PubMed Health⌕ Search

Biomedical subjects

Z K Wang

Publications and source records attributed to Z K Wang.

18 recordsLinked to original sources
PubMed2026

[Intestinal microbiota alterations after digestive tract reconstruction surgery and their impacts on host physiology].

The gut microbiota, acknowledged as the human body's 'second genome', plays a pivotal role in maintaining health. Digestive tract reconstruction surgery profoundly alters the anatomical structure and physiological environment of the gastrointestinal tract, thereby inducing significant shifts in the intestinal microbiota. These microbial changes subsequently influence host physiological functions through metabolic, immune, neuroendocrine, and other pathways. For instance, Roux-en-Y gastric bypass surgery enriches short-chain fatty acid(SCFA)-producing Bacteroides, improving systemic insulin sensitivity. Conversely, pancreaticoduodenectomy leads to a marked enrichment of potential pathobionts such as Klebsiella and Clostridium, which may elevate the risk of infections and tumor recurrence. This review comprehensively summarizes the characteristic changes in the gut microbiota following various digestive tract reconstruction procedures and discusses their multifaceted impacts on host physiology, aiming to provide insights for future experimental research and clinical practice.

Humans↗
PubMed2005

Spin waves in nickel nanorings of large aspect ratio.

The spin dynamics of high-aspect-ratio nickel nanorings in a longitudinal magnetic field have been investigated by Brillouin spectroscopy and the results are compared with a macroscopic theory and three-dimensional micromagnetic simulations. Good agreement is found between the measured and calculated magnetic field dependence of the spin wave frequency. Simulations show that as the field decreases from saturation, the rings switch from a "bamboo" to a novel "twisted bamboo" state at a certain critical field, and predict a corresponding dip in the dependence of the spin wave frequency on the magnetic field.

Journal Article↗
PubMed2003

Brillouin study of the quantization of acoustic modes in nanospheres.

The vibrational modes in three-dimensional ordered arrays of unembedded SiO2 nanospheres have been studied by Brillouin light scattering. Multiple distinct Brillouin peaks are observed whose frequencies are found to be inversely proportional to the diameter (approximately 200-340 nm) of the nanospheres, in agreement with Lamb's theory. This is the first Brillouin observation of acoustic mode quantization in a nanoparticle arising from spatial confinement. The distinct spectral peaks measured afford an unambiguous assignment of seven surface and inner acoustic modes. Interestingly, the relative intensities and polarization dependence of the Brillouin spectrum do not agree with the predictions made for Raman scattering.

Journal Article↗
PubMed2002

Spin-wave quantization in ferromagnetic nickel nanowires.

The dynamical properties of uniform two-dimensional arrays of nickel nanowires have been investigated by inelastic light scattering. Multiple spin waves are observed that are in accordance with dipole-exchange theory predictions for the quantization of bulk spin waves. This first study of the spin-wave dynamics in ferromagnetic nanowire arrays reveals strong mode quantization effects and indications of a subtle magnetic interplay between nanowires. The results show that it is important to take proper account of these effects for the fundamental physics and future technological developments of magnetic nanowires.

Journal Article↗
PubMed2001

[Relationship between differential expression patterns of multigene families and heterosis in a wheat diallel crosses].

In order to understand molecular basis of heterosis, the patterns of differential gene expression of multigene families between wheat hybrids and their parents in seedling leaves were analyzed by using mRNA differential display. Relationships between differential gene expression patterns, heterosis and F1 hybrid performance were determined. Four patterns of differential gene expression were observed, which include: (1) bands observed in both parents but not in the F1; (2) bands occurring in only one parent but not in the F1 or the other parent; (3) bands detected in only the F1 but neither of the parents; (4) bands present in one parent and F1 but absent in the other parent. The analysis showed that patterns of differential gene expression were not correlated with the F1 hybrid performance for all the eight agronomic traits. However, differentially expressed fragments that occurred only in the F1 but neither of the parents were found to be positively correlated with heterosis. On the contrary, fragments observed in both parents but not in the F1 were negatively correlated with heterosis. It is concluded that the differential expression of regulatory genes plays an important role in heterosis.

Crosses, Genetic↗
PubMed2001

[Dual sieve-mesh collimator].

In this paper is advanced a new type of collimator-dual sieve-mesh collimator. Its principle is to use scanned electronic beam to attack 400 matrix-arranged wolfram targets of the square holes on the upper side of the main collimator and created 400 small X-ray fields sized by 10 mm x 10 mm. These X-ray fields will leave on its center 400 smaller X-ray fields sized by 5 mm x 5 mm after being further collimated by a sub-collimator. What's more, 16 different groups of such X-ray fields can be left on the center of the same field by controlling the all-round movement of the main collimator and sub-collimator in proper order and by scanning it round by round and mesh by mesh with electronic beams. It is these ting fields groups that make up various treatment fields with different energy (Dosage). This type of collimator can replace and simplify all other present collimators on accelerators and conformal-intensity modulation radiotherapy equipment. It has advantage of reducing the costs of radio-therapy equipment and making conformal and intensity modulation radiotherapy easier to perform.

