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Cytosolic ATP-Dependent Phosphofructokinase from Spinach
R E Häusler1, J A Holtum, E Latzko
1Botanisches Institut, Westfälische Wilhelms-Universität, Schlossgarten 3, 4400 Münster, Federal Republic of Germany.
Plant Physiology
|June 1, 1987
Summary
Spinach leaves possess cytosolic ATP-dependent 6-phosphofructokinase (PFK) activity, distinct from chloroplast PFK. This cytosolic enzyme is stimulated by inorganic phosphate (Pi) and plays a key role in plant metabolism.
Area of Science:
- Plant Biochemistry
- Enzymology
- Metabolic Pathways
Background:
- ATP-dependent 6-phosphofructokinase (PFK) is a crucial enzyme in glycolysis.
- PFK activity in plants has been localized to both chloroplasts and other cellular compartments.
- Understanding the specific roles and characteristics of different PFK isoforms is essential for elucidating plant metabolic regulation.
Purpose of the Study:
- To characterize and differentiate ATP-dependent 6-phosphofructokinase (PFK) activities in spinach leaves.
- To investigate the presence and properties of cytosolic PFK in spinach.
- To determine the effect of inorganic phosphate (Pi) on PFK activity in different spinach cellular fractions.
Main Methods:
- Isolation of chloroplastic and non-chloroplastic fractions from spinach protoplasts.
- Assay of ATP-dependent 6-phosphofructokinase (PFK) activity in isolated fractions.
- Enzyme fractionation using ammonium sulfate precipitation.
- Characterization of enzyme properties, including response to inorganic phosphate (Pi) and pH.
Main Results:
- ATP-dependent 6-phosphofructokinase (PFK) activity was detected in both chloroplastic and extra-chloroplastic fractions of spinach protoplasts.
- Extra-chloroplastic PFK activity was significantly stimulated by inorganic phosphate (Pi), while chloroplast-associated PFK was inhibited by Pi.
- Ammonium sulfate fractionation confirmed the presence of distinct PFK activities, separable from pyrophosphate fructose 6-P 1-phosphotransferase (PFP), and identified a cytosolic PFK.
Conclusions:
- Spinach leaves contain a distinct cytosolic ATP-dependent 6-phosphofructokinase (PFK) activity.
- This cytosolic PFK is relatively stable, stimulated by inorganic phosphate (Pi) over a broad pH range, and exhibits activity comparable to cytosolic PFP.
- The findings differentiate cytosolic PFK from chloroplast PFK and highlight its potential role in plant carbon metabolism.