Phosphofructokinase-1 from Saccharomyces cerevisiae: analysis of molecular structure and function by electron microscopy and self-catalysed affinity labelling

Conventional and cryoelectron microscopy portray native octameric yeast phosphofructokinase-1 (PFK) as consisting of two identical heterotetrameric tetrahedron-like moieties being rotated relative to each other. Immunoelectron microscopy employing subunit-specific IgG identifies alpha-type subunits in the contact zone of the two tetrahedrons, while beta-chains are recognized exclusively at the tips of the octamer. The chemical reaction of phosphofructokinase with analogues of fructose 6-phosphate followed by autocatalytic phosphoryl transfer from [gamma-32P]-ATP results in a specific labelling of the alpha-subunit. AMP and fructose 2,6-bisphosphate affect labelling by stimulating the binding of substrate analogue; AMP additionally promotes phosphoryl transfer. No stimulation of labelling is observed with proteolytically modified tetrameric 12-S phosphofructokinase.