TY - JOUR
T1 - Properties and reaction mechanism of C4 leaf pyruvate,Pi dikinase
AU - Jenkins, C. L.D.
AU - Hatch, M. D.
PY - 1985/5/15
Y1 - 1985/5/15
N2 - The properties and reaction mechanism of maize leaf pyruvate,Pi dikinase are described. Km values were determined for the forward reaction substrates, pyruvate, ATP, and Pi, at pH 7.4 and 8.0 and for reverse reaction substrates at pH 7.4. Enzyme activity was almost totally dependent on added monovalent cations in both directions. NH4+ was most effective, with Ka values of about 0.38 mm for the forward reaction and 2 mm for the reverse reaction. K+ also completely activated the enzyme in the forward direction (Ka = 8 mM) but only partially activated in the reverse direction. Na+ had little effect on either reaction. The pH optimum for the forward reaction was about 8.2; the reverse reaction optimum was about 6.9. Maximum activity for the reverse direction was about twice the maximum forward direction rate. From data on the requirements for the ATP-AMP exchange reaction, on the mechanism of inhibition of the forward reaction by PEP, AMP, and PPi and from the kinetics of the interaction of varying certain substrate pairs, it was concluded that the maize leaf pyruvate,Pi dikinase reaction proceeded by the two-step Bi Bi Uni Uni mechanism. This differs from the mechanism of catalysis by the bacterial enzyme.
AB - The properties and reaction mechanism of maize leaf pyruvate,Pi dikinase are described. Km values were determined for the forward reaction substrates, pyruvate, ATP, and Pi, at pH 7.4 and 8.0 and for reverse reaction substrates at pH 7.4. Enzyme activity was almost totally dependent on added monovalent cations in both directions. NH4+ was most effective, with Ka values of about 0.38 mm for the forward reaction and 2 mm for the reverse reaction. K+ also completely activated the enzyme in the forward direction (Ka = 8 mM) but only partially activated in the reverse direction. Na+ had little effect on either reaction. The pH optimum for the forward reaction was about 8.2; the reverse reaction optimum was about 6.9. Maximum activity for the reverse direction was about twice the maximum forward direction rate. From data on the requirements for the ATP-AMP exchange reaction, on the mechanism of inhibition of the forward reaction by PEP, AMP, and PPi and from the kinetics of the interaction of varying certain substrate pairs, it was concluded that the maize leaf pyruvate,Pi dikinase reaction proceeded by the two-step Bi Bi Uni Uni mechanism. This differs from the mechanism of catalysis by the bacterial enzyme.
UR - http://www.scopus.com/inward/record.url?scp=0022426133&partnerID=8YFLogxK
U2 - 10.1016/0003-9861(85)90811-2
DO - 10.1016/0003-9861(85)90811-2
M3 - Article
C2 - 2988448
AN - SCOPUS:0022426133
VL - 239
SP - 53
EP - 62
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
SN - 0003-9861
IS - 1
ER -