PLANT PHYSIOLOGY , Vol 108, Issue 1 69-73, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Fructose-1,6-Bisphosphate Is an Allosteric Activator of Pyrophosphate:Fructose-6-Phosphate 1-Phosphotransferase
T. H. Nielsen
Department of Plant Biology, Plant Biochemistry Laboratory, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark
The activity of highly purified pyrophosphate:fructose-6-phosphate
1-phosphotransferase (PFP) from barley (Hordeum vulgare) leaves was studied
under conditions where the catalyzed reaction was allowed to approach
equilibrium. The activity of PFP was monitored by determining the changes
in the levels of fructose-6-phosphate, orthophosphate, and
fructose-1,6-bisphosphate (Fru-1,6-bisP). Under these conditions PFP
activity was not dependent on activation by fructose-2,6-bisphosphate
(Fru-2,6-bisP). Inclusion of aldolase in the reaction mixture temporarily
restored the dependence of PFP on Fru-2,6-bisP. Alternatively, PFP was
activated by Fru-1,6-bisP in the presence of aldolase. It is concluded that
Fru-1,6-bisP is an allosteric activator of barley PFP, which can substitute
for Fru-2,6-bisP as an activator. A significant activation was observed at
a concentration of 5 to 25 [mu]M Fru-1,6-bisP, which demonstrates that the
allosteric site of barley PFP has a very high affinity for Fru-1,6-bisP.
The high affinity for Fru-1,6-bisP at the allosteric site suggests that the
observed activation of PFP by Fru-1,6-bisP constitutes a previously
unrecognized in vivo regulation mechanism.
