Catalyzes the phosphorylation of the ketose sugar fructose to fructose-1-phosphate. ATP + beta-D-fructose = ADP + beta-D-fructose 1-phosphate + H(+) Requires potassium. Inhibition by ADP. Carbohydrate metabolism; fructose metabolism. Homodimer. Isoform C is most abundant in liver, kidney, gut, spleen and pancreas. Low levels of isoform A found in adrenal, spleen and brain. The N-terminus is blocked. Belongs to the carbohydrate kinase PfkB family.