Biomedical subjects

D D Dao

Publications and source records attributed to D D Dao.

23 records · Page 2Linked to original sources

PubMed1981

Glutathione-mediated detoxification mechanisms of human placenta.

Glutathione peroxidase and GSH S-transferases play significant physiological roles in the detoxification mechanisms. The present study indicates that only selenium-dependent GSH-peroxidase I is present in human placenta. GSH-peroxidase II (non-selenium GSH-peroxidase) is totally absent from this tissue. The placental GSH-peroxidase has a relative molecular mass of 85 000 and is a tetramer of equal-size subunits. It is cyanide sensitive and its properties are similar to those of human erythrocyte GSH-peroxidase. In contrast to human liver, which has seven GSH S-transferases, the placenta has only one species of GSH S-transferase. This enzyme (pI 4.5, relative molecular mass 45 000, subunit size 22 500) has a different amino acid composition from that of liver and erythrocyte GSH S-transferases. From immunological studies, the placental GSH S-transferase appears also to have a genetic origin distinct from that of liver, erythrocyte and kidney GSH S-transferases. The placental GSH S-transferase does not express GSH-peroxidase activity. The overall substrate specificities of placental GSH S-transferase are also narrow, compared with liver enzymes. The present study indicates that, although these two GSH-linked detoxification mechanisms are operative in placenta, they appear to be less efficient than the similar mechanisms operating in liver.

Animals↗

PubMed1981

Enzymatic conjugation of erythrocyte glutathione with 1-chloro-2,4-dinitrobenzene: the fate of glutathione conjugate in erythrocytes and the effect of glutathione depletion on hemoglobin.

Erythrocyte glutathione (GSH) can be rapidly depleted by incubating the cells with 1-chloro-2,4-dinitrobenzene (CDNB), which forms 2,4-dinitrophenyl-S-glutathione with GSH through the reaction catalyzed by glutathione S-transferase. GSH-CDNB conjugate thus formed stays undegraded within the erythrocytes. This indicates that in the erythrocytes, mercapturic acid pathway is inoperative. Depletion of GSH in the intact erythrocytes by CDNB results in rapid oxidation of large amounts of hemoglobin to methemoglobin. When glutathione S-transferase-free hemolysate of erythrocytes is incubated with CDNB, the depletion of GSH as well as methemoglobin formation are minimal. Glutathione peroxidase and glutathione reductase activities of the erythrocytes are not affected by CDNB. These studies provide a specific enzymatic method for rapid removal of erythrocyte GSH and also indicate that GSH is vital in maintaining a reduced environment within the erythrocytes.

Chromatography, High Pressure Liquid↗

PubMed1980

Interrelationship between anionic and cationic forms of glutathione S-transferases of human liver.

Human liver glutathione S-transferases (GSH S-transferases) were fractionated into cationic and anionic proteins. During fractionation with (NH4)2SO4 the anionic GSH S-transferases are concentrated in the 65%-saturated-(NH4)2SO4 fraction, whereas the cationic GSH S-transferases separate in the 80%-saturated-(NH4)2SO4 fraction. From the 65%-saturated-(NH4)2SO4 fraction two new anionic GSH S-transferases, omega and psi, were purified to homogeneity by using ion-exchange chromatography on DEAE-cellulose, Sephadex G-200 gel filtration, affinity chromatography on GSH bound to epoxy-activated Sepharose and isoelectric focusing. By a similar procedure, cationic GSH S-transferases were purified from the 80%-saturated-(NH4)2SO4 fraction. Isoelectric points of GSH S-transferases omega and psi are 4.6 and 5.4 respectively. GSH S-transferase omega is the major anionic GSH S-transferase of human liver, whereas GSH S-transferase psi is present only in traces. The subunit mol.wt. of GSH S-transferase omega is about 22500, whereas that of cationic GSH S-transferases is about 24500. Kinetic and structural properties as well as the amino acid composition of GSH S-transferase omega are described. The antibodies raised against cationic GSH S-transferases cross-react with GSH S-transferase omega. There are significant differences between the catalytic properties of GSH S-transferase omega and the cationic GSH S-transferases. GSH peroxidase II activity is displayed by all five cationic GSH S-transferases, whereas both anionic GSH S-transferases do not display this activity.

Amino Acids↗

PubMed1979

Purification and properties of glutathione peroxidase from human placenta.

Glutathione peroxidase (glutathione--H2O2 oxidoreductase; EC 1.11.1.9) was purified to homogeneity from human placenta by using (NH4)2SO4 precipitation, ion-exchange chromatography, Sephadex gel filtration and preparative polyacrylamide-disc-gel electrophoresis. Glutathione peroxidase from human placenta is a tetramer, having 4g-atoms of selenium/mol of protein. The molecular weight of the enzyme is about 85000 with a subunit size of about 22,000. Kinetic properties of the enzyme are described. On incubation with cyanide, glutathione peroxidase is completely and irreversibly inactivated and selenium is released as a low-molecular-weight fragment. Reduced glutathione, beta-mercaptoethanol and dithiothreitol protect the enzyme from inactivation by cyanide and the release of selenium. Properties of human placental glutathione peroxidase are similar to those of isoenzyme A reported earlier by us from human erythrocytes. The presence of isoenzyme, B, reported earlier by us in human erythrocytes, was not detected in placenta. Also selenium-independent glutathione peroxidase (isoenzyme II), which is specific for cumene hydroperoxide, was not present in human placenta.

Chromatography, Gel↗

PubMedDate not supplied

Association between HLA-DQB1 and cervical dysplasia in Vietnamese women.

Host genetic background seems to play a key role in cervical carcinogenesis as only a small subset of women infected with high-risk human papillomaviruses (HPVs) develop cervical cancer. The rate of cervical cancer in Vietnamese women is notably high. To explore the association of human leukocyte antigen (HLA)-DQB1 alleles, HPV infection, and cervical dysplasia in this population, cervical smears were obtained from 101 women attending the obstetrics and gynecology clinic of Da Nang General Hospital in Vietnam. Besides the Papanicolaou test, HPV and HLA-DQB1 genotyping were performed using cervical smear DNA. Additionally, a subset of 30 blood samples was used as the gold standard for HLA genotyping. HLA-DQB1 alleles showed no association with HPV infection status. However, a positive association with cervical dysplasia was found for HLA-DQB1*0302 (P= 0.0229, relative risk (RR) = 4.737) and HLA-DQB1*0601 (P= 0.0370, RR = 4.038), whereas HLA-DQB1*0301 (P= 0.0152, RR = 0.221) was found negatively associated. The low diversity of HLA-DQB1 alleles, wide spectrum of HPV genotypes, and high prevalence of HPV 16 and HPV 18 observed in the study population suggest a permissive/susceptible genetic background that deserves further research. Total concordance of HLA-DQB1 genotyping results between blood and cervical cells confirms the potential value of cervical smears as an effective tool for the development of cervical cancer biomarkers.

Adult↗