Electron microscope study of native and crosslinked rabbit muscle phosphofructokinase.

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Phosphofructokinase (PFK) is a key glycolytic enzyme.
• Understanding PFK's quaternary structure is crucial for its function.
• Rabbit muscle PFK is a well-studied isozyme.

Purpose of the Study:

• To elucidate the quaternary structure of rabbit muscle phosphofructokinase.
• To characterize the assembly of PFK protomers into higher-order structures.
• To investigate the structural basis of PFK polymerization.

Main Methods:

• Electron microscopy was employed for structural analysis.
• Negative staining with sodium phosphotungstate was used.
• Dimethyl-suberimidate crosslinking stabilized protein complexes.

Main Results:

• PFK protomers (80,000 MW) were approximated as prolate ellipsoids (67 Å x 25 Å).
• Dimers (67 Å x 55 Å x 25 Å) are the fundamental polymerization units.
• Tetramers formed via end-to-end dimer association; octamers showed sheet-like structures.
• Crosslinked filaments (250 Å width, 0.5 µm length) were observed, possibly involving tetramers.

Conclusions:

• Rabbit muscle PFK exhibits a hierarchical assembly from protomers to filaments.
• The structural organization suggests mechanisms for enzyme regulation and polymerization.
• The functional role of the observed filament structures remains to be determined.