Can glutathione-S-transferases function as intracellular heme carriers?
The possibility that glutathione-S-transferases can serve as heme carriers in cells was studied via the following two characteristics: the ability to bind hemin reversibly and the coordination between heme and glutathione-S-transferases level in the cell. two erythroleukemic cell lines that can be induced to synthesize hemoglobin were studied, K-562 and Friend murine erythroleukemia cells. It was found that hemin-associated glutathione-S-transferase tends to lose its native structure as expressed by partial irreversible inhibition of glutathione conjugation activity. In K-562 cells, a small increase in heme synthesis was induced, but under no condition could glutathione-S-transferase be elevated. In addition, introduction of high hemin from without caused large hemoglobin production but did not induce changes in the glutathione-S-transferase content. Dimethyl sulfoxide-induced Friend murine erythroleukemia cells synthesized a large amount of endogenous hemin that had to be transported from the mitochondria for hemoglobin synthesis. Although a concomitant increase in glutathione-S-transferase level (20-40%) was observed, it was only short-lived, unlike hemin, which continued to increase. These data indicate a lack of correlation between glutathione-S-transferase and hemin or hemoglobin levels. Finally, dimethyl sulfoxide-induced cells were treated with succinyl acetone to inhibit heme synthesis. These cells showed the same increased levels and time-dependent pattern of glutathione-S-transferase as untreated cells. A similar phenomenon was observed when different substrates were used to measure the activities of glutathione-S-transferases. These results raise doubts about the possibility of glutathione-S-transferases functioning as heme carriers in cells.
Kirschner-Zilber
I
I
Sackler Institute of Molecular Medicine, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Laufer
H
H
Shaklai
N
N
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002352:Carrier Proteins; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D005914:Globins / Q000378:metabolism / Q000494:pharmacology; D005982:Glutathione Transferase / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D006418:Heme / Q000031:analogs & derivatives*; D006427:Hemin / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism; D051379:Mice; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism
D002352:Carrier Proteins; D006418:Heme; D006427:Hemin; D005914:Globins; D005982:Glutathione Transferase; D004121:Dimethyl Sulfoxide