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Biomedical subjects

B Xu

Publications and source records attributed to B Xu.

At least 19 recordsLinked to original sources
PubMed1992

Assignment of a yeast protein necessary for mitochondrial transcription initiation.

Yeast mitochondrial DNA contains multiple promoters that are responsible for expression of its genes. The basic yeast mitochondrial promoter consists of a nonanucleotide consensus sequence [5'-ATATAAGTA(+1)-3'] that must be recognized by transcription proteins, including mitochondrial RNA polymerase and any relevant trans-acting factors. Since mitochondrial RNA polymerase alone appeared unable to recognize a mitochondrial promoter, we examined the effects of providing accessory proteins to enable promoter function. After expression in Escherichia coli or purification from yeast mitochondria, two proteins were tested; they were ABF2 (a structural homologue of the human mitochondrial transcriptional activator mtTF1) and MTF1 (the gene product of a yeast locus known to exhibit a mitochondrial transcription phenotype). The results show that MTF1 specifies correct transcriptional initiation while ABF2 does not. We conclude that MTF1 is an essential key protein in yeast mitochondrial promoter function. Considering the increasing complexity of the mitochondrial transcription apparatus, we propose a nomenclature system for its components.

Base Sequence↗
PubMed1992

Baculovirus phosphoprotein pp31 is associated with virogenic stroma.

The PstI K fragment of Autographa californica nuclear polyhedrosis virus (AcMNPV) encodes a protein with a molecular weight of 31,000. To define the role of this protein (pp31) in virus infection further, it was overexpressed in bacteria and used to produce polyclonal antiserum. Radioimmunoprecipitation analysis indicated that pp31 was synthesized during both the early and late phases of virus infection, consistent with previous analyses indicating that the gene was regulated by tandem early and late promoters. Metabolic labeling of cells with carrier-free phosphate indicated that pp31 was phosphorylated. Biochemical fractionation experiments showed that pp31 was localized in the nucleus and that it was more stably associated with the nucleus at later times of infection. Immunoblot analysis of subnuclear fractions indicated that pp31 was associated predominantly with the chromatin and nuclear matrix fractions. Immunofluorescence experiments confirmed that the pp31 protein was localized in the nucleus. Nuclear staining was relatively uniform early but was more centrally nuclear later in infection. Immunoelectron microscopy indicated that the pp31 protein was a component of virogenic stroma. Southwestern (DNA-protein) blot analysis demonstrated that pp31 is a DNA-binding protein. These findings suggest a possible role for pp31 in the virus life cycle.

Animals↗
PubMed1992

[Effects of zinc deficiency and vitamin D deficiency on bone calcification and development of rats].

Zinc deficiency rat model was made by feeding zinc deficiency diet. The level of bone calcium of the zinc deficiency rats was significantly lower than that of the control rats. Their bone cortex was thinner and bone density decreased. The counts of their cartilage cells and hypertrophic cells of epiphyseal plate were less frequent, and the diameter of their hypertrophic cells was smaller than that of the controls. It suggested that zinc deficiency caused defective bone calcification which was similar to that in vitamin D deficiency. Zinc deficiency seemed to hinder the linear growth of long bone and might be the cause of dwarf.

Animals↗
PubMed1992

[Studies on the establishment of malarial animal model of short-term relapse. I. Asynchronous growth of exoerythrocytic schizonts of Plasmodium cynomolgi].

A monkey was infected with sporozoites of Plasmodium cynomolgi from Vietnam. Parasitemia was detected on the 8th day with a starting density of 17/100 white blood cells. 22 hours after that time, many EE schizonts appeared with an average density of 3.74 +/- 0.66 per mm3 hepatic tissue in liver biopsy specimens from the monkey. Most of the EE schizonts were immature and grew at an uneven rate, having an average diameter of 34.22 +/- 7.28 microns but some of them even remained 15.75 +/- 2.47 microns in diameter similar to the EE schizonts on the 6th day. The results showed that the EE schizonts of Plasmodium cynomologi were asynchronous in growth. The authors suggest that the release of merozoites from liver might be a successive process for many times, and not to be completed at a time.

