Isozyme composition and phosphorylation of brain phosphofructokinase

Area of Science:

• Biochemistry
• Enzymology

Background:

• Phosphofructokinase (PFK) is a key glycolytic enzyme.
• Rabbit brain PFK is a complex enzyme composed of multiple subunits.

Purpose of the Study:

• To purify and characterize rabbit brain phosphofructokinase.
• To investigate the phosphorylation of rabbit brain PFK and its effects on enzyme activity.

Main Methods:

• Purification of PFK using affinity chromatography and gel filtration.
• In vitro phosphorylation assays using cyclic AMP-dependent protein kinase.
• Analysis of subunit composition and phosphorylation sites.

Main Results:

• Purified rabbit brain PFK consists of subunits C, A, and B (MW 86,000, 84,000, 80,000) in a 5:4:1.5 ratio.
• The enzyme contains endogenous phosphate, and additional phosphate can be incorporated in vitro.
• In vitro phosphorylation did not affect enzyme activity, ATP inhibition, or fructose 2,6-bisphosphate activation.

Conclusions:

• Rabbit brain PFK is a hybrid enzyme with distinct subunit types.
• In vitro phosphorylation of rabbit brain PFK does not alter its catalytic properties or regulatory responses.