Poster: Enzymology

Abs # 239: Investigation of the cofactor cospecificity of formate dehydrogenase in Arabidopsis thaliana

Presenter:	Baack, Renee D., rbaack1@yahoo.com
Authors	Baack, Renee D. (A)   Herman, Patricia L. (B)   Osterman, John C. (B)   Beavers, Kevin A. (B)   Markwell, John  (A)
Affiliations:	(A): Dept. Biochem., Univ. Nebraska (B): Sch. Biol. Sci., Univ. Nebraska

Formate dehydrogenase is a NAD-specific mitochondrial enzyme that catalyzes the oxidation of formate to carbon dioxide. It has recently been reported by our laboratory that this enzyme is also localized in chloroplasts in Arabidopsis and that the kinetic properties of the enzyme in its native state differ significantly from those of the purified enzyme. The Km differences of the two enzymes can be mimicked by heating the native enzyme to 60 C for five minutes, causing a decrease in the Km for formate and NAD⁺. Heating seems to convert this metastable enzyme to a molten form that can then refold into an alternate conformation upon cooling. We now report this alternate conformation also possesses the ability to use either NAD or NADP as a substrate for the oxidation of formate. Such cospecificity has been engineered previously into the yeast enzyme, but is thus far unique for the formate dehydrogenases of higher plants. The possibility of engineering a chloroplastic formate dehydrogenase able to use NADPH as a reductant raises some interesting physiological possibilities.