86 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



a reversible denaturation inactivation of the myosin ATPase establishes 

 the concentration of active native enzyme. In simplified form with ref- 

 erence to myosin alone the overall reaction may be written: 



(R) 

 (RD) 



ATP 



Mi 



in which the steady state production of P depends on reaction (R) cata- 

 lyzed by the enzyme Ma , while the amount of the catalytically active 

 form of this enzyme is subject to a reversible decrease through the 

 denaturation equilibrium (RD). In the formation of products, the equi- 

 librium (RD) is characterized by AH = 12,000 cal. and aV = +120 

 cc/mole, while the rate process (R ) is characterized by AH* = 30,000 

 cal. and AV* = +60 cc/mole. The effect of increased pressure is to in- 

 crease the amount of active enzyme, thereby favoring a faster rate of 

 formation of P, while at the same time to retard the rate of the enzyme re- 

 action itself, thereby slowing the formation of P; the net result of pres- 

 sure is governed by the differences in the values of aV and aV*, respec- 

 tively. 



In relation to contraction, the myosin ATPase reaction exhibits two 

 properties essential in the contractile system. First, the reversible de- 

 naturation (RD), with its large volume change, offers a device for the 

 conversion of myosin from a denatured inactive form to a native active 

 form with potential shortening properties and simultaneously estab- 

 lishes the concentration of active myosin ATPase. Secondarily, the myosin 

 ATPase, thus controlled, provides for the regulated involvement of high 

 energy phosphate from the jiool of phosphate donors and acceptors. 



Although the existence of the RD reaction in relation to myosin ATPase 

 is demonstrated (10), it remains to be shown that the RD affects other 

 properties of the myosin molecule such as its reaction with actin. The 

 ready solation of (i myosin gels by pressure accompanied by a volume 

 decrease, aV, of 120 cc/mole suggests that the RD may be involved in 

 the formation of actomyosin gels (11). Further evidence of the partici- 

 pation of the RD in the contraction of glycerated or normal fibers can be 

 found in the methods of thermodynamic and kinetic analysis. 



THE GLYCERATED FIBER 



The discovery of the contractility of glycerated fibers by Szent Gyorgyi 

 (12) opened the way to investigations of myosin and actin within the 

 structural organization of a fiber ajiproximating that of living muscle. 

 Physico-chemical studies of contractility in relation to temperature, pH, 



