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J Xiong

Publications and source records attributed to J Xiong.

107 records · Page 6Linked to original sources
PubMed1991

Substitution of asparagine for serine-406 of the immunoglobulin mu heavy chain alters glycosylation at asparagine-402.

Previous work suggested that the substitution of Asn for Ser at position 406 of the mu heavy chain of mouse IgM results in aberrant glycosylation at Asn402. In order to characterise the apparently abnormal glycosylation process more precisely, the mutant and wildtype mu chains were fragmented by cleavage with cyanogen bromide, and the resulting glycopeptides were analysed further. Measurements of lectin binding specificity as well as glycosidase sensitivity suggest that the oligosaccharide at Asn402 of wildtype mu is a hybrid type which does not contain terminal alpha(2-6) or alpha(2-3) linked sialic acid. By contrast, the corresponding oligosaccharide on Asn402 of mutant mu is complex and contains terminal sialic acid linked alpha(2-6) to galactose. The structural features for specifying the abnormal glycosylation are present in monomeric mutant IgM.

Amino Acid Sequence↗
PubMed1991

GdDTPA-enhanced magnetic resonance imaging of the aqueous flow in the rabbit eye.

Magnetic resonance imaging with gadolinium-diethylenetriaminepentaacetic acid complex (GdDTPA) as the contrast agent was used to image the aqueous chamber of the eye. This method, in addition to providing spatial information, permits quantitative study of the aqueous flow. GdDTPA solution was applied either topically or intravenously, entering the anterior chamber via different pathways. The wash-in and wash-out of GdDTPA follow a two-compartment model which enables determination of the aqueous flow rate by multiplying the aqueous chamber volume by the wash-out rate constant. Rabbit eyes showed a flow rate of 1.5-2 microliters/min which was retarded by the systemic administration of acetazolamide (Diamox).

Acetazolamide↗
PubMed1991

Measurement of water movement in the rabbit eye in vivo using H2(17)O.

Topically applied (eyedrop) H2(17)O (10% enrichment) was used in magnetic resonance studies to quantify intraocular water dispersion in vivo. The rate of H2(17)O removed from the aqueous chamber is in the order of 0.1 ml/min/ml of tissue. Similar results are obtained with either proton imaging or 17O spectroscopy. Parallel experiments of direct injection of H2(17)O into the aqueous chamber supported the topical data. Proton MR imaging of H2(17)O dissipation from the aqueous chamber with clinical imagers, coupled with eyedrop application, suggests clinical possibilities.

Animals↗
PubMed1991

Water movement in the rabbit eye.

The intraocular distribution of topically applied D2O was quantified using deuterium nuclear magnetic resonance (NMR) spectroscopy. D2O appeared in all tissues with the highest concentration in the aqueous humor (1.2 M); however, it rapidly dissipated from the eye. Surface coil NMR spectroscopy on D2O-treated eyes in vivo showed that the flow pattern was best described by a single exponential decay plus a constant. This suggests that the D2O flow consisted of a flow component representing vascular circulation (with a flow rate constant of 0.101 min-1), and a reservoir-like component. Topical D2O in conjunction with the surface-coil NMR technique can be used to examine the movement of water in the anterior segment of the living eye.

Animals↗
PubMed1991

Analysis of concurrent glucose consumption by the hexose monophosphate shunt, glycolysis, and the polyol pathway in the crystalline lens.

A method based on 13C-NMR spectroscopy is described, in which the metabolism of [13C2]glucose was assessed in intact rat lenses. By analysing the ratio of 13C3/(13C2 + 13C3) lactate, a quantitative measurement of the hexose monophosphate shunt (HMPS) activity could be derived. Similarly, measurements of the time-dependent increase of lactate and sorbitol permitted the determination of the activity of the Embden-Meyerhof pathway and the polyol pathway, respectively. This method offers significant advantages over other biochemical and spectroscopic methods and allows for the first time a direct correlation between the activities of the polyol pathway and the HMPS.

Animals↗
PubMed1991

Purification and Developmental Analysis of a Metalloendoproteinase from the Leaves of Glycine max.

