KARL F. GUTHE 



79 



form, which may therefore correspond to the present native form. This 

 suggests that anyosin in its gel-forming state is not an active ATP-ase. 

 Although the denatured form has been considered completely inactive, 

 for simplicity, the data do not exclude a possible small activity. 



The heats and volumes observed by Laidler, Morales and their associates 

 (12, 20) for myosin B ATP-ase agree with our measurements, although 

 our interpretation leads to apparently different values. They have also 

 determined the relative contributions of electrostatic and configurational 



Table 1. Heats and volumes determined for the 



MYOSIN ADENOSINETRIPHOSPHATASE SYSTEM 



High substrate (4, 9) 

 E + Ca ;=^ ECa 



Temperature, 0H~ tt^ i p 

 Pressure, H+ 



Temperature, 0H~ ^ , 



Native ^ Denatured 



Pressure, H+ 



PrGSSurG 

 Myosin B gel . ^ ' sol (14) 



Temperature 



High substrate (12, 20) 



Phosphate split 

 Low substrate (12, 20) 



Formation of ES complex 



Av OR Av* 

 cc/mole 



small 

 +60 



+ 100 



+ 120 



-32 to -251 



+8 to +231 



Ah or Ah* 



cal/mole 



small 

 +31,000 



+ 12,600 



+ 12,400 

 +8,000 



1 Volume changes become more positive as KCl increases. 



effects to the entropy changes in the ATP-ase system (13). Both effects 

 play a significant role at both high and low substrate concentrations, but 

 it is not yet clear how the relative contributions of these two effects are 

 partitioned among the various reactions. Reversible denaturation may be 

 important at both high and low substrate concentrations, since the rela- 

 tion of this reaction to the Michaelis-Menten reaction scheme is uncertain. 

 The sensitivity of reversible denaturation to pressure, temperature and 

 hydrogen ions has been the main subject of this paper. A sensitivity to 

 other ions might explain the dependence of the apparent volume of activa- 

 tion on KCl concentration (12). The equilibrium may also play a part 

 in other aspects of the myosin problem, such as the pH-dependence of the 

 apparent Michaelis-Menten constant (8) and the existence of deformed 



