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H Xia

Publications and source records attributed to H Xia.

126 records · Page 7Linked to original sources
PubMed1993

Replacement of the invariant tyrosine in the CAGY region of the human chorionic gonadotropin beta subunit.

The mammalian glycoprotein hormone beta subunits contain a highly conserved amino acid sequence, Cys-Ala-Gly-Tyr-Cys (residues 34-38 of human chorionic gonadotropin beta), that is denoted as the 'CAGY region'. Using site-directed mutagenesis we have replaced Tyr-37 in hCG beta, i.e., the invariant Tyr in all known mammalian CG, LH, FSH, and TSH beta subunits, with two hydrophobic amino acid residues, Phe and Leu. The resultant mutant forms were characterized for alpha subunit binding and the resulting heterodimers were analyzed for biological activity using two in vitro assays with transformed murine Leydig cells (MA-10). Chinese hamster ovary cells containing a stably integrated gene for bovine alpha were transiently transfected with a eukaryotic expression vector containing a Rous sarcoma viral promoter and the wild-type and mutant cDNAs. The hCG beta(Phe-37) mutant bound to alpha essentially to the same extent as hCG beta wild-type, while the hCG beta(Leu-37) mutant formed somewhat less heterodimer. The heterologous heterodimeric mutant and wild-type gonadotropins were equipotent in a competitive binding assay with [125I]hCG. In a steroidogenic assay, the mutant hormones were active, but they appeared slightly less potent than the wild-type form. Thus, this invariant Tyr can be replaced with another aromatic amino acid residue or with a hydrophobic, but not aromatic amino acid residue in hCG beta without any dramatic effect on function. These results indicate that Tyr-37 in hCG beta, while not obligatory, may participate, either directly or indirectly, in subunit assembly and that the hydroxyl group may function in a modulatory role in signaling.

Amino Acid Sequence↗
PubMed1993

Mutagenesis of the 'determinant loop' region of human choriogonadotropin beta.

The hormone-specific beta subunits of the four human glycoprotein hormones are homologous, and mapping studies are underway in many laboratories to delineate the amino acid residues responsible for receptor binding and activation. Results on the human choriogonadotropin beta (hCG beta) subunit, obtained using synthetic peptides, chemically modified derivatives, and mutant forms prepared via site-directed mutagenesis, have suggested that amino acid residues enclosed by the purported disulfide loop between Cys-93 and Cys-100 may contribute to receptor binding and perhaps specificity. Indeed, the 93-100 amino acid sequence is referred to as a determinant loop. We have used site-directed mutagenesis to prepare single amino acid residue replacements at positions not previously investigated in full length beta subunits; these include Arg-95, Ser-96, Thr-97, and Thr-98. In addition, Leu-92 was studied in an effort to determine whether changes immediately adjacent to the determinant loop alter receptor binding. The wild-type and mutant cDNAs for hCG beta were subcloned into a Prsv expression vector and transiently transfected into Chinese hamster ovary cells containing a stably integrated gene for bovine alpha. The concentrations of total expressed hCG beta in heterodimer form with the bovine alpha subunit were determined by radioimmunoassays. The mutant gonadotropins were assayed in vitro using a competitive binding assay with [125I]hCG and progesterone production, both in the transformed murine Leydig cell line, MA-10. Mutant beta subunits containing the replacements Lys-92, Ser-95, Asp-96, and Tyr-97 exhibited normal alpha subunit binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Lysine residues 2 and 104 of the human chorionic gonadotrophin beta subunit influence receptor binding.

Human chorionic gonadotrophin (hCG), like other members of the glycoprotein hormone family, contains a common alpha subunit and a hormone-specific beta subunit. The latter is a 145 amino acid residue polypeptide with six sites of glycosylation. Positions 2 and 104 are occupied by basic amino acid residues in the 12 known amino acid sequences of mammalian beta subunits from CG and LH, a related gonadotrophin that acts through the same receptor. Lysine residues are found in both these positions in hCG-beta. Using site-directed mutagenesis, each of these two lysines in hCG-beta was replaced with glutamic acid. The mutant and wild-type cDNAs were subcloned into a eukaryotic expression vector, which was then transiently transfected into Chinese hamster ovary cells containing a stably integrated gene for the bovine alpha subunit. Holoprotein formation occurred with each of the two heterologous gonadotrophin mutants, i.e. the bovine alpha subunit bound to hCG-beta (Glu2) and to hCG-beta (Glu104), as well as with the control, i.e. the bovine alpha subunit bound to the hCG-beta wild-type subunit. In two in-vitro assays, one a competitive binding assay with 125I-labelled hCG as bound ligand and the other based on stimulation of progesterone production in a transformed murine Leydig cell line, MA-10, both the heterodimers containing a mutant beta subunit exhibited bioactivity, but their potencies were lower than that of the bovine alpha subunit bound to the hCG-beta wild-type subunit. These results suggest that the basic amino acid residues at positions 2 and 104 in hCG-beta participate, either directly or indirectly, in receptor binding.

