Abstract
The inhibition patterns of inorganic phosphate (Pi) on sucrose phosphate synthase activity in the presence and absence of the allosteric activator glucose-6-P was studied, as well as the effects of phosphoglucoisomerase on fructose-6-P saturation kinetics with and without Pi. In the presence of 5 millimolar glucose-6-P, Pi was a partial competitive inhibitor with respect to both substrates, fructose-6-P and uridine diphosphate glucose. In the absence of glucose-6-P, the inhibition patterns were more complex, apparently because of the interaction of Pi at the activation site as well as the catalytic site. In addition, substrate activation by uridine diphosphate glucose was observed in the absence of effectors. The results suggested that Pi antagonizes glucose-6-P activation of sucrose phosphate synthase by competing with the activator for binding to the modifier site.The fructose-6-P saturation kinetics were hyperbolic in the absence of phosphoglucoisomerase activity, but became sigmoidal by the addition of excess phosphoglucoisomerase. The sigmoidicity persisted in the presence of Pi, but sucrose phosphate synthase activity was decreased. The apparent sigmoidal response may represent the physiological response of sucrose phosphate synthase to a change in hexose-P concentration because sucrose phosphate synthase operates in the cytosol in the presence of high activities of phosphoglucoisomerase. Thus, the enzymic production of an activator from a substrate represents a unique mechanism for generating sigmoidal enzyme kinetics.
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Claims 9
Claim · model-written summary
With glucose-6-P, phosphate partially competitively inhibited sucrose phosphate synthase against two substrates.
- Taxon
- Spinach
Spinacia oleraceat0 - Treatment
- Pie0
- Gene
- Sucrose Phosphate Synthaset0
- Compound
- glucose-6-Pe0
- Outcome
- Sucrose Phosphate Synthaset0
- Direction
- inhibitore0
- Qualifier
- fructose-6-P and uridine diphosphate glucosee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the presence of 5 millimolar glucose-6-P, Pi was a partial competitive inhibitor with respect to both substrates, fructose-6-P and uridine diphosphate glucose.”
t0“Spinach Leaf Sucrose Phosphate Synthase”
Claim · model-written summary
Without glucose-6-P, phosphate inhibition patterns were more complex.
- Taxon
- SpinachSpinacia oleraceat0
- Gene
- Sucrose Phosphate Synthaset0
- Outcome
- inhibition patternse0
- Direction
- more complexe0
- Qualifier
- absence of glucose-6-Pe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the absence of glucose-6-P, the inhibition patterns were more complex, apparently because of the interaction of Pi at the activation site as well as the catalytic site.”
t0“Spinach Leaf Sucrose Phosphate Synthase”
Claim · model-written summary
Uridine diphosphate glucose activated the enzyme without effectors.
- Taxon
- SpinachSpinacia oleraceat0
- Compound
- uridine diphosphate glucosee0
- Outcome
- substrate activatione0
- Qualifier
- absence of effectorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“substrate activation by uridine diphosphate glucose was observed in the absence of effectors.”
t0“Spinach”
Claim · model-written summary
Phosphate may antagonize glucose-6-P activation by competing at the modifier site.
- Taxon
- SpinachSpinacia oleraceat0
- Gene
- sucrose phosphate synthasee0
- Compound
- glucose-6-Pe0
- Outcome
- glucose-6-P activation of sucrose phosphate synthasee0
- Qualifier
- competing with the activator for binding to the modifier sitee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Pi antagonizes glucose-6-P activation of sucrose phosphate synthase by competing with the activator for binding to the modifier site.”
t0“Spinach”
Claim · model-written summary
Fructose-6-P saturation kinetics were hyperbolic without phosphoglucoisomerase activity.
- Taxon
- SpinachSpinacia oleraceat0
- Gene
- phosphoglucoisomerasee0
- Outcome
- fructose-6-P saturation kineticse0
- Qualifier
- absence of phosphoglucoisomerase activitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The fructose-6-P saturation kinetics were hyperbolic in the absence of phosphoglucoisomerase activity”
t0“Spinach”
Claim · model-written summary
Adding excess phosphoglucoisomerase made the kinetics sigmoidal.
- Taxon
- SpinachSpinacia oleraceat0
- Treatment
- addition of excess phosphoglucoisomerasee0
- Gene
- phosphoglucoisomerasee0
- Outcome
- sigmoidale0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but became sigmoidal by the addition of excess phosphoglucoisomerase.”
t0“Spinach”
Claim · model-written summary
Sigmoidicity persisted with phosphate.
- Taxon
- SpinachSpinacia oleraceat0
- Treatment
- Pie0
- Outcome
- sigmoidicity persistede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The sigmoidicity persisted in the presence of Pi”
t0“Spinach”
Claim · model-written summary
Phosphate decreased sucrose phosphate synthase activity.
- Taxon
- SpinachSpinacia oleraceat0
- Treatment
- Phosphatet0
- Outcome
- sucrose phosphate synthase activitye0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but sucrose phosphate synthase activity was decreased.”
t0“Phosphate Inhibition of Spinach”
Claim · model-written summary
The sigmoidal response may reflect enzyme response to changing hexose-P concentration.
- Taxon
- SpinachSpinacia oleraceat0
- Compound
- hexose-Pe0
- Outcome
- physiological response of sucrose phosphate synthasee0
- Qualifier
- change in hexose-P concentratione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The apparent sigmoidal response may represent the physiological response of sucrose phosphate synthase to a change in hexose-P concentration”
t0“Spinach”
The same questions in other papers
phosphorus · physiology: enzyme activity · Spinacia oleracea (spinach)Positive and negative results
1 paper in the same direction as this paper · 2 in the opposite direction
- positive
- positive
- negative
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.