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J. Biol. Chem., Vol. 278, Issue 28, 25628-25636, July 11, 2003

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Physical and Genetic Interactions of Cytosolic Malate Dehydrogenase with Other Gluconeogenic Enzymes^*

Natalie Gibson and Lee McAlister-Henn 

From the Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900

A truncated form (nMDH2) of yeast cytosolic malate dehydrogenase (MDH2) lacking 12 residues on the amino terminus was found to be inadequate for gluconeogenic function in vivo because the mutant enzyme fails to restore growth of a mdh2 strain on minimal medium with ethanol or acetate as the carbon source. The nMDH2 enzyme was also previously found to be refractory to the rapid glucose-induced inactivation and degradation observed for authentic MDH2. In contrast, kinetic properties measured for purified forms of MDH2 and nMDH2 enzymes are very similar. Yeast two-hybrid assays indicate weak interactions between MDH2 and yeast phosphoenolpyruvate carboxykinase (PCK1) and between MDH2 and fructose-1,6-bisphosphatase (FBP1). These interactions are not observed for nMDH2, suggesting that differences in cellular function between authentic and truncated forms of MDH2 may be related to their ability to interact with other gluconeogenic enzymes. Additional evidence was obtained for interaction of MDH2 with PCK1 using Hummel-Dreyer gel filtration chromatography, and for interactions of MDH2 with PCK1 and with FBP1 using surface plasmon resonance. Experiments with the latter technique demonstrated a much lower affinity for interaction of nMDH2 with PCK1 and no interaction between nMDH2 and FBP1. These results suggest that the interactions of MDH2 with other gluconeogenic enzymes are dependent on the amino terminus of the enzyme, and that these interactions are important for gluconeogenic function in vivo.

Received for publication, December 27, 2002 , and in revised form, April 1, 2003.

^* This work was supported by National Science Foundation Grant MCB-9816774 and National Institutes of Health Grant 1S10RR15883. 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 should be addressed. Tel.: 210-567-3782; Fax: 210-567-6595; E-mail: henn{at}uthscsa.edu.

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