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J. Biol. Chem., Vol. 282, Issue 9, 6053-6060, March 2, 2007

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Identification of Domains Involved in Tetramerization and Malate Inhibition of Maize C₄-NADP-Malic Enzyme^*

From the Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Universidad Nacional de Rosario, Suipacha 531, Rosario, Argentina

C₄ photosynthetic NADP-malic enzyme (ME) has evolved from non-C₄ isoforms and gained unique kinetic and structural properties during this process. To identify the domains responsible for the structural and kinetic differences between maize C₄ and non-C₄-NADP-ME several chimeras between these isoforms were constructed and analyzed. By using this approach, we found that the region flanked by amino acid residues 102 and 247 is critical for the tetrameric state of C₄-NADP-ME. In this way, the oligomerization strategy of these NADP-ME isoforms differs markedly from the one that present non-plant NADP-ME with known crystal structures. On the other hand, the region from residue 248 to the C-terminal end of the C₄ isoform is involved in the inhibition by high malate concentrations at pH 7.0. The inhibition pattern of the C₄-NADP-ME and some of the chimeras suggested an allosteric site responsible for such behavior. This pH-dependent inhibition could be important for regulation of the C₄ isoform in vivo, with the enzyme presenting maximum activity while photosynthesis is in progress.

Received for publication, October 5, 2006 , and in revised form, December 6, 2006.

^* This work was supported by Consejo Nacional de Investigaciones Científicasy Técnicas PIP number 3029, Agencia Nacional de Promoción Científica y Tecnológica PICT number 01-11604, and Fundación Antorchas Project N°4248-63. 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 Fellows of the Consejo Nacional de Investigaciones Científicas y Técnicas.

² Members of the Researcher Career of the Consejo Nacional de Investigaciones Científicas y Técnicas.

³ To whom correspondence should be addressed. Tel.: 54-341-4371955; Fax: 54-341-4370044; E-mail: candreo{at}fbioyf.unr.edu.ar.

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