282 TERU HAYASHI 



ess is still going on (T. Hayashi and H. C. Lamont, unpublished re- 

 sults). 



It is quite possible to interpret these results by mechanisms other 

 than the alternatives stated above, but they will reduce, I believe, to 

 complicated combinations of these alternatives, and necessitate added 

 assumptions. The question is, "Is the 'relaxing factor' acting as a 

 'structure loosener' (plasticizer) or as a 'contractile-process reverser' 

 (which may involve ATPase inhibition) in bringing about the re- 

 laxation phenomenon?" 



All this is not to be taken as discrediting the work on "simplified 

 systems." I am saying only that data are data and must be scrutinized 

 for their limitations. With this in mind, we may now examine the 

 question of contractile proteins in flagella. 



It is interesting that a myosin-like protein has been found in sperm 

 flagella by the Russian workers (see Bishop, this symposium). But 

 work Avith muscle proteins has shown that myosin and actin together 

 are an absolute requirement for contraction (Hayashi et al., 1958). 

 If we assume that the same prevails in sperm-tail proteins, then it 

 behooves one to look for an actin-like protein. This may not be too 

 difficult, for methods for extracting actin from muscle have been 

 worked out quite completely (Ulbrecht et al., 1960). 



A very strong indication of the presence of actin may be obtained 

 even more easily. Actin is characterized by having a nucleotide (either 

 ATP or ADP) bound to it (Straub and Feuer, 1950), and this fact 

 can be utilized analytically. An extract can be cleared of its con- 

 taminating, unbound nucleotides (Tsuboi and Hayashi, 1959), and 

 once this is done, the bound nucleotide can be determined. If any 

 exists, a strong presumption of the presence of actin would be indi- 

 cated, and therefore the presence of a complete contractile system in 

 the sperm tail. This information would be of importance, and I sug- 

 gest that the "spermiologists" use this technique to establish it. 



REFERENCES 



Chance, B. 1959. The response of mitochondria to muscular contraction. 

 Ann. N. Y. Acad. Sci., SI, 477-489. 



Hayashi, T., R. Rosenbluth, P. Satir, and M. Vozick. 1958. Actin par- 

 ticipation in actomyosin contraction. Biochim. et Biophys. Acta, 28, 

 1-8. 



