The synergetic enzyme theory of muscular contraction: II Relation between Hill's equations and functions of two-headed myosin

Abstract

Based on the assumption of nonidentical two heads of myosin it is pointed out that a strong motive force is generated in actomyosin pair only when ATP-decomposition occurs co-operatively at the both heads and that the tension-independent part of shortening heat is liberated when an ATP molecule is decomposed only at the burst head. These two actions of actomyosin pair are related to the two states of force-generator in Huxley-Simmons' model. Elementary cycles at different positions in a sarcomere are interacted each other through feedback loop via sliding motion of muscular filaments. Due to this synergetic interaction the rate constant for the rate-determining step of elementary cycle has a dependence on velocity v of shortening such as k = k ° + κv. From these functions and properties of actomyosin system in vivo, the following properties of muscle are explained consistently in a quantitative manner: (1) Hill's equation on the relationship between tension and velocity of shortening, (2) damped oscillations in tension and in muscular length around steady state, (3) Hill's energy equation improved in 1964, (4) the chemical equivalence of shortening heat, (5) the influence of tension on the incorporation of radio-active phosphate into ATP and (6) the asymmetric activation by actomyosin system only for the forward reaction, the decomposition of ATP.