A novel type of phosphofructokinase from plants

Area of Science:

• Biochemistry
• Plant Physiology
• Enzymology

Background:

• Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis.
• Plant cytosolic PFK exhibits distinct properties compared to mammalian PFK.
• Understanding PFK regulation is crucial for deciphering carbon flux in plants.

Purpose of the Study:

• To purify and characterize phosphofructokinase (PFK) from carrot roots.
• To investigate the different forms and regulatory mechanisms of plant PFK.
• To explore the role of PFK aggregation in controlling glycolytic flux.

Main Methods:

• Purification of phosphofructokinase (PFK) to homogeneity from carrot roots.
• Analysis of enzyme molecular weight, subunit composition, and aggregation states.
• Characterization of enzyme kinetics, pH optima, and regulatory properties.

Main Results:

• Carrot PFK was purified as a large aggregate (>5 million Da) with a lower subunit molecular weight (60,000 Da) than mammalian PFK.
• PFK exists in multiple forms (small, intermediate, large) influenced by ATP, fructose-6-phosphate, and pH.
• Different PFK forms displayed unique pH optima and regulatory responses to metabolites like ATP, citrate, and phosphoenolpyruvate.

Conclusions:

• Metabolite-dependent aggregation-disaggregation is a key regulatory mechanism for plant cytosolic PFK.
• This mechanism allows plants to control glycolytic carbon flux.
• Similar PFK properties were observed in spinach leaf cytosolic PFK, suggesting a conserved regulatory strategy in plants.