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Biomedical subjects

L J Chen

Publications and source records attributed to L J Chen.

At least 109 records · Page 6Linked to original sources
PubMed1978

Sex differences in hepatic sulfation of taurolithocholate in the rat.

Metabolism of the bile salts by formation of sulfate esters is catalyzed by bile salt sulfotransferase, an enzyme isolated from rat liver and kidney. The activity of bile salt sulfotransferase was measured in liver and kidney of male and female rats and in oophorectomized rats with or without estrogen replacement. In vitro sulfotransferase activity was correlated with in vivo sulfation by measuring the percentage of an infused dose (0.03 micron per 100 g per min) of taurolithocholate, which was excreted in bile as the sulfate. The activity of sulfotransferase in liver was higher in females (26.3 +/- 3.0 pmoles per mg of protein per min) than in males (9.6 +/- 3.9) and was lower (12.1 +/- 3.8) after oophorectomy. The decrease in activity was prevented by replacement of estrogen. Renal sulfotransferase activity did not differ between the sexes and was unaffected by oophorectomy. Hepatic sulfotransferase activity measured in vitro correlated with in vivo sulfation of taurolithocholate. This study shows definite sex differences in hepatic bile salt sulfotransferase activity, which in females is affected by the presence of estrogen. The correlation between in vitro sulfotransferase activity and in vivo bile salt sulfation suggests that bile salt sulfotransferase is responsible for bile salt sulfation in vivo.

Animals↗
PubMed1977

Enzymatic sulfation of bile salts. Partial purification and characterization of an enzyme from rat liver that catalyzes the sulfation of bile salts.

An enzyme system which catalyzes the transfer of sulfate group from 3'-phosphoadenosine-5'-phosphosulfate to bile salts has been identified and characterized from rat liver. The enzyme is present in the cytosol fraction of liver cells. The apparent Km value for 3'-phosphoadenosine-5'-phosphosulfate was 8 - 10(-6) M andhat for taurolithocholate was 5 - 10(-5) M. Sulfation occurred with conjugated as well as unconjugated bile salts, however, the rate of sulfation was higher with conjugated than unconjugated. The enzyme was present in rat liver and kidney, but not detectable in brain, lung, heart, spleen or intestinal mucosa. The activity is completely inhibited by p-chloromercuribenzoate indicating the enzyme requires a sulfhydryl group for activity. A molecular weight of 130 000 was estimated by gel-filtration technique and the enzyme shows an isoelectric point of 5.3.

Animals↗
PubMed1977

Hydrolysis of lithocholate sulfate by Pseudomonas aeruginosa.

Pseudomonas aeruginosa was found to be able to hydrolyze bile sulfate. This property was observed when lithocholate sulfate was substituted for the sulfur source in the culture medium. The addition of MgSO4 to the medium inhibited the hydrolysis of the bile sulfate.

Cholic Acids↗
PubMedDate not supplied

Regulation of bile salt sulfotransferase isoenzymes by gonadal hormones.

We studied the regulation of hepatic bile salt sulfotransferase activity by gonadal hormones and the effect of gonadal hormones on two bile salt sulfotransferase isoenzymes. Bile salt sulfotransferase enzyme activity was three times greater in the female than in the male rats. Oophorectomy significantly decreased bile salt sulfotransferase activity in the female, but orchidectomy had no effect on bile salt sulfotransferase activity in the male. Estrogen treatment of intact as well as orchidectomized males markedly stimulated the enzyme activity, while testosterone treatment of intact or oophorectomized females did not effect bile salt sulfotransferase activity. We concluded that the 3-fold greater activity in female rats is due to the striking stimulatory effect of estrogen on bile salt sulfotransferase activity, and the testosterone has little or no role in the sexually related differences in bile salt sulfotransferase activity in mature rats. These sex-related differences in bile salt sulfotransferase activity were investigated further using DEAE-Sephadex A50 ion-exchange chromatography of rat hepatic cytosol. Two bile salt sulfotransferase isoenzymes were identified both with an approximate molecular weight of 130,000. Bile salt sulfotransferase I eluted with 0.05 M NaCl, had an isoelectric point at pH 6.8, was stimulated by estrogen, and was responsible for 90% of total bile salt sulfotransferase activity in the mature female. Bile salt sulfotransferase II eluted with 0.14 M NaCl, had an isoelectric point at pH 5.3, was unresponsive to estrogen, and accounted for 75 to 80% of bile salt sulfotransferase activity in the mature male.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Preparation of antigastric cancer monoclonal antibody MGb2-mitomycin C conjugate with improved antitumor activity.