Animals↗
PubMed1992

[Role of the central alpha-receptors in the modulation of carotid sinus reflex of rats].

To investigate the effects of the central alpha-receptors on the carotid sinus reflex, phenoxybenzamine (PBZ, 2 micrograms/20 microliters) or yohimbine (Y, 2 micrograms/20 microliters) was injected into the lateral cerebral ventricle (LCV) and intracarotid sinus pressure (ISP)-mean arterial pressure (MAP) relationship curve was constructed and fitted by a Logistic function. The results were as follows: (1) After injection of PBZ into LCV, the ISP-MAP relationship curve shifted upward at a higher ISP level with decreased peak slope and MAP range while the ISP-slope curve shifted downward. (2) After injection of Y into LCV, the ISP-MAP relationship curve shifted upward at a higher ISP level with decreased peak slope and MAP range and increased threshold. The ISP-slope curve shifted downward significantly at 10.64, 15.96 kPa. The peak slope and MAP range of Y group decreased significantly as compared with that of the PBZ group. These results indicated that after blockage of central alpha-receptors the sensitivity of the sinus reflex decreased significantly, and the blockage action of alpha 2-receptor is greater than that of alpha 1-receptor.

Animals↗
PubMed1992

[Effect of the central noradrenergic system on carotid sinus reflex in rats].

In order to study the effect of central noradrenergic system on the regulation of mean arterial pressure (MAP) by intracarotid sinus pressure (ISP), ISP-MAP relationship curves were constructed using isolated carotid sinus under the condition of injection of 6-OHDA (200 micrograms) into lateral ventricle or cauterization of locus coeruleus (LC) and compared with that obtained under the condition of control. All ISP-MAP curves can be fitted by a logistic functional plot whose characteristics can be defined by two parameters, i.e. coordinates of the inversion point of the slope of the curve and the MAP range related to the rate of change of slope factor with which carotid sinus pressure exerts its control. The results were as follows: After injection of 6-OHDA, the rate of change of the slope of the ISP-MAP curve is considerably slower than that of the normal control, thus showing a much compressed range of MAP by ISP, while the abscissa (i.e. position of ISP) of the slope inversion point of the curve shows practically no change. In comparison with the control, cauterization of LC causes a similar but less striking change of ISP-MAP curve than that of 6-OHDA injection experiment. All such differences were illustrated in Fig. 3. The above results indicated that the central noradrenergic system facilitates carotid sinus reflex and LC plays a dominant role.

Adrenergic Fibers↗
PubMed1991

Iron oxidation chemistry in ferritin. Increasing Fe/O2 stoichiometry during core formation.

The origin of previously observed variations in stoichiometry of iron oxidation during the oxidative deposition of iron in ferritin has been poorly understood. Knowledge of the stoichiometry of Fe(II) oxidation by O2 is essential to establishing the mechanism of iron core formation. In the present work, the amount of Fe(II) oxidized was measured by Mössbauer spectrometry and the O2 consumed by mass spectrometry. The number of protons produced in the reaction was measured by "pH stat" titration and hydrogen peroxide production by the effect of the enzyme catalase on the measured stoichiometry. For protein samples containing low levels of iron (24 Fe(II)/protein) the stoichiometry was found to be 1.95 +/- 0.18 Fe(II)/O2 with H2O2 being a product, viz. Equation 1. 2Fe2+ + O2 + 4H2O----2FeOOH + H2O2 + 4H+ (1) EPR spin trapping experiments showed no evidence of superoxide radical formation. The stoichiometry markedly increased with additional iron (240-960 Fe/protein), to a value of 4 Fe(II)/O2 as in Equation 2. 4Fe2+ + O2 + 6H2O----4FeOOH + 8H+ (2) As the iron core is progressively laid down, the mechanism of iron oxidation changes from a protein dominated process with H2O2 being the primary product of O2 reduction to a mineral surface dominated process where H2O is the primary product. These results emphasize the importance of the apoferritin shell in facilitating iron oxidation in the early stage of iron deposition prior to significant development of the polynuclear iron core.

