MYOFIBRIL-BOUND MUSCLE PHOSPHOFRUCTOKINASE IS LESS SENSITIVE TO INHIBITION BY ATP THAN THE FREE ENZYME, BUT RETAINS ITS SENSITIVITY TO STIMULATION BY BISPHOSPHORYLATED HEXOSES

Phosphofructokinase activity is modulated by allosteric effecters and macromolecular interactions (e.g. binding to myofibrillar components), The aim of this study was to determine the effects of ATP and bisphos phorylated sugars upon phosphofructokinase in the presence of myofibri ls. Myofibrils were prepared from resting and electrically stimulated rat muscle, Dephosphorylation of myofibrils was performed with alkalin e phosphatase acid, Purified rabbit skeletal muscle phosphofructokinas e was used for all experiments, Myofibrils from resting muscle showed a higher capacity to bind phosphofructokinase and a lower phosphate co ntent than myofibrils from stimulated muscle. Dephosphorylation of myo fibrils did not increase their binding capacity, Myofibrils greatly co unteracted the inhibition of phosphofructokinase by high concentration s of ATP, without affecting maximum activity, In the presence of myofi brils, both glucose 1,6-bisphosphate and fructose 2,6-bisphosphate add itionally activated muscle phosphofructokinase. We suggest that the bi nding of phosphofructokinase to myofibrils in combination with increas ing glucose 1,6-bisphosphate concentration could be important in the e nhancement of the glycolytic flux that takes place during muscle contr action. Copyright (C) 1996 Elsevier Science Ltd