ATPASE AND ACETYLCHOLINESTERASE OF SPERM 



235 



tration after a maximum value has been obtained, the decrease is far 

 less dramatic than in the corresponding case of the myofibril, and it 

 is hardly possible to believe that this inhibition is basic to an effective 

 relaxation mechanism. It would be of interest to consider the effect 

 of muscle relaxing factor on the sperm tail ATPase, but results on this 

 aspect of the work have not, up to date, been of much use since the 

 muscle relaxing factor is unfortunately associated with a granular 

 fraction (Portzehl, 1957) which itself carries an ATPase. In estima- 

 tions where the myofibrillar enzyme is mixed with relaxing factor, 

 the ATPase of the latter is a good deal smaller and can be allowed for. 

 The sperm tail enzyme is much less active, and in suspensions which 

 contain added muscle relaxing factor the enzyme activity of the latter 

 is dominant. Nevertheless the idea may be worth pursuing in view 

 of the fact that Bishop and Hoffmann-Berling (1959) report that mus- 

 cle relaxing factor inhibits the flagellation of sperm models. 



Attempts have also been made to obtain evidence for the existence 



Fig. 1. Effect of substrate concentration on the splitting of ATP by 

 three preparations of flagella. Carried out in 0.1M borate buffer pH 8.2. 

 O- in presence of 2.5 raM MgCl 2 ; 9 , in presence of 5.0 mM MgCL; A, in 

 presence of 7.5 mM MgCl 2 . 



