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Phosphate dependency of phosphofructokinase 2.

M Laloux, E Van Schaftingen, J Francois

European Journal of Biochemistry

|April 1, 1985

Summary

Liver phosphofructokinase 2 activity is highly dependent on inorganic phosphate, essential for its function. This phosphate requirement is consistent across species and enzyme forms, unlike its fructose 2,6-bisphosphatase activity.

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Area of Science:

Biochemistry
Enzymology
Metabolic Regulation

Background:

Phosphofructokinase 2 (PFK2) is a key enzyme in glycolysis and gluconeogenesis, catalyzing the formation of fructose-2,6-bisphosphate.
The regulation of PFK2 activity is crucial for maintaining cellular energy homeostasis and metabolic flux.
Understanding the specific requirements and regulatory mechanisms of PFK2 is vital for comprehending metabolic control.

Purpose of the Study:

To investigate the role and dependency of inorganic phosphate on the activity of liver phosphofructokinase 2.
To characterize the kinetic effects of inorganic phosphate on PFK2 and its fructose 2,6-bisphosphatase activity.
To determine if enzyme phosphorylation affects the phosphate dependency of PFK2.

Main Methods:

Enzyme kinetic assays were performed using varying concentrations of inorganic phosphate, fructose 6-phosphate, and ATP.
The effects of pH, citrate, and P-enolpyruvate on enzyme activity were assessed.
Enzyme phosphorylation was induced using the catalytic subunit of cyclic-AMP-dependent protein kinase.

Main Results:

Liver phosphofructokinase 2 exhibits complete inactivity in the absence of inorganic phosphate or arsenate, demonstrating a strong phosphate dependency.
Phosphate increased Vmax and decreased Km for fructose 6-phosphate, without affecting Km for ATP.
Fructose 2,6-bisphosphatase activity of the bifunctional enzyme was not phosphate-dependent but was modulated by phosphate concentration.

Conclusions:

Inorganic phosphate is essential for phosphofructokinase 2 activity, influencing its catalytic efficiency and substrate affinity.
The phosphate dependency of PFK2 is conserved across different species and enzyme forms.
Phosphorylation by PKA does not alter the fundamental phosphate requirement of PFK2, highlighting distinct regulatory mechanisms for its two activities.

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