Equipment Design↗
PubMed2001

[Dual copy-supplement collimator].

Dual Copy-Supplement Collimator consists of two lead conic sections centered on one common radioactive source and having a lot of small square holes on them. When scanning electron beams strike X-Ray target and create some X-Ray fields while passing through the primary section, they penetrate the secondary section and generate even smaller field units(FU). Using these FUs would compose various treatment fields with different energy (dosage). It is able not only to replace many existing collimators such as MLC, but also to make the conformal radiotherapy easier.

Equipment Design↗
PubMed1998

Structural studies of alpha-N-acetylgalactosaminidase: effect of glycosylation on the level of expression, secretion efficiency, and enzyme activity.

alpha-N-Acetylgalactosaminidase (alphaNAGAL, EC 3.2.1.49) is an exoglycosidase specific for the hydrolysis of terminal alpha-linked N-acetylgalactosamine from oligosaccharide chains. After cloning of its cDNA, the recombinant alphaNAGAL (ralphaNAGAL) was produced in Pichia pastoris, a methylotrophic yeast strain. The enzyme was hyperglycosylated by the host cells, resulting in a protein with a molecular mass of approximately 50 kDa, which was 7 kDa larger than that of its native counterpart. When deglycosylated with endoglycosidase H under nondenaturing conditions, ralphaNAGAL remained fully active, suggesting that the glycosylation is not required for enzyme activity. Data derived from mass spectrometry indicated that all three putative N-glycosylation sites [Asn residues at positions 161 (N1), 185 (N2), and 369 (N3)] in the enzyme were glycosylated, and a high-mannose structure, which was possibly phosphorylated, was attached to the sites N1 and N2. In order to examine the effect of individual N-linked oligosaccharide chains on the expression of ralphaNAGAL in P. pastoris, we mutated each of the N-glycosylation sites, as well as all three sites in the same protein molecule, by substituting the Asn with a Gln residue. The results indicate that ralphaNAGAL mutations in any of the three glycosylation sites, N2 being the most profound, impaired the expression level, altered subcellular distribution, and decreased the efficiency of secretion. Our data suggest that the N-glycosylation of ralphaNAGAL expressed in P. pastoris may be important in protein folding and resistance to protease degradation during protein synthesis, although it is apparently not required for enzyme activity.

Animals↗
PubMed1996

Trp-16 is essential for the activity of alpha-galactosidase and alpha-N-acetylgalactosaminidase.

By expressing site-directed mutants in the methylotrophic yeast strain Pichia pastoris, the role of a tryptophan residue at position 16 in the activity of alpha-galactosidase and alpha-N-acetylgalactosaminidase, two closely related exoglycosidases, was studied. A substitution of Trp-16 with an arginine residue in alpha-N-acetylgalactosaminidase abolished the enzyme activity, which was confirmed by replacing a 600 bp fragment containing the mutation with the corresponding wild-type sequence. The same tryptophan residue was then substituted with an alanine in both enzymes by site-directed mutagenesis to reveal a possible relationship between their active sites. The purified alpha-N-acetylgalactosaminidase mutant demonstrated a specific activity of 2.8 x 10(-2) U/mg and a Vmax/K(m) of 4.3 x 10(-2), which were both more than a thousandfold lower than corresponding values for the wild-type enzyme. Furthermore, the mutant failed to bind to an affinity resin, suggesting the involvement of Trp-16 in substrate-binding. In addition, the purified alpha-galactosidase mutant resulted in more than a 10(4)-fold decrease in specific activity. Thus our data suggest that Trp-16 in both alpha-galactosidase and alpha-N-acetylgalactosaminidase is critical for enzymatic activity, which in turn supports the hypothesis that these two enzymes may share a catalytic mechanism involving similar residues in their active sites.

Animals↗
PubMed1996

Expression and characterization of recombinant alpha-galactosidase in baculovirus-infected insect cells.

A cDNA encoding coffee bean alpha-galactosidase was subcloned into baculovirus expression vectors, pVL-1393 and pAc-GP67B, for intracellular and extracellular expression in Spodoptera frugiperda (Sf9) insect cells, respectively. The expressed protein (recombinant alpha-galactosidase) was immunologically reactive with antisera raised against its native counterpart isolated from coffee beans and was biologically active towards the substrate p-nitrophenyl alpha-galactopyranoside. The subcellular distribution of recombinant alpha-galactosidase expressed from different vectors was analyzed by Western blotting, immunofluorescent labeling, and electron microscopy. In addition, recombinant alpha-galactosidase was compared to the native enzyme with respect to glycosylation, thermostability, and pH profile. Furthermore, a recombinant alpha-galactosidase molecule with a His6 tag at its C-terminus was constructed by an overlap PCR method so that the enzyme expressed in Sf9 cells can be purified by a simple affinity chromatography procedure.

