Catalyzes the phosphorylation of D-fructose 6-phosphate to fructose 1,6-bisphosphate by ATP, the first committing step of glycolysis (PubMed:33540748). Can also catalyze the phosphorylation of tagatose-6-phosphate. Both sugar phosphates can function equivalently as substrates (PubMed:33540748). Cannot catalyze the reverse gluconeogenic reaction (PubMed:33540748). ATP + beta-D-fructose 6-phosphate = ADP + beta-D-fructose 1,6-bisphosphate + H(+) ATP + D-tagatofuranose 6-phosphate = ADP + D-tagatofuranose 1,6-bisphosphate + H(+) Magnesium may play a role in formation and maintaining of proper enzyme conformation and multimerization. Inhibited by high concentrations of the substrates fructose 6-phosphate and ATP, and by the reaction products, fructose 1,6-bisphosphate and ADP. Allosterically inhibited by phosphoenolpyruvate (PEP), guanosine diphosphate (GDP) and citrate. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 3/4. Homodimer or homotetramer. Activity of PfkA is tenfold higher than that of PfkB (PubMed:33540748). Activity with tagatose-6-phosphate suggests that PfkA and/or PfkB may substitute for tagatose-6-phosphate kinase and further support glycolysis (PubMed:33540748). Belongs to the phosphofructokinase type A (PFKA) family. Mixed-substrate PFK group III subfamily.