PLANT PHYSIOLOGY , Vol 102, Issue 1 139-143, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Monovalent Cation Activation of Plant Pyruvate Dehydrogenase Kinase
K. A. Schuller, J. Gemel and D. D. Randall
Biochemistry Department, University of Missouri, Columbia, Missouri 65211
The pyruvate dehydrogenase kinase-catalyzed inactivation of the pyruvate
dehydrogenase complex was studied using dialyzed, soluble proteins from
mitochondria purified from green leaf tissue of Pisum sativum L. seedlings.
At subsaturating ATP concentrations, K+ or NH4+, but not Na+, stimulated
the pyruvate dehydrogenase kinase by lowering the Km(ATP). Micromolar
concentrations of NH4+ were required to produce the same effect as
millimolar concentrations of K+. This is apparent from the observations
that the activation constant (Kact) for NH4+ was 0.1 mM, whereas the
Kact(K+) was 0.7 mM. Maximal pyruvate dehydrogenase kinase velocities
attained with NH4+ were higher than those with K+, and, therefore, NH4+ was
able to stimulate PDH kinase further in the presence of saturating K+. This
result supports our conclusion that photorespiratory NH4+ production in
plant mitochondria may be involved in regulating the entry of carbon into
the Krebs cycle by way of the pyruvate dehydrogenase complex.
