alkaline pHp had little effect. Despite marked reduction in current density produced by low pHp solutions, steady-state activation and inactivation parameters of Ito were not significantly altered. In addition, the reversal potential of this current, kinetics of inactivation, and recovery from inactivation were not significantly affected by acidic or alkaline pHp solutions. Acidic pHp alone did not change IKl density compared with control, but when combined with Na+/H+ exchange blockade with 5-(N,N-dimethyl)-amiloride or Na(+)-free external solution, IKl density was significantly reduced. Our data suggest that protons inhibit Ito predominantly from the intracellular side of the channel, possibly by altering its conductance or gating properties. Moreover, intracellular protons differentially affect Ito and IKl channels, with the former exhibiting greater sensitivity for a given level of acidosis.
The present study examined changes in electrophysiological properties of ventricular myocytes isolated from rabbit hearts after 2-3 weeks of rapid ventricular pacing. Left ventricular end-diastolic pressure at completion of the pacing period was nearly four-fold greater than in age-matched controls, although there was no significant change in heart weight/body weight ratio. Action potentials recorded in current-clamp mode at low stimulation frequencies were significantly longer in duration and phase 1 diminished in isolated myocytes from paced hearts compared with control. In voltage-clamp experiments. L-type Ca2+ current (ICa) density was not different between groups of myocytes, but the maximum current (at + 10 mV) elicited by 10 microM isoproterenol was approximately 40% less in myocytes from paced hearts. In contrast, maximum ICa elicited by 10 microM forskolin was similar in both groups. The 4-aminopyridine-sensitive transient outward current (Ito) was 65% less (at + 60 mV) in myocytes from paced hearts than from control. However, after approximately 24 h in culture, Ito density in these myocytes returned toward control values. Despite marked reduction in Ito density, the inward rectifier current (IK1) was not different between groups. These data demonstrate that Ito is significantly and reversibly decreased in myocytes from rapidly paced hearts, which may partly account for marked changes in action potential morphology. Although basal ICa was not altered in this group of myocytes compared with control, its modulation by beta-agonists was markedly blunted, probably through a decrease in receptor density or coupling to adenylyl cyclase. These changes in myocyte K+ and Ca2+ channel behavior in paced hearts may relate to impaired contractility and arrhythmogenesis that is characteristic of the intact failing heart.
PURPOSE: To determine whether repeated screening can lead to early detection of primary liver cancer (PLC) and in turn to an improved clinical result. METHODS: In this randomized controlled study, Shanghai urban residents aged 35-55 years and with serum evidence of HBV infection or chronic liver disease were eligible for recruitment. Using cluster sampling, these subjects were allocated into two groups-the screening group and the control group: there were 8109 subjects in the screening group and 9711 in the control group. Subjects in the screening group were tested with serum AFP and real-time ultrasound every 6 months. One to four rounds of screening were completed. Liver cancer was treated according to stage at diagnosis. RESULTS: All subjects enrolled were followed up and classed at the end-point as alive without liver cancer, alive with liver cancer, dead from liver cancer, or dead from another cause. The mean follow-up was 1.2 years; total follow-up was 12,038 person-years in the screening group and 9,573 person-years in the control group. We detected 38 patients with PLC in the screening group and 18 patients with PLC in the control group. In the patients in the screening group 76.8% of patients were at a subclinical stage, and 70.6% of them underwent resection, the 1- and 2-year survival rates being 88.1% and 77.5%, respectively. However, in the control group, none of the patients was at a subclinical stage when diagnosed, none of them underwent resection, and none of them survived over 1 year. The lead time was estimated at 0.45 years. The cost of detecting PLC at an early stage was RMB 12,600 (US$1,500). CONCLUSION: The study proved that screening the high-risk population for PLC with a serum AFP test and real-time ultrasound examination can detect patients in the early stages, increase the resection rate and prolong the survival time. It is therefore recommended that screening for PLC be advocated in any high-risk area.
To evaluate the effect of amino acid cardioplegia on myocardial metabolism and function of ischemic canine heart, canine cardiopulmonary bypass (CPB) model was established and the dog heart was subjected to a 120 min ischemic arrest. Animals were divided into 3 groups, group 1: warm blood cardioplegia induction and terminal perfusion plus 4 C ST. Thomas hospital solution (STS) during ischemia; group 2: warm blood cardioplegia enriched with amino acid (L-asparte and L-glutamate 13 mmol/L each) and STS without amino acid (A. G.) and group 3: both warm blood cardioplegic solution and STS enriched with A. G. . The result demonstrated that the cardiac function of animals in group 2 and 3 had a significantly better recovery after ischemic-re-perfusion. By the end of ischemia the content of myocardial ATP in group 3 was distinctly higher than that in group 1 (P < 0.05), with the release of cardiac enzyme being the least. Myocardial ultra-structure almost remained intact before and after ischemia. Our experiment suggests that the cardioplegia arrest with warm blood and cold crystalloid solution enriched with amino acids could diminish the ischemia-re-perfusion injuries of the heart and enhance the effect of myocardial protection.
