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Plant Physiol, July 2000, Vol. 123, pp. 1077-1086
Alteration of the Adenine Nucleotide Response and Increased
Rubisco Activation Activity of Arabidopsis Rubisco Activase by
Site-Directed Mutagenesis1
Russell P.
Kallis,2
Robert G.
Ewy, and
Archie R.
Portis Jr.*
Department of Plant Biology, University of Illinois, Urbana,
Illinois 61801 (R.P.K., A.R.P.); and Photosynthesis Research Unit,
Agricultural Research Service, United States Department of Agriculture,
Urbana, Illinois 61801 (R.G.E., A.R.P.)
Arabidopsis Rubisco was activated in vitro at rates 2- to 3-fold
greater by recombinant Arabidopsis 43-kD Rubisco activase with the
amino acid replacements Q111E and Q111D in a phosphate-binding loop,
G-G-K-G-Q-G-K-S. However, these two mutant enzymes had only slightly
greater rates of ATP hydrolysis. Activities of the Q111D enzyme were
much less sensitive and those of Q111E were somewhat less sensitive to
inhibition by ADP. Both mutant enzymes exhibited higher Rubisco
activation activities over the physiological range of ADP to ATP
ratios. Enzymes with non-polar, polar, and basic residues substituted
at position Gln-111 exhibited rates of Rubisco activation less than the
wild-type enzyme. Estimates of the relative affinity of the wild type
and the Q111D, Q111E, and Q111S enzymes for adenosine nucleotides by a
variety of methods revealed that the nucleotide affinities were the
most diminished in the Q111D enzyme. The temperature stability of the
Q111D and Q111E enzymes did not differ markedly from that of the 43-kD
recombinant wild-type enzyme, which is somewhat thermolabile. The Q111D
and Q111E enzymes, expressed in planta, may provide a means to better
define the role of the ADP to ATP ratio in the regulation of Rubisco
activation and photosynthesis rate.
1
This work was supported in part by the Triagency
Program for Collaborative Research in Plant Biology (grant no. DOE
92ER20095) and by the U.S. Department of Energy (grant no. 97ER20268).
2
Present address: Department of Crop Sciences, 259 E.R.
Madigan Laboratory, 1201 W. Gregory Ave, Urbana, IL 61801.
*
Corresponding author; e-mail arportis{at}uiuc.edu; fax
217-244-4419.
© 2000 American Society of Plant Physiologists
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