Animals↗
PubMed1991

Inhibition of cellular thymidylate synthesis by cytotoxic propenal derivatives of pyrimidine bases and deoxynucleosides.

A series of cytotoxic propenal (3-oxoprop-1-enyl) derivatives of pyrimidine bases and deoxynucleosides was evaluated for their ability to block thymidylate synthesis in intact and permeabilized murine leukemia L1210 cells. Several were potent inhibitors of this process, likely contributing to their cytotoxicity. The IC50 values of thymidine-3-propenal, the prototype of this series, in intact and permeabilized L1210, L-M and L-M(TK-) cells were 21, 7.5, and 75 microM and 1.5, 1.7, and 3.5 microM, respectively. The related base analogue, thymine-1-propenal, is a product of bleomycin-induced DNA strand-scission; the results of the present study bear on the mode of action of this antibiotic.

Acrolein↗
PubMed1991

A computer-assisted image processing method for determining relative cardiac function in the chick embryo.

The general objective of this study was to develop a noninvasive method for efficiently and reproducibly determining relative cardiac function parameters in the chick embryo. The specific objectives of the study were 1) to develop several methods for computer-assisted image processing and quantitation of relative intraventricular blood volumes in the 3-day-old embryonic chick heart and 2) to compare methods for precision and with a previously established manual processing method. Images of the embryonic chick heart in ovo were recorded on videocassette tape, digitized, and enhanced by computer-aided histogram equalization. The area occupied by blood within the common ventricle was extracted by region-growing and spurious region removal algorithms and defined by the determination of edge-pixel coordinates. Edge-pixel coordinates of the longitudinal and transverse axes of the common ventricular blood region were located by three different methods, the lengths of the axes calculated, and volumes computed from the equation for determining volume of a prolate spheroid. Twenty-five images of the embryonic heart were randomly selected and processed. Volumes were calculated with each of the three methods on six different occasions. A coefficient of variation was calculated for each method. The intraobserver mean coefficient of variation for each method was 7.4%. When a 2-way ANOVA was conducted, mean coefficients of variation did not differ significantly for the three methods. However, computer processing (in addition to significantly reducing the time required to generate data) reduced the coefficient of variation observed in manual processing by 56.5%.

Analysis of Variance↗
PubMed1991

Efficacy of bimolane in the Malassezia ovalis model of psoriasis.

Bimolane, an analog of razoxane has been used in China with comparable efficacy but less toxicity than razoxane in the treatment of psoriasis. In an attempt to characterize further its mode of action it was administered both systemically and topically in the Malassezia ovalis animal model of psoriasis. Intravenous methotrexate and topical 0.1% betamethasone valerate were also used as positive control treatments. The animal model of psoriasis was effectively treated by bimolane, both systemically and topically, and also by parenteral methotrexate and topical betamethasone valerate. The time course of bimolane's effect with this model was different from methotrexate's suggesting the possibility of a different mode of action. Because bimolane, like razoxane, is an ethylene diamino tetraacetate acid (EDTA) derivative, it is possible that its effects on this reaction relate to its chelating properties and that inhibition of complement activation is important to its mode of action.

Administration, Cutaneous↗
PubMed1991

Recent advances in pharmacologic study of natural anticancer agents in China.

In this paper a number of anticancer agents of natural origin will be presented. Hydroxycamptothecin (HCPT) was found to produce a strong inhibitory action on a variety of animal tumors. It is also effective for treatment of patients with gastric carcinoma, liver carcinoma, tumor of head and neck or leukemia. Pharmacologic studies showed that it could depress S phase of tumor cells significantly and cause formation of cellular chromatid breaks. By means of alkaline elution and nick translation methods it has been proved that HCPT induced DNA single strand breaks remarkably. Homoharringtonine (HHRT) was shown to be effective against acute leukemia. Recent experiments in tumor-bearing mice indicated that (HHRT) could diminish tumor metastasis. Using molecular hybridization technique it was demonstrated that (HHRT) decreased the content of c-myc RNA in the cytoplasm but not in the nuclei. Lycobetaine (LBT) possessed strong inhibitory effects on a number of ascites tumors. In clinical trials it was effective against ovarian and gastric carcinomas. It is able to intercalate into DNA. Oxalysine (OXL) is a new antibiotic and shown to be effective against tumor metastatis. When used in combination with 5-FU, its anticancer action could be enhanced. Other natural compounds such as indirubin, beta-elemene, irisquinone, oridonine, norcantharidin and PSP have been also found to possess antitumor action.

