ATPASE AND ACETYLCHOLINESTERASE OF SPERM 245 



the effect was obtained. This was disappointing, but it would appear 

 that some stimulus other than simply the cessation of ATP splitting 

 is necessary to restore the nagellum to its original size. 



It is suggested therefore that the completely relaxed state in the 

 case of sperm tails is one of minimum volume and is thus the opposite 

 of the myofibril in this respect. Activation of all the sites of enzyme 

 activity in the presence of substrate results in maximum swelling. 

 Presumably between these two extremes is the state of the flagellum 

 during motility where those enzymic sites which are hydrolyzing ATP 

 cause localized swelling. Other sites prevented from splitting their 

 substrate, possibly by the nonavailability of free ATP, do not show 

 this swelling. The combination of substrate-splitting sites, which give 

 rise to a corresponding tail configuration, is changing all the time. 



Glycerol-extracted sperm and, in a few instances, glycerized sperm 

 tails have been used as model systems (Bishop and Hoffmann-Berling, 

 1959). These models have provided and no doubt will continue to 

 provide very useful information but for a study of the biomechanics 

 of motility they suffer from two disadvantages. The presence of at 

 least some midpiece components appears to be necessary before the 

 models will flagellate (Bishop and Hoffmann-Berling, 1959), and ATP 

 splitting takes place at some enzymic sites and is presumably absent 

 at others. The very multiplicity of processes which must be taking 

 place in these models makes the results difficult to interpret. Extracts 

 of proteins involved in the mechanism have not proved easily ob- 

 tainable (Bishop, 1958a), and in any case the behavior of such ex- 

 tracts is always difficult to relate to the behavior of the living material. 



It is likely that the preparations described here will provide a use- 

 ful model system which, in any case, will be complementary to the 

 two mentioned above. Thus, if the biological process which accom- 

 panies ATP splitting has really been observed, and this seems to be 

 the case, factors influencing this process can now be examined quite 

 easily. 



SPERM CELLS AND ACETYLCHOLINESTERASE 



The generally accepted mechanism of nervous excitation require*, 

 the participation of the enzyme acetylcholinesterase. In the case of 

 neuromuscular control this enzyme is probably also a constituent of 



