CYTOCHEMICAL ASPECTS 



179 



hibitors, and inorganic pyrophosphate. Of particular interest is the 

 last-named substance; sodium pyrophosphate (NaPP) delays the di- 

 lution-precipitation of washed suspension of Mytilus sperm tails, 

 while ATP has an accelerating effect. Moreover, among other en- 

 zymes found in these isolated flagella is a highly active inorganic 

 pyrophosphatase (IPPase), the substrate of which, NaPP, in appro- 

 priate concentrations inhibits the ATPase and competes with the 

 flagellar ATPase for Mg (Nelson, 1959a). This enzyme, also concen- 

 trated in the peripheral fibers of mammalian sperm flagella (Fig. 

 6), is soluble in 50% glycerol, whereas the ATPase is stable (Nelson, 

 1959c), and remains in situ. One possible interpretation of the repet- 

 itive twitch behavior of Bishop's glycerinated sperm models (Bishop, 

 1958a,b) contrasted to the oscillations of fresh sperm is that progres- 

 sive movement requires the reciprocal interaction of at least two 



Fig. 5. Diagram of transverse section of rat sperm midpiece. Dotted 

 line through central pair of fibers indicates plane of symmetry and pos- 

 sibly of undulation. 



