Showing papers by "Xi Chen published in 1998"

Highly Efficient Chemoenzymatic Synthesis of α-Galactosyl Epitopes with a Recombinant α(1→3)-Galactosyltransferase

Abstract: α-Galactosyl epitopes are carbohydrate structures bearing a Galα1-3Galβ terminus. The interaction of these epitopes on the surface of animal cells with anti-α-galactosyl antibodies in human serum is believed to be the main cause in antibody-mediated hyperacute rejection in xenotransplantation. This report describes an efficient chemoenzymatic approach based on the use of recombinant α(1→3)-galactosyltransferase (α1,3-GalT) for the synthesis of xenoactive α-galactosyl epitopes, which are highly desired in the research of xenotransplantation and immunotherapy. A truncated bovine α1,3-GalT (80−368) was cloned into the pET15b vector and subsequently transformed into E. coli BL21 strain. This expression system efficiently produced the soluble recombinant enzyme on a large scale with highly specific activity. A variety of α(1→3)-galactosylated epitopes were synthesized using such a recombinant enzyme. In a unique fashion, α-galactosyl pentasaccharide was synthesized via a one-pot, two-step enzymatic synthesis w...

Cloning and expression of rat lung acidic Ca2+-independent PLA2 and its organ distribution

Abstract: A clone for a rat acidic Ca2+-independent phospholipase A2(aiPLA2) was isolated from a cDNA library prepared from rat granular pneumocytes with a probe based on the human aiPLA2 sequence (T. S. Kim...

Corrosion of Iron in Acid Solutions with Hydrogen Sulfide

Abstract: The influence of pH and the concentration of hydrogen sulfide (H2S) on corrosion of iron in acid solutions was studied using a potentiostatic polarization method. The alternating current (AC) impedance technique also was used to characterize the active dissolution process of iron. Results showed the dissolution process was accelerated by H2S. The anodic dissolution current (ia) increased with pH and H2S concentration with reaction orders of about npH = nH2S = 0.25 when the ratio of H2S concentration and hydrogen ion (H3O+) concentration was 101.5. The Nyquist diagram corresponding to the active dissolution process in the Tafel range exhibited two capacitive loops in addition to the well-known, high-frequency capacitive loop. A mechanism was proposed to explain the results in which H2S chemisorbed first on the electrode surface and then catalyzed the anodic dissolution of iron in two discharging steps.

Characterization of acidic ca2+ -independent phospholipase a2 of bovine lung

Abstract: An acidic Ca2+-independent phospholipase A2 (aiPLA2) has been isolated previously from rat lung and a human cDNA has been described. This study applied the method to larger scale isolation of the native protein from the bovine lung. A polyclonal antibody was generated to a 15 amino acid synthetic peptide based on a conserved rat/human sequence. This antibody recognized a single protein band with an estimated molecular mass of ≈29 kDa in a soluble fraction obtained from bovine lung homogenate. A 29 kDa protein that reacted with the aiPLA2 antipeptide antibody was detected in fractions containing aiPLA2 activity on sequential column chromatographies. The partially purified enzyme showed 176-fold increase over the homogenate in Ca2+-independent PLA2 activity at pH 4. Activity was maximal with phosphatidylcholine substrate and was significantly less with phosphatidylethanolamine and anionic phospholipids. The enzyme had no acyl group preference in phosphatidylcholine and showed no preference for oxidized substrate, but activity was less with 1-O-alkyl phosphatidylcholine. aiPLA2 activity was inhibited by a transition state phospholipid analog (MJ33, 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol), serine protease inhibitors, and the anti-peptide antibody but was insensitive to arachidonoyl trifluoromethyl ketone, bromoenol lactone, p-bromophenacyl bromide, and ATP. Analysis of N-terminal amino acid sequence for the 29 kDa protein demonstrated its high homology to human 26 kDa aiPLA2. These was no significant change in molecular mass of the protein following treatment with endoglycosidase F. Western blot of subcellular fractions from rat lung indicated aiPLA2 immunoreactivity with lamellar body, lysosomal, and cytosolic fractions. These results indicate isolation from bovine lung of a 29 kDa acidic Ca2+-independent phospholipase A2 homologue of the rat and human enzyme and provide evidence for specificity in the metabolism of lung surfactant phosphatidylcholine.

Highly Efficient Chemoenzymatic Synthesis of α-Galactosyl Epitopes with a Recombinant α(1→3)-Galactosyltransferase.

Abstract: α-Galactosyl epitopes are carbohydrate structures bearing a Galα1-3Galβ terminus. The interaction of these epitopes on the surface of animal cells with anti-α-galactosyl antibodies in human serum is believed to be the main cause in antibody-mediated hyperacute rejection in xenotransplantation. This report describes an efficient chemoenzymatic approach based on the use of recombinant α(1→3)-galactosyltransferase (α1,3-GalT) for the synthesis of xenoactive α-galactosyl epitopes, which are highly desired in the research of xenotransplantation and immunotherapy. A truncated bovine α1,3-GalT (80−368) was cloned into the pET15b vector and subsequently transformed into E. coli BL21 strain. This expression system efficiently produced the soluble recombinant enzyme on a large scale with highly specific activity. A variety of α(1→3)-galactosylated epitopes were synthesized using such a recombinant enzyme. In a unique fashion, α-galactosyl pentasaccharide was synthesized via a one-pot, two-step enzymatic synthesis w...