The Nature and Diversity of Catalytic Proteins 



87 



as from the loss of O 18 from P, — O 18 to water. The results show that, 

 within experimental error, the extent of exchange measured by the 

 two approaches is equal and that therefore the species undergoing 

 exchange is the inorganic phosphate of the medium. As with oxidative 

 phosphorylation, such results suggest the reversible formation and 

 hydrolysis of a phosphoryl derivative. The following points of com- 



10 



20 

 Minutes 



30 



FIG. 8. The time course c ( appearance of 18 from H L 18 into phosphate cleaved 

 from ATP by actomyosin (37). 



parison of oxidative phosphorylation and of ATP cleavage by acto- 

 myosin and myosin emerge: 



An unexplained exchange of inorganic phosphate oxygens with water 

 oxygens occurs, in both processes, possibly reflecting reversible 

 phosphorylation. 



Protein structure changes may accompany both processes. Possibility 

 of structure change accompanying electron transport is clearly 

 indicated by the difference in structure of oxidized and reduced 

 cytochrome c as indicated by the difference in proteolytic digesti- 

 bility (38) and as demonstrated by nuclear magnetic resonance 

 studies of Kowalsky (39) in our laboratory. 