A metalloendoproteinase from leaves of soybean (Glycine max) has been purified 1160-fold to electrophoretic homogeneity. The native protein is monomeric with a molecular mass of 15 kilodaltons as estimated by gel filtration and 19 kilodaltons as estimated by denaturing gel electrophoresis. The enzyme has a pH optima of 8.0 to 9.0 using Azocoll as substrate. The proteolytic activity is susceptible to metal chelating agents and the inactivated enzyme can be restored to 69% of original activity by the addition of ZnCl(2). Western analysis shows that a fraction of the soybean metalloendoproteinase is present within the extracellular space of older leaves. Soybean metalloendoproteinase 1 is the Azocollase A activity first described by Ragster and Chrispeels (Plant Physiol 64: 857-862; 1979).

Journal Article↗
PubMed1990

Metabolic studies of galactosemic cataract.

Experimental diabetic and galactosemic animal models are widely used to study diabetes-induced complications. Galactose feeding can rapidly produce cataract, retinopathy and nephropathy; it is therefore favored over the diabetic model. Although the common feature for both models is the activation of aldose reductase, there are substantial differences between the two--not only does the rate of cataract progression differ but the metabolic patterns are far more complex than for polyol production alone. We here present the result of a comparison between diabetic and galactosemic lenses and show the differences in phosphorus and aldose metabolism, cell integrity and osmotic environment.

Animals↗
PubMed1989

Metabolic changes in the cornea of vitamin A-deficient rats.

We have investigated alterations of the metabolic state in vitamin A-deficient (A-) corneas using phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy. Comparing to the control, A- corneas showed a prominent rise of phosphocreatine (PCr) as well as a total loss of glycerophosphorylcholine (GPC). Further, ATP levels were lower, and sugar phosphates (SP) and inorganic phosphate (Pi) were higher than those of the control. The accumulation of PCr and Pi, and decrease of ATP indicate that the activity of creatine kinase may be altered in vitamin A deficiency. These results suggest that vitamin A may have a role in creatine kinase activation and/or induction and that its deficiency causes a decline of energy metabolism in corneal epithelium. Moreover, disappearance of GPC implies an impaired cellular membrane metabolism. When retinyl acetate was supplied to A-rats for 5 weeks, the 31P profiles of vitamin A-repleted rat corneas recovered to normal.

Adenosine Triphosphate↗
PubMed1986

A preliminary study on the immunodiagnosis of paragonimiasis--the physico-chemical and immunological characteristics of the crude and partially purified antigens of Paragonimus westermani (Liaoning).

We have now succeeded in preparing a partially purified antigen (Fr. 1). The positive rates of the indirect ELISA were 100% both for sera of proved human cases and dogs infected with Paragonimus westermani when Fr. 1 was used, whereas the positive rates of the test were 71.4% and 75% on sera from patients and infected dogs respectively when crude antigen was used. Moreover, it is also better than the crude antigen in specificity, so a more reliable test in immunodiagnosis of paragonimiasis is available in our laboratory.

Animals↗
PubMedDate not supplied

Fast spin-echo characteristics of visual stimulation-induced signal changes in the human brain.

A fast spin-echo (FSE) technique used in a conventional MR imaging scanner has been successfully developed for obtaining functional MR images with high spatial resolution and multiple slices. Our preliminary visual stimulation studies using the FSE technique show that the nuclear MR signal increases by 2.6% during activation in the primary visual cortex. These results provide evidence that the diffusion of tissue water molecules plays a key role in determining functional MR signal amplitude. Because the FSE functional MR imaging signal is extremely sensitive to microvascular (brain capillaries) hemodynamics, the FSE technique can be a powerful tool for studying the neuronal activity of the human brain.

Adult↗
PubMedDate not supplied

The pharmacokinetics of hyperpolarized xenon: implications for cerebral MRI.

