title: Monovalent Cation Activation of Plant Pyruvate Dehydrogenase Kinase.
abstract: 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.
authors.affiliation: Biochemistry Department, University of Missouri, Columbia, Missouri 65211.
authors.forename: K. A.
authors.initials: KA
authors.lastname: Schuller
authors.forename: J.
authors.initials: J
authors.lastname: Gemel
authors.forename: D. D.
authors.initials: DD
authors.lastname: Randall