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The first stage of information processing in the electrosensory system involves the encoding of local changes in transdermal potential into trains of action potentials in primary electrosensory afferent nerve fibers. To develop a quantitative model of this encoding process for P-type (probability-coding) afferent fibers in the weakly electric fish Apteronotus leptorhynchus, we recorded single unit activity from electrosensory afferent axons in the posterior branch of the anterior lateral line nerve and analyzed responses to electronically generated sinusoidal amplitude modulations of the local transdermal potential. Over a range of AM frequencies from 0.1 to 200 Hz, the modulation transfer function of P-type afferents is high-pass in character, with a gain that increases monotonically up to AM frequencies of 100 Hz where it begins to roll off, and a phase advance with a range of 15-60 degrees. Based on quantitative analysis of the observed gain and phase characteristics, we present a computationally efficient model of P-type afferent response dynamics which accurately characterizes changes in afferent firing rate in response to amplitude modulations of the fish's own electric organ discharge over a wide range of AM frequencies relevant to active electrolocation.
Stress waves generated by lasers and extracorporeal lithotripters have been shown to transiently increase the permeability of the plasma membrane, without affecting cell viability. Molecules present in the medium can diffuse into the cytoplasm under the concentration gradient. Molecular uptake under stress waves correlates with the presence of functioning aquaporins in the plasma membrane.
The interactions between dizocipline, an N-methyl-D-aspartate open channel antagonist, and the induction of water drinking and c-fos expression by intracerebroventricular (i.c.v.) infusion of angiotensin II have been studied. Pretreating male rats with i.c.v. dizocilpine maleate (100 or 300 nmol) or tenocyclidine (150 nmol), both non-competitive N-methyl-D-aspartate antagonists, inhibited the subsequent dipsogenic response to i.c.v. angiotensin II (125 or 50 pmol, 5-10 min later). Dizocilpine also decreased the angiotensin II-evoked expression of c-fos in the median preoptic nucleus, supraoptic nucleus and the medial (parvicellular) and lateral (magnocellular) parts of the hypothalamic paraventricular nucleus, as well as in the nucleus of the solitary tract and the lateral parabrachial nucleus. Double staining showed that suppression of c-fos expression occurred in N-methyl-D-aspartate R1 receptor containing neurons in the hypothalamus. Pretreating rats with any of three competitive glutamate antagonists (2-amino-5-phosphonopentanoic acid, 60 or 160 nmol; gamma-D-glutamylglyine, 400 nmol; (DL-3/(R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid, 0.1 nmol) or the glycine site antagonist 7-chlorokynurenic acid had no effects on angiotensin II-induced drinking. Neither did pretreating rats with the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid antagonist 6-cyano-7-nitroquinoxaline-2,3-dione [two infusions, 30 min (240 nmol) and 5 min (160 nmol) before angiotensin II]. To eliminate cross-reactivity of dizocilpine with nicotinic receptors, animals were pretreated with nicotinic acetylcholine blocker mecamylamine (250 nmol, i.c.v.), but this had no effect on angiotensin II-dependent drinking or c-fos expression. These results suggest that an N-methyl-D-aspartate-type glutamate receptor is implicated in the dipsogenic and cellular responses to i.c.v. angiotensin II, and point to the existence of a novel set of interactions between excitatory amino acids and this neuropeptide.
Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) technique (L. Frydman and J.S. Harwood, J. Am. Chem. Soc., 117 (1995) 5367) are compared with Dynamic-Angle Spinning (DAS). Examples of MQMAS spectra are shown for I = 3/2 nuclei with CQ up to 3.6 MHz, and for 27Al (I = 5/2) with CQ up to 10 MHz. The MQMAS linewidth is largely independent of the magnitude of the homonuclear dipolar interaction, while the spinning sideband manifold is similar to that observed in DAS experiments. MQMAS is technically simple and routinely useful for studying nuclei with short spin-lattice relaxation times, but care must be taken in its use for quantitative studies as the excitation of the triple-quantum coherence is not uniform. In this regard, MQMAS is most useful for samples with small quadrupolar coupling constants. In the specific case of 17O, DAS would give spectra with excellent resolution in comparison to MQMAS. The different advantages of DAS and MQMAS make them useful complementary techniques in many cases. Two additional methods are also presented for extracting the chemical shift anisotropy (CSA) directly for quadrupolar nuclei using the multiple-quantum scheme.