FREE-ENERGY RELATIONS AND CONTRACTION OF ACTOMYOSIN

Abstract

According to the AF curve of Varga the expenditure of F (free energy) of the single functional units of muscle increases with temp. If the F of ATP is used for relaxation, as indicated by this curve, then the muscle should be unable to relax at a temp. where the expenditure of its units reaches 11,000 cal. This has been found to be the case. The total work of the frozen psoas, performed on thawing, agrees with Varga''s curve if calculated for units of myosin of MW 35,000 g. The isotonic results agree over the whole range of measurements. The isometric results agree up to 5500 cal. which is half of the expected maximal tension. At this point tension reaches maximum. The behavior of the fresh frozen frog muscle is at variance with Varga''s curve. If treated with chloroform, it behaves as predicted by this curve. The contraction of chloroform-treated frog muscle and the contraction of washed psoas muscle in ATP are thermo-dynamically reversible. The fresh psoas shows limited high elasticity. If the ATP is decomposed or washed out the muscle becomes inelastic. Elasticity can be restored by the addition of ATP. The elasticity is a function of temp. The wt. of the functional units of myosin can be calculated from the work done and is between 35,000 and 70,000 g.