Myofibrils of skeletal muscle : the activity coefficient of orthophosphate

In the kinetic model of the cross-bridge cycle the rate limiting steps are dependent on the number of cross-bridges in the strongly bound. To analyze the orthophosphate concentration impact we studied the free energy of hydrolysis of ATP in muscle. We determined that at the physiological protein osmotic pressure the orthophosphate showed a classic activity coefficient (0.85) in the myofibrils of skeletal muscle Under the same conditions and at saturation, 2.67 mumoles of orthophosphate are bound per gram of dry myofibrils, with a dissociation constant of 7 x 10(-5) molal. Work is in progress to determine the activity coefficients of adenine nucleotide analogues.