Phosphofructokinase (PFK) is a tetrameric enzyme that catalyzes a key step in glycolysis, namely the conversion of D-fructose 6-phosphate to D-fructose 1,6-bisphosphate. Separate genes encode a muscle subunit (M) and a liver subunit (L). PFK from muscle is a homotetramer of M subunits, PFK from liver is a homotetramer of L-subunits, while PFK from platelets can be composed of any tetrameric combination of M and L subunits. The protein encoded by this gene represents the L subunit. Alternate splicing results in two transcript variants, one of which is a candidate for nonsense-mediated decay (NMD). [provided by RefSeq, Aug 2008].