Mouse muscle phosphofructokinase is partially phosphorylated.

Phosphofructokinase isolated from mouse skeletal muscle 18 hours after intraperitoneal injection of [${}^{32}\text{P]-}\text{PO}{}_4{}^{\mathrm{3?}}$ contained 0.12 to 0.15 moles of covalently bound phosphate per protomer on the basis of the specific activity of radiolabel in the γ-position of ATP. Under identical conditions, muscle pyruvate kinase and aldolase had no covalently bound phosphate.