|show drug details|
|Caswell No. 389C|
|EPA Pesticide Chemical Code 055102|
|WLN: WNR BG ENW|
|Ki: ||Kd:||Ic 50:||Ec50/Ic50:|
Human placental glutathione transferase: interactions with steroids.. L Dibbelt; C Schulte-Uebbing; E Kuss (1988) Biological chemistry Hoppe-Seyler display abstract
Glutathione transferases exhibit both isomerase and transferase activity. The acceptance of steroids as substrates for or inhibitors of these activities was studied using a 350-fold enriched preparation of the enzyme from human placenta. As an isomerase, the enzyme preparation catalyzed the conversion of pregn-5-ene-3,20-dione (Km 0.03 mmol/l) and androst-5-ene-3,17-dione (Km 0.05 mmol/l) to the respective 4-ene-3-oxosteroids (specific activity 0.8 U/mg protein). This isomerase activity strictly depended on the presence of glutathione (Km 0.04 mmol/l). As a transferase, the enzyme preparation catalyzed the conjugation of glutathione (Km 0.5 mmol/l) with 1-chloro-2,4-dinitrobenzene (Km 1.0 mmol/l) (specific activity 100 U/mg protein). This transferase activity was inhibited by all phenolic (KI values 0.2-1.5 mmol/l) and some of the neutral steroids (KI values 1.4-3.5 mmol/l) tested. Phenolic steroids inhibited the enzyme activity competitively to 1-chloro-2,4-dinitrobenzene and non-competitively to both substrates. The results indicate that steroids can interact with the placental glutathione transferase in vitro both as substrates and as inhibitors. Since, however, the observed Km and KI values of the steroids are far above the values of their concentrations in the placenta, these interactions are of only minor physiological relevance.
Glutathione-conjugate transport by human colon adenocarcinoma cells (Caco-2 cells).. R P Oude Elferink; C T Bakker; P L Jansen (1993) The Biochemical journal display abstract
The secretion of a glutathione-S-conjugate, dinitrophenyl-glutathione (GS-DNP) was studied in the Caco-2 cells, a cultured human colonic adenocarcinoma cell line with many of the characteristics of enterocytes. The labelled glutathione conjugate was generated within the cell by incubation with 14C-labelled 1-chloro-2,4-dinitrobenzene (CDNB). This compound is hydrophobic and enters the cell by simple diffusion. Cells incubated with CDNB at 10 degrees C form only one metabolite, GS-DNP. After secretion into the medium GS-DNP is partly converted into one or two slightly more hydrophobic products. This must represent hydrolysis of the glutathione moiety by the action of gamma-glutamyltransferase (EC 184.108.40.206.; gamma-GT) because the reaction was completely inhibited by acivicin, an inhibitor of gamma-GT. Secretion of GS-DNP was a temperature-sensitive, saturable process with an apparent Km of 1.03 +/- 0.26 nmol/mg of protein and a Vmax of 111 +/- 17 pmol/min per mg of protein. The secretion was not sensitive to trans-stimulation by extracellular concentrations of GS-DNP up to 2.5 mM. Furthermore the initial GS-DNP secretion rate was sensitive to dissipation of the membrane potential and correlated closely with the cellular ATP content. Caco-2 cells cultured on nitrocellulose filters secreted GS-DNP significantly faster over the basolateral membrane than over the apical membrane (146 +/- 25 versus 90 +/- 18 pmol/min per mg respectively). Secretion over both membrane domains of the cell was sensitive to ATP depletion. In conclusion, Caco-2 cells contain an active-transport system that is primarily involved in the secretion of glutathione conjugates and that is present in both plasma membrane domains of the cell.
Isoenzyme selective irreversible inhibition of rat and human glutathione S-transferases by ethacrynic acid and two brominated derivatives.. J H Ploemen; J J Bogaards; G A Veldink; B van Ommen; D H Jansen; P J van Bladeren (1993) Biochemical pharmacology display abstract
In the present study it has been shown that ethacrynic acid can inhibit glutathione S-transferase (GST) of the pi-class irreversibly. [14C]Ethacrynic acid, 0.8 nmol/nmol human P1-1 and 0.8 nmol/nmol rat GST 7-7 could be incorporated, resulting in 65-93% inhibition of the activity towards 1-chloro-2,4-dinitrobenzene (CDNB). Isoenzymes of the alpha- and mu-class also bound [14C]ethacrynic acid, however without loss of catalytic activity. Incorporation ranged from 0.3 to 0.6 and 0.2 nmol/nmol enzyme for the mu- and alpha-class GST isoenzymes, respectively. For all isoenzymes, incorporation of [14C]ethacrynic acid could be prevented by preincubation with tetrachloro-1,4-benzoquinone, suggesting, that a cysteine residue is the target site. Protection of GST P1-1 against inhibition by ethacrynic acid by the substrate analog S-hexylglutathione, indicates an active site-directed modification. The monobromo and dibromo dihydro derivatives of ethacrynic acid were synthesized in an effort to produce more reactive compounds. The monobromo derivative did not exhibit enhanced irreversible inhibitory capacity. However, the dibromo dihydro derivative inhibited both human and rat GST isoenzymes of the pi-class very efficiently, resulting in 90-96% inhibition of the activity towards CDNB. Interestingly, this compound is also a powerful irreversible inhibitor of the mu-class GST isoenzymes, resulting in 52-70% inhibition. The two bromine atoms only marginally affect the strong (reversible) competitive inhibitory capacity of ethacrynic acid, with IC50 (microM) of 0.4-0.6 and 4.6-10 for the mu- and pi-class GST isoenzymes, respectively.