ATPASE AND ACETYLCHOLINESTERASE OF SPERM 241 



ing the ATPase of a perch sperm tail suspension in the presence of 

 substrate. A reduction in optical density of between 15% and 20% 

 occurred. This seems to indicate a swelling of the sperm tails. Out of 

 a total of 17 preparations, 10 were active to about the extent just de- 

 scribed, 3 had small activity, and 4 were inactive. Calcium but not 

 barium could replace magnesium as activator, the effect taking place 

 at a much reduced rate. Calcium will also activate the flagellar ATP- 

 ase but is less effective than magnesium (Tibbs, 1959). Adenosine di- 

 phosphate (ADP), adenosine monophosphate (AMP), inosine triphos- 

 phate (ITP), sodium pyrophosphate, and sodium triphosphate were 

 all tested for their ability to replace ATP. ADP replaced ATP quite 

 satisfactorily, the other substrates being without effect. ADP was also 

 hydrolyzed by the sperm tail preparations about 30% as effectively as 

 ATP. This is in line with the observations of other workers (Nelson, 

 1954; Engelhardt and Burnasheva, 1957), although in the past the 

 author has had preparations which did not seem to hydrolyze ADP 

 (Tibbs, 1959). 



To provide more convincing evidence that the optical density 

 change was really connected with ATP hydrolysis the effect of alter- 

 ing the MgCl 2 in the presence of EDTA was investigated. Results 

 graphed in Fig. 4 were obtained from the same preparation as that 

 which was used for the results shown in Fig. 2. In each case the same 

 solutions in the same concentrations were used. Optical density meas- 

 urements were made at room temperature and ATPase determina- 

 tions at 37°. Otherwise the only difference between Fig. 2 and Fig. 4 

 is that the former relates to ATPase activity, the latter to optical den- 

 sity changes. Mg++ and EDTA obviously influence the optical den- 

 sity effect in exactly the same way as they influence the enzyme activ- 

 ity, little change occurring until the Mg++ concentration exceeds the 

 EDTA. Although the precise form of the curves in Fig. 4 may be in 

 some doubt, the general conclusion is inescapable. 



Further evidence for the connection between optical density 

 changes and ATPase activities was provided by the use of inhibitors. 

 Lack of opportunity prevented these experiments being widened in 

 their scope, but Fig. 5 shows the effect of three different salts on the 

 enzyme activity. NaF (10 _2 M) caused more than 50% inhibition of 

 the enzyme, and in the same concentration NaCl and NaCN had lit- 

 tle effect. On increasing the salt concentration to 10 -1 iU the fluoride 



