Identification of Mu-Class Glutathione Transferases M2-2 and M3-3 as Cytosolic Prostaglandin E Synthases in the Human Brain
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- Beuckmann, C.T., Fujimori, K., Urade, Y. et al. Neurochem Res (2000) 25: 733. doi:10.1023/A:1007579507804
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Cytosolic prostaglandin (PG) E synthase was purified from human brain cortex. The N-terminal amino acid sequence, PMTLGYXNIRGL, was identical to that of the human mu-class glutathione transferase (GST) M2 subunit. Complementary DNAs for human GSTM2, GSTM3, and GSTM4 subunits were cloned, and recombinant proteins were expressed as homodimers in Escherichia coli. The recombinant GSTM2-2 and 3-3 catalyzed the conversion of PGH2 to PGE2 at the rates of 282 and 923 nmol/min/mg of protein, respectively, at the optimal pH of 8, whereas GSTM4-4 was inactive; although all three enzymes showed GST activity. The PGE synthase activity depended on thiols, such as glutathione, dithiothreitol, 2-mercaptoethanol, or L-cysteine. Michaelis-Menten constants and turnover numbers for PGH2 were 141 μM and 10.8 min−1 for GSTM2-2 and 1.5 mM and 130 min−1 for GSTM3-3, respectively. GSTM2-2 and 3-3 may play crucial roles in temperature regulation, nociception, and sleep-wake regulation by producing PGE2 in the brain.