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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 3
BKCSDE 26(3)
March 20, 2005 

Functional Studies of Tyrosine 108 Residue in the Active Site of Human Glutathione S-Transferase P1-1
Hee-Joong Park, Jong-Uk Koh, So-Youn Ahn, Kwang-Hoon Kong*
Tyrosinase 108 residue, Enzymatic properties, Glutathione S-transferase, Substrate specificity
To gain further insight on the relationship between structure and functions of glutathione S-transferase (GST), the three tyrosine 108 mutants, Y108A, Y108F, and Y108W, of human GST P1-1 were expressed in Escherichia coli and purified to electrophoretic homogeneity by affinity chromatography on immobilized GSH. The substitution of Tyr 108 with alanine resulted in significant decrease of the GSH-conjugation activity and the GSH peroxidase activity, but approximately 63% increase of steroid isomerase activity toward ?5? androstene 3,17-dione. On the other hand, the substitution of Tyr 108 with phenylalanine resulted in decreases of kcat and kcat/Km EPNP by 2 orders of magnitude, suggesting that Tyr 108 residue of hGSTP1-1 are considered to be important for the catalysis and the binding of the epoxide substrates. The substitution of Tyr 108 with tryptophan resulted in significant decreases of the specific activities toward EPNP, cumene hydroperoxide and ?5?androstene 3,17-dione, but approximately 2-fold increase on the enzyme-catalyzed addition of GSH to DCNB. We conclude from these results that Tyr 108 in hGST P1-1 plays very different roles depending upon the nature of the electrophilic substrates.
433 - 439
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