In this work, a compartmental model to predict the concentration of hyperpolarized xenon (Xe) in the brain is developed based on the well established kinetics of Xe and estimated T1 values for the compartments. For the gaseous compartments, T1 was set to 12 seconds. For the tissue compartments, T1 was set to 6 seconds. Three gas delivery techniques were modeled: hyperventilation followed by breath-hold, continual breathing, and hyperventilation followed by continual breathing. Based on Xe CT, it is estimated that the maximum concentration of Xe that could be breathed is 80%. Based on this value and the estimated maximum polarization of 50%, the peak gray matter concentration of hyperpolarized Xe is calculated to be .036 mM. This leads to an estimated signal-to-noise ratio (SNR), at 2 T, for hyperpolarized Xe that is a factor of 50 lower than the SNR for proton MRI. The peak concentration of hyperpolarized Xe was also calculated over a wide range of gas and tissue T1 values. This model also predicts that the arterial blood will have a concentration of hyperpolarized Xe that is 10 times greater than the concentration in gray matter. An interactive version of the model can be found on the World Wide Web at http:(/)/ric.uthscsa.edu/staff /charlesmartinphd.html.

Administration, Inhalation↗
PubMedDate not supplied

Solid-state 29Si, 113Cd, 119Sn, and 31P NMR studies of II-IV-P2 semiconductors.

Solid-state 29Si, 113Cd, 119Sn, and 31P MAS NMR spectra are reported on a series of II-IV-P2 compounds. In favorable cases (e.g., high degree of crystallinity, low concentration of unpaired electrons), well-defined spectra, with sharp lines for each specific nearest-neighbor configuration, are observed; in such cases, expected J coupling patterns are also seen. High-resolution solid-state NMR studies of this type provide useful information on structure (disorder), doping, and electron-mediated coupling in semiconductor systems.

Cadmium↗
PubMedDate not supplied

Lateral cerebellar hemispheres actively support sensory acquisition and discrimination rather than motor control.

This study examined a new hypothesis proposing that the lateral cerebellum is not activated by motor control per se, as widely assumed, but is engaged during the acquisition and discrimination of tactile sensory information. This proposal derives from neurobiological studies of these regions of the rat cerebellum. Magnetic resonance imaging of the lateral cerebellar output nucleus (dentate) of humans during passive and active sensory tasks confirmed four a priori implications of this hypothesis. Dentate nuclei responded to cutaneous stimuli, even when there were no accompanying overt finger movements. Finger movements not associated with tactile sensory discrimination produced no dentate activation. Sensory discrimination with the fingers induced an increase in dentate activation, with or without finger movements. Finally, dentate activity was greatest when there was the most opportunity to modulate the acquisition of the sensory tactile data: when the discrimination involved the active repositioning of tactile sensory surface of the fingers. Furthermore, activity in cerebellar cortex was strongly correlated with observed dentate activity. This distinct four-way pattern of effects strongly challenges other cerebellar theories. However, contrary to appearances, neither our hypothesis nor findings conflict with behavioral effects of cerebellar damage, neurophysiological data on animals performing motor tasks, or cerebellar contribution to nonmotor, perceptual, and cognitive tasks.

Adult↗
PubMedDate not supplied

Sequence, genomic organization, and chromosome localization of the mouse TRADD gene.

Signals triggered by tumor necrosis factor (TNF) are mediated by its two receptors: the 55 kDa TNF receptor one (TNF-R1) and the 75 kDa TNF receptor two (TNF-R2). Activation of TNF-R1 induces cell death, NF-kappa B activation, inflammatory response and anti-viral activity, while TNF-R2 mainly stimulates cell proliferation and NF-kappa B activation. The TNF-R2-associated factor TRAF2 has been shown to mediate activation of NF-kappa B by TNF-R2 and CD40. The human TNF-R1-associated death domain protein (TRADD) induces cell death and NF-kappa B activation when overexpressed. Here we describe the cloning and gene structure of the mouse homolog of TRADD. Mouse TRADD shares 75% overall amino acid sequence identity with human TRADD, suggesting high conservation of function. Mouse TRADD specifically interacts with wild type TNF-R1 but not with a truncated mutant TNF-R1 lacking its C-terminal 20 amino acids. Like human TRADD, mouse TRADD also induces activation of NF-kappa B and cell death. The expression of TRADD in mouse embryo appears developmentally regulated. The mTRADD gene contains four exons, with the fourth exon encoding all of the death domain. The mouse TRADD gene was localized to the distal region of chromosome 8.

Amino Acid Sequence↗