184 LEONARD NELSON 



Vorobiev (1957) and Ashmarin (1953) claim that myosin in vitro 

 complexes with other polyelectrolytes besides actin to produce con- 

 tractile threads, this does not warrant the conclusions that actin or 

 an actin-like protein is absent from sperm. Hayashi et al. (1958) have 

 shown that finite quantities of actin are required to confer contrac- 

 tility on purified myosin; and Pautard (this symposium) claims to 

 have found actin in fish sperm. Perhaps the hypothetical actin ho- 

 molog of mammalian sperm resists extraction by methods suitable 

 for its removal from muscle. Alternatively, the other-protein inter- 

 action in mammalian sperm may be of such a nature that the spermo- 

 sin is freely extractable, leaving the actin-like moiety bound to a 

 different flagellar component. Should this be the case, the binding 

 sites on spermosin in situ could perhaps be accessible to the non- 

 flagellar actin. Preliminary tests, in which frozen-dried rat sperm 

 were incubated in purified G-actin solutions, give the distinct im- 

 pression that the muscle actin is adsorbed on the surface of the pe- 

 ripheral fibers and fills the matrix between the fibers, while bovine 

 serum albumin of approximately the same concentration (0.1%) does 

 not appear to combine with any flagellar structure. Prior extraction 

 of the frozen-dried sperm with 0.6M KI in Na 2 S 2 3 interferes with 

 the increase in electron density attributed to the actin adsorption 

 (Fig. 10). 



It may be premature at this juncture to speculate on the actin- 

 spermosin interaction in terms of complementarity or other type of 

 macromolecular affinities. The time scale imposed by the contraction- 

 relaxation cycles necessitates the formation of a freely dissociable 

 complex. The logical site for the actin-like member of such a com- 

 plex would be within the axial fiber system, although Varga and co- 

 workers (1955) associate the L-meromyosin fraction of skeletal muscle 

 with acetylcholinesterase (assuming the acetylcholinesterase of mam- 

 malian sperm to be within the axial core). More direct evidence may 

 have to await the application of purified actin antibodies in the cyto- 

 chemical procedures, in conjunction with prolonged extractions in 

 high ionic strength media. 



What may we conclude from the present cytochemical considera- 

 tions that may lend substance to our speculations on the morphologi- 

 cal basis of sperm motility? Some of the necessary ingredients for the 

 generation and regulation of the undulatory wave have been identi- 



