title: Role of cardiac glutathione transferase and of the glutathione S-conjugate export system in biotransformation of 4-hydroxynonenal in the heart.
abstract: There is a remarkable difference in the isozyme pattern between cardiac and hepatic glutathione S-transferases in rat (Ishikawa, T., and Sies, H. (1984) FEBS Lett. 169, 156-160), and one near-neutral isozyme (pI = 6.9) of the cardiac glutathione S-transferases was found to have a significantly high activity toward 4-hydroxynonenal. The isozyme was inhibited by the resulting glutathione S-conjugate of 4-hydroxynonenal competitively with GSH and noncompetitively with 4-hydroxynonenal. The kinetic parameters estimated for the isozyme were: kcat = 460 mol X min-1 X mol enzyme-1, Km = 50 microM for 4-hydroxynonenal, Ki = 85 microM. When the heart was perfused with 4-hydroxynonenal, a marked decrease was observed in the intracellular GSH level, accompanied by an increase of glutathione S-conjugate of 4-hydroxynonenal in the heart. The rate of the conjugation reaction was more than 30 times the rate of the spontaneous reaction, the half-life of 4-hydroxynonenal in the heart being less than 4 s. The glutathione S-conjugate of 4-hydroxynonenal was released from the heart into the perfusion medium. Saturation kinetics were observed for the release with respect to the intracellular level of the S-conjugate (Vmax = 12 nmol X min-1 X g heart-1), and there was a competition by the S-conjugate for GSSG release. The release of the glutathione S-conjugate is considered as a carrier-mediated process and to be important not only in interorgan glutathione metabolism but also in diminishing the inhibitory effect of the S-conjugate on glutathione S-transferases and glutathione reductase.
mesh_terms: D000447:Aldehydes / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D003326:Coronary Circulation; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism / Q000502:physiology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008297:Male; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000447:Aldehydes; D007527:Isoenzymes; D005982:Glutathione Transferase; D005978:Glutathione; C027576:4-hydroxy-2-nonenal