
TY  - JOUR
A1  - Hatch, MD 
T1  - Regulation of C<sub>4</sub> Photosynthesis: Factors Affecting Cold-Mediated Inactivation and Reactivation of Pyruvate, P<sub>I</sub> Dikinase
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1979
VL  - 6
IS  - 6
SP  - 607
EP  - 619
KW  - 
UR  - https://doi.org/10.1071/PP9790607 
N2  - The kinetics and other characteristics of cold-induced inactivation and subsequent reactivation of pyruvate, PI dikinase from Zea mays were examined in leaf extracts and with the partially purified enzyme. Significant inactivation occurred at about 10&#176;C and the rate of inactivation increased as the temperature was reduced below 10&#176;C. The rate of inactivation at 0&#176;C varied with Mg2+ concentration; the half-time for inactivation was about 5 min with 2 mM Mg2+ compared with more than 60 min with 15 mM Mg2+. With 10 mM Mg2+, used routinely, the half-time for pyruvate,P*i dikinase isolated from a variety of species varied from less than 10 min to more than 40 min. Activity was rapidly recovered by rewarming to 25&#176;C the kinetics of reactivation were second order. Cold-induced inactivation was completely prevented by both pyruvate and phosphoenolpyruvate at concentrations of about 2 mM and 0.1 mM, respectively. The molecular weight of cold-inactivated pyruvate,PI dikinase, assessed by mobility on Sepharose 6B, was about a quarter of the active enzyme; the tetrameric active enzyme apparently dissociates to monomers at 0&#176;C. When illuminated leaves were exposed to lower temperature, pyruvate, Pi dikinase was partially inactivated. This activity was rapidly recovered by returning leaves to a temperature of 25&#176;C, or by incubating extracts from the cold-treated leaves at 25&#176;C. The dark-inactivated enzyme was apparently also modified by exposure to temperatures in the range 0-5&#176;C. 
ER  -