Amino Acid Sequence↗
PubMed1990

Developmental aspects of the sinus valves and the sinus venosus septum of the right atrium in human embryos.

In 32 human embryos from 5 to 27 mm of length, stages 13 to 23 (according to the Carnegie system of stages), the contributions of the sinus venosus septum and the right sinus valve of the right atrium to the formation of the Eustachian and Thebesian valve were examined by scanning electron microscopy. The sinus septum takes part in the subdivision of the right sinus valve into the Eustachian and the Thebesian valves. From its first origin the sinus septum forms a septal structure between the orifices of the right hepatic vein (hepatic portion of the inferior caval vein), the precursor of the inferior caval vein, and the left horn of the sinus venosus, the precursor of the coronary sinus. Before the incorporation of the sinus venosus into the right atrium, it has an intra-sinusal position, and extends between the bases of the left and the right sinus valve. During the incorporation of the sinus venosus into the right atrium the sinus septum receives an intra-atrial position, and its positional relationships to the sinus valves and the orifices of the corresponding veins remain unchanged in principle. Due to the connection between the sinus septum and the right sinus valve, after completion of the incorporation of the sinus, the superior portion of the right sinus valve branches y-like into a lateral limb, (i.e. its original inferior portion) and into a medial limb, (i.e. the sinus septum).(ABSTRACT TRUNCATED AT 250 WORDS)

Heart Septum↗
PubMed1990

[The augmenting effect of selenium(Se) on cell-mediated immunity. III. Se enhances delayed-type hypersensitivity reaction by promoting antigen presentation].

Delayed-type hypersensitivity reaction (DTH) to TNCB in TNCB-primed mice was increased when mice was treated with sodium selenite. In vitro studies showed that primed T cells proliferated more vigorously when TNP-conjugated spleen adherent cells (SAC) from Se-treated mice were the stimulators as compared with SAC of untreated controls. TNP-conjugated SAC treated in vitro with sodium selenite were even stronger stimulators than SAC treated in vitro. The results indicate that Se enhances DTH by promoting antigen presentation.

Animals↗
PubMedDate not supplied

Alterations in the biorheological features of some soft tissues after limb lengthening.

The aim of this study was to investigate the effects of a surgical limb lengthening procedure on the biorheological features of some lengthened soft tissues. In this procedure external fixators were applied to goats' right radius to stretch the tissues. The right forelegs of goats were lengthened by 2, 4 cm, respectively. After lengthening ceased, the goats were examined after different periods of time. The lengthened median nerves, arteries and veins were harvested and used to study their biorheological features. Tensile strength of lengthened and control specimens were measured and their stress relaxation features and stress-strain relationships were studied. Results showed that at the beginning of recovery, the stress-strain curves, relaxation curves and tensile strengths of the lengthened specimens began to deviate from those of their controls. However, with increasing recovery time, the curves and tensile strength of the lengthened specimens reverted to those of their controls. All the tissues studied exhibited the same behavior.

Animals↗
PubMedDate not supplied

Assessing environmental justice using Bayesian hierarchical models: two case studies.

Sound statistical methodology for assessing environmental justice is clearly needed, but has been slow to develop. In this paper, we investigate the use of hierarchical Bayesian methods for combining disparate sources of environmental data featuring complex correlations over both space and time. After a brief review of the Bayesian approach and its specific application to disease mapping problems, we illustrate two case studies. The first to these investigates the effect of a certain nuclear fuel reprocessing facility in Ohio on the lung cancer rates in the counties that surround it, while the second concerns the relation between air quality (especially in terms of ambient ozone levels) and pediatric emergency room visits due to asthma in the Atlanta metro area. We close by summarizing the method's implications for environmental justice, as well as future methodological and applied work.

Adult↗
PubMedDate not supplied

Extraction of pesticide residues in tea by water during the infusion process.

The extraction rate of pesticide residues in water during the infusion process is dependent on the water solubility. The extraction of pesticide residues by boiling water can be regarded as a reversible equilibrium between adsorption and dissolution. The influence of chemical degradation is not important. When the water solubility is lower than 5 mg/kg, the extraction rate is 1-4%. Within the water solubility range of 10-150 mg/kg the extraction rate (Ri) is very sensitive to the water solubility (S); the relationship can be described as Ri = 59.8log S-42.5. When water solubility is higher than 170 mg/kg, the extraction rate is 90-100%.

Pesticide Residues↗