Animals↗
PubMed1991

[Methanogens from feces of patients with intestine disorder].

Fecal specimens from 10 colorectal cancer, 1 duodenum diverticulosis and 2 healthy adults were examined. Nine fecal enrichments contained Methanobrevibacter. The percentage of methanogen positive individuals was 69% Methanobrevibacter were isolated from fecal enrichments of 4 colorectal cancer and 1 duodenum diverticulosis. The percentage of breath methane positive individuals and methane production had significantly increased in colorectal cancer patients. It will be hopeful that methane production in breath samples at the end of exhalation will became a rapid, simple and non-penetrative method for monitoring precancerous colonic or rectal carcinogenesis and monitoring the relapse of individuals with carcinosectomy.

Breath Tests↗
PubMed1990

[Modulation of norepinephrine release in sympathetic nerve endings in renal hypertensive dogs].

Experimental renal hypertensive and normal dogs with femoral arteries constantly perfused were studied. Cocaine was used to block the presynaptic norepinephrine (NE) reuptake and tyramine to initiate the release of NE in sympathetic nerve endings. NE spillover and infusion pressure were measured under basic conditions and during intraarterial infusion of cocaine, tyramine and in combination with alpha 1 and alpha 2 adrenoceptor antagonists. The extent of NE spillover increase induced by infusion of tyramine, the increased infusion pressure by cocaine and tyramine, and the reduced infusion pressure by prazosin were all greater in hypertensive dogs than those in normal dogs, but adrenoceptor antagonist idazoxan further increased tyramine-induced NE spillover in normal dogs only. It was suggested that reduced-regulation of presynaptic alpha 2 adrenoceptors to NE release and increased responsiveness of postsynaptic alpha 1 adrenoceptors to NE were present in hypertensive dogs.

Adrenergic alpha-Antagonists↗
PubMed1990

[Analgesic and antipyretic effects of cyproheptadine].

Cyproheptadine-HCl raised the pain thresholds during hot plat test and writhing test in mice and tail flick test in rats, strengthened the hypnotic action by subthreshold dosage of sodium pentobarbital and chloral hydrate. The ED50 were 4.4 (3.2-5.7) and 12.4 (8.4-18.2) mg/kg 30 min after ip cyproheptadine in mice and rats, respectively. The ED50 was 0.14 (0.12-0.18) mg/kg 90 min after icv cyproheptadine in mice. Cyproheptadine po 20, 40 mg/kg and ip 10, 20 mg/kg showed significant antipyretic effects on yeast-induced pyrexia in rats.

Animals↗
PubMed1990

[Frequency- and voltage-dependent effects of changrolin on maximal upstroke velocity of action potentials in guinea pig papillary muscles].

Changrolin (CRL) is a new antiarrhythmic drug originated in China in 1970s. The effects of CRL on maximal upstroke velocity (Vmax) of action potentials were studied with standard microelectrode and computer in guinea pig papillary muscles. CRL depressed the Vmax. This effect was dependent on the rate of stimulations. The onset of use-dependent depression was monoexponential and dependent on drug concentration and rate of stimulations. The rate of recovery from use-dependent depression also followed a single exponential time course. CRL shifted the curve relating normalized Vmax to membrane potential in the hyperpolarizing direction. The onset rate was 0.156 +/- 0.025 AP-1 (RDB 50%), and offset rate (tau r) was 4.7 +/- 0.9 s. These suggest that CRL belongs to class Ia antiarrhythmic drugs.

Action Potentials↗