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J. Biol. Chem., Vol. 280, Issue 7, 5486-5490, February 18, 2005

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Regulation of Aldoxime Dehydratase Activity by Redox-dependent Change in the Coordination Structure of the Aldoxime-Heme Complex^*

Katsuaki Kobayashi, Shiro Yoshioka, Yasuo Kato, Yasuhisa Asano¶, and Shigetoshi Aono||

From the Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan and the Biotechnology Research Center, Faculty of Engineering, Toyama Prefectural University, 5180 Kurokawa, Kosugi, Toyama 939-0398, Japan

Phenylacetaldoxime dehydratase from Bacillus sp. strain OxB-1 (OxdB) catalyzes the dehydration of Z-phenylacetaldoxime (PAOx) to produce phenylacetonitrile. OxdB contains a protoheme that works as the active center of the dehydration reaction. The enzymatic activity of ferrous OxdB was 1150-fold higher than that of ferric OxdB, indicating that the ferrous heme was the active state in OxdB catalysis. Although ferric OxdB was inactive, the substrate was bound to the ferric heme iron. Electron paramagnetic resonance spectroscopy revealed that the oxygen atom of PAOx was bound to the ferric heme, whereas PAOx was bound to the ferrous heme in OxdB via the nitrogen atom of PAOx. These results show a novel mechanism by which the activity of a heme enzyme is regulated; that is, the oxidation state of the heme controls the coordination structure of a substrate-heme complex, which regulates enzymatic activity. Rapid scanning spectroscopy using stopped-flow apparatus revealed that a reaction intermediate (the PAOx-ferrous OxdB complex) showed Soret, , and bands at 415, 555, and 524 nm, respectively. The formation of this intermediate complex was very fast, finishing within the dead time of the stopped-flow mixer (3 ms). Site-directed mutagenesis revealed that His-306 was the catalytic residue responsible for assisting the elimination of the hydrogen atom of PAOx. The pH dependence of OxdB activity suggested that another amino acid residue that assists the elimination of the OH group of PAOx would work as a catalytic residue along with His-306.

Received for publication, September 13, 2004 , and in revised form, November 23, 2004.

^* This work was supported in part by a Grant-in-aid for Scientific Research into Priority Areas in Metal Sensors (12147203 to S. A.) from the Ministry of Education, Culture, Sports, Science, and Technology in Japan and by a Grant-in-aid for Scientific Research B (16370065 to S. A.) from the Japan Society for the Promotion of Science. 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.

^¶ To whom correspondence may be addressed. Tel.: 81-766-56-7500 (ext. 530); Fax: 81-766-56-2498; E-mail: asano{at}pu-toyama.ac.jp. || To whom correspondence may be addressed. Tel.: 81-564-59-5575; Fax: 81-564-59-5576; E-mail: aono{at}ims.ac.jp.

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