PLANT PHYSIOLOGY , Vol 109, Issue 3 899-905, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Electron Transport Controls Glutamine Synthetase Activity in the Facultative Heterotrophic Cyanobacterium Synechocystis sp. PCC 6803
J. C. Reyes, J. L. Crespo, M. Garcia-Dominguez and F. J. Florencio
Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Sevilla-Consejo Superior de Investigaciones Cientificas, Apdo 1113, 41080 Sevilla, Spain
Glutamine synthetase (GS) from Synechocystis sp. PCC 6803 was inactivated
in vivo by transferring cells from light to darkness or by incubation with
the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea but
not with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone. Addition of
glucose prevented both dark and 3-(3,4-dichlorophenyl)-1,1-dimethylurea GS
inactivation. In a Synechocystis psbE-psbF mutant (T1297) lacking
photosystem II, glucose was required to maintain active GS, even in the
light. However, in nitrogen-starved T1297 cells the removal of glucose did
not affect GS activity. The fact that dark-inactivated GS was reactivated
in vitro by the same treatments that reactivate the ammonium-inactivated GS
points out that both nitrogen metabolism and redox state of the cells lead
to the same molecular regulatory mechanism in the control of GS activity.
Using GS antibodies we detected that dark-inactivated GS displayed a
different electrophoretic migration with respect to the active form in
nondenaturing polyacrylamide gel electrophoresis but not in sodium dodecyl
sulfate-polyacrylamide gel electrophoresis. The possible pathway to
modulate GS activity by the electron transport flow in Synechocystis cells
is discussed.
