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J. Biol. Chem., Vol. 282, Issue 3, 1561-1569, January 19, 2007

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Thioredoxin-dependent Enzymatic Activation of Mercaptopyruvate Sulfurtransferase

AN INTERSUBUNIT DISULFIDE BOND SERVES AS A REDOX SWITCH FOR ACTIVATION^*

Noriyuki Nagahara¹, Taro Yoshii, Yasuko Abe, and Tomohiro Matsumura

From the Department of Environmental Medicine and the Department of Biochemistry and Molecular Biology, Nippon Medical School, Tokyo 113-8602, Japan

Rat 3-mercaptopyruvate sulfurtransferase (MST) contains three exposed cysteines as follows: a catalytic site cysteine, Cys²⁴⁷, in the active site and Cys¹⁵⁴ and Cys²⁶³ on the surface of MST. The corresponding cysteine to Cys²⁶³ is conserved in mammalian MSTs, and Cys¹⁵⁴ is a unique cysteine. MST has monomer-dimer equilibrium with the assistance of oxidants and reductants. The monomer to dimer ratio is maintained at 92:8 in 0.2 M potassium phosphate buffer containing no reductants under air-saturated conditions; the dimer might be symmetrical via an intersubunit disulfide bond between Cys¹⁵⁴ and Cys¹⁵⁴ and between Cys²⁶³ and Cys²⁶³, or asymmetrical via an intersubunit disulfide bond between Cys¹⁵⁴ and Cys²⁶³. Escherichia coli reduced thioredoxin (Trx) cleaved the intersubunit disulfide bond to activate MST to 2.3- and 4.9-fold the levels of activation of dithiothreitol (DTT)-treated and DTT-untreated MST, respectively. Rat Trx also activated MST. On the other hand, reduced glutathione did not affect MST activity. E. coli C35S Trx, in which Cys³⁵ was replaced with Ser, formed some adducts with MST and activated MST after treatment with DTT. Thus, Cys³² of E. coli Trx reacted with the redox-active cysteines, Cys¹⁵⁴ and Cys²⁶³, by forming an intersubunit disulfide bond and a sulfenyl Cys²⁴⁷. A consecutively formed disulfide bond between Trx and MST must be cleaved for the activation. E. coli C32S Trx, however, did not activate MST. Reduced Trx turns on a redox switch for the enzymatic activation of MST, which contributes to the maintenance of cellular redox homeostasis.

Received for publication, June 21, 2006 , and in revised form, November 13, 2006.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Environmental Medicine, Nippon Medical School, 1-1-5 Sendagi Bunkyo-ku, Tokyo 113-8602, Japan. Tel.: 81-3-3822-2131; Fax: 81-3-5685-3065; E-mail: noriyuki{at}nms.ac.jp.

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