Animals↗
PubMed1996

Expression, purification, and characterization of recombinant alpha-N-acetylgalactosaminidase produced in the yeast Pichia pastoris.

alpha-N-Acetylgalactosaminidase (alpha NAGAL, EC 3.2.1.49) purified from chicken liver has been used in seroconversion of human erythrocytes. Blood group A, defined by the terminal alpha-linked N-acetylgalactosamine, can be cleaved in vitro by alpha NAGAL, resulting in the underlying penultimate blood group H (O) epitope structure. In order to produce sufficient quantities of recombinant alpha NAGAL (r alpha NAGAL) for such studies, we expressed the cDNA encoding chicken liver alpha NAGAL in Pichia pastoris, a methylotrophic yeast strain. The alpha NAGAL coding sequence was cloned into the EcoRI site of the vector pPIC 9 such that the protein was in the same reading frame as the secretion signal of yeast alpha-mating factor derived from the vector. After P. pastoris transformation, colonies were screened for high-level expression of r alpha NAGAL based on enzyme activity. As a result of methanol induction of high-density cell cultures in a fermentor, enzymatically active r alpha NAGAL was produced and secreted into the culture medium. The recombinant enzyme was purified over 150-fold by chromatography on a cation exchange column followed by an affinity column. Its homogeneity was confirmed by Coomassie blue-stained SDS-PAGE, Western blot, and N-terminal sequencing. The purified r alpha NAGAL has a molecular mass of approximately 50 kDa while its native counterpart has a molecular mass of 43 kDa. This discrepancy in size was eliminated by endoglycosidase treatment, suggesting that the recombinant protein was hyperglycosylated by the host P. pastoris cells. r alpha NAGAL was further characterized in terms of specific activity, pH profile, kinetic parameters, and thermostability by comparing with alpha NAGAL purified from chicken liver. The data presented here suggest that by overexpressing r alpha NAGAL in P. pastoris and purifying with affinity chromatography one can readily obtain the quantity of enzyme needed for seroconversion studies.

Amino Acid Sequence↗
PubMed1995

Identification of tyrosine 108 in coffee bean alpha-galactosidase as an essential residue for the enzyme activity.

The cDNA for coffee bean alpha-galactosidase (alpha-Gal) has been cloned and expressed in a baculovirus expression system. An early study of coconut alpha-Gal by chemical modification suggested that one tyrosine residue is at or near the active site. In order to identify such a critical residue, we replaced two tyrosine residues (positions 108 and 158) with phenylalanine by site-directed mutagenesis. The mutated DNA strands, as well as the wild-type ones, were subcloned into pVL vector and transformed into Sf9 insect cells for intracellular expression. The replacement of Tyr-158 with phenylalanine resulted in a mutant alpha-Gal (Y158F) which retained approx. 88% of the activity of wild-type enzyme. However, the substitution of Tyr-108 by phenylalanine (Y108F) almost abolished the enzymatic activity (1.8% of wild-type activity). The Vmax/Km value for the mutant Y108F was 0.027, which was over a 1000-fold lower than that of wild-type alpha-Gal. Our data suggest that Tyr-108 is critical for the enzymatic activity of alpha-Gal.

Baculoviridae↗
PubMed1992

Maturation and fertilization of porcine oocytes in vitro.

Four experiments were conducted to study 1) factors affecting porcine oocyte maturation in culture medium and 2) a new method for oocyte maturation outside the porcine body. In Experiment 1, five groups of oocytes were cultured in m-TCM199 or m-KRB medium for 24 to 28, 32 to 36 or 40 to 42 hours and then were fertilized in vitro. The cleavage rate (two to four-cell stage) of oocytes cultured for 32 to 36 hours was significantly higher than those of the other oocytes. The results indicate that a suitable culture period for the in vitro maturation of porcine oocytes is 32 to 36 hours. In Experiment 2, four groups of oocytes were cultured in m-KRB or m-KRB supplemented with PFF, PMSG or FSH for in vitro maturation, and the cleavage rates of oocytes were 7.94, 22.56, 30.23 and 23.26%, respectively, after in vitro fertilization. The results show that porcine follicular fluid (PFF) and gonadotrophins added to the culture medium promote porcine oocyte maturation in vitro. In Experiment 3, oocytes were cultured in m-KRB or m-TCM199, supplemented with both gonadotrophin and pocine folliclar fluid for maturation in vitro. After fertilization in vitro, the cleavage rates of oocytes were 26.32 and 27.93% for the two media. The results indicate that the difference between m-KRB and m-TCM199 was insignificant when the media were used to culture porcine oocytes. But there was a significant difference when PFF and gonadotrophins were added to the basic media. In Experiment 4, porcine oocytes were transferred into the reproductive tracts of other animals for maturation. After 34 to 36 hours, the oocytes were collected and fertilized in vitro. The cleavage rates of oocytes were 10.42, 28.45, 3.33 and 36.36%, respectively, for the oocytes matured in mouse uterine horns, rat uterine horns, rat oviducts or rabbit oviducts. The results show that porcine oocytes can be matured in the reproductive tracts of other animals.

Journal Article↗