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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 28, Number 2
BKCSDE 28(2)
February 20, 2007 

An Essential Histidine Residue in the Catalytic Mechanism of the Rat Kidney γ -Glutamyl Transpeptidase
Soo-Ja Kim, Moon Kyu Ko, Kyu-Yun Chai, Seong-Wan Cho, Woo-Yiel Lee*
Gamma-glutamyl transpeptidase, Essential histidine, Kinetic study, Chemical modification, Photooxidation
γ -Glutamyl transpeptidase (EC plays a key role in glutathione metabolism by catalyzing the transfer of the γ -glutamyl residue and hydrolysis of glutathione. The functional residues at the active site of the rat kidney γ -glutamyl transpeptidase were investigated by kinetic studies at various pH, the treatment of diethylpyrocarbonate (DEPC), and photooxidation in presence of methylene blue. An ionizable group affecting the enzymatic activity with an apparent pKa value of 7.1, which is in the range of pKa values for a histidine residue in protein, was obtained by examining the pH-dependence of kinetic parameters. The pH effect on the photoinduced inactivation rate of the enzyme corresponds to that expected for the photooxidation of the free histidine. The involvement of a histidine in the catalytic site of the enzyme was further supported by DEPC modification accompanied by an increase in absorbance at 240 nm, indicating the formation of Ncarbethoxyhistidine. The histidine located at the position of 382 in the precursor of the enzyme is primarily suspected based on the amino acid sequence alignment of the transpeptidases from various organisms.
271 - 275
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