In the present study, an antigastric cancer monoclonal antibody, MGb2, was chosen to prepare antibody-mitomycin C conjugate with dextran T-40 as intermediary. Up to 20 molecules of mitomycin C were specifically bound per molecule of antibody, without significantly impairing the antigen-binding capacity of the antibody and the pharmacological activity of mitomycin C. The conjugate showed selective cytotoxicity upon human gastric cancer cell line SGC-7901 in vitro. Radioimmunoimaging and biodistribution studies indicated that, after conjugation with mitomycin C via dextran T-40 as intermediary, the tumor localization capacity of the antibody was well-retained. When tested in nude mice inoculated with human gastric carcinoma GAII in bilateral subrenal capsules, intraperitoneal injection of the conjugate twice a week for 3 weeks at the dose of 1 mg/kg of drug gave a tumor inhibitory rate of 152.29%, the result being far better than that of free mitomycin C or an irrelevant conjugate. A similar result was found in another nude mouse model of human gastric carcinoma SGC-7901. Meanwhile, after conjugation with antibody, the toxicity of mitomycin C on tested animals was significantly reduced.

Animals↗
PubMedDate not supplied

Improved adsorption to starch of a beta-galactosidase fusion protein containing the starch-binding domain from Aspergillus glucoamylase.

We have previously shown (Chen et al., 1991) that a beta-galactosidase (beta-gal) fusion protein (BSB133) containing 133 amino acids (aa) from the C-terminus of Aspergillus glucoamylase (GA) adsorbs strongly to starch compared to beta-gal, due to the presence of the GA starch-binding domain. We have now made deletions at the N-terminus of this 133-aa region to test the minimal size required for starch binding of beta-gal fusion proteins. Three fusion proteins (BSB119, BSB103, and BSB80) were genetically engineered, containing 119, 103, and 80 C-terminal aa from GA, respectively. The fusion proteins were expressed in Escherichia coli and purified. Purified BSB119 adsorbed to native starch at least 2-fold more strongly than did BSB133 or fusion proteins with shorter tails. Adsorption isotherms generated over a wide range of initial concentrations indicated a 10-fold difference in the loading capacity of starch for BSB119 (36.5 mg of protein/g of starch) compared to beta-gal (3.7 mg of protein/g of starch). Adsorption constants calculated from the initial slopes of the isotherms indicated a nearly 30-fold difference in affinity to starch for BSB119 (Kad = 63 mL/g of starch) compared to beta-gal (Kad = 2.3 mL/g of starch). BSB119 in the presence of crude enzyme extracts also bound to starch with a high affinity compared to a beta-gal control. Potential applications of the starch-binding tail include enzyme immobilization to starch or recovery and purification of target proteins from crude extracts.

Adsorption↗
PubMedDate not supplied

Identification of cis-2-butene-1,4-dial as a microsomal metabolite of furan.

The hepatocarcinogen furan is believed to be activated to the reactive aldehyde, cis-2-butene-1,4-dial, by microsomal enzymes. The rat liver microsomal metabolism of furan was examined in the presence of NADPH and semicarbazide. HPLC analysis of incubation mixtures revealed the formation of a metabolite that coeluted with standards for the bis-semicarbazone adduct of cis-2-butene-1,4-dial. The formation of this compound required the presence of NADPH, semicarbazide, and microsomes. Preparative isolation and chemical characterization of this metabolite confirmed the structural assignment. These data provide evidence that the reactive aldehyde, cis-2-butene-1,4-dial, is a major metabolic product of furan.

Aldehydes↗
PubMedDate not supplied

Manufacture and evaluation of bioactive and biodegradable materials and scaffolds for tissue engineering.

For tissue regeneration and tissue engineering applications, a number of bioactive and biodegradable composites, either porous or non-porous, were fabricated. The newly developed materials included tricalcium phosphate reinforced polyhydroxybutyrate and its copolymer, poorly crystallized hydroxyapatite reinforced chitin, and plasma sprayed hydroxyapatite reinforced poly(L-lactic acid). It was shown that these new materials could be successfully produced using the manufacturing techniques adopted. In vitro experiments revealed that the incorporation of bioceramic particles in biodegradable polymers rendered the composites bioactive and significantly improved the ability of composites to induce the formation of bone-like apatite on their surfaces. Degradation of composite scaffolds in simulated body fluid was observed and could be due to the simultaneous degradation of polymer matrix and dissolution of bioceramic particles.

Journal Article↗