Regulatory subunit of pyrophosphate--fructose 6-phosphate 1-phosphotransferase. Allosterically activated by fructose 2,6-bisphosphate. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 3/4. Tetramer of two alpha (regulatory) and two beta (catalytic) chains. Belongs to the phosphofructokinase type A (PFKA) family. PPi-dependent PFK group II subfamily. Clade 'Long' sub-subfamily.