Intracellular concentration of skeletal and cardiac muscle phosphofructokinase in diabetic and normal animals.

An RIA has been developed for rabbit muscle PFK, an allosteric enzyme which catalyzes the pacemaker reaction of glucose utilization. The assay which could accurately measure as little as 12 ng (37.5 fmol) of the tetrameric enzyme was applied to extracts of skeletal and cardiac muscle of animals subjected to four different nutritional conditions and to alloxan diabetes. The concentration of enzyme remained unchanged in all conditions: mean value in anterior tibial muscle was 2.99 microM (S.D., 0.20; N, 32); in left ventricle, 0.66 microM (S.D., 0.07; N, 29). It may be concluded that control of the reaction is mainly, if not exclusively, by allosteric phenomena and not by insulin- or nutrition-dependent changes in intracellular concentration of the enzyme.