BIOLOGY OF SPERMATOZOA 



767 



certain theoretical assumptions underlying 

 the analysis (Rothschild, 1953, 1959; Nel- 

 son, 1958b). 



At the present time, such information 

 may seem limited in its application to 

 problems of sperm physiology in relation to 

 the reproductive process as a whole. From 

 a broad point of view, however, it obviously 

 affords a biophysical measure of what the 

 sperm can accomplish, and constitutes a 

 link between the metabolic energy produced, 

 on the one hand, and the work performed 

 during activity, on the other (Table 13.12). 



D. MECHANISM OF MOTILITY 



Speculation concerning the physical basis 

 for activity of cilia and, by implication, 

 flagella has a long tradition (Grant, 1833; 

 Ankermann, 1857; Schafer, 1904). Of the 

 various theories proposed, the only one to 

 persist is that which conceives of the flagel- 

 lum as a diminutive contractile system 

 (Ciaccio, 1899; Koltzoff, 1903; Ballowitz, 

 1908; Heidenhain, 1911). Other types of 

 biochemical systems can be imagined to ac- 

 count for sperm movement, but the evi- 

 dence, particularly of the past few years, 

 favors the concept of a contractile protein 

 mechanism, generally associated with the 

 fibrillar system of the tail (see Bishop, 

 1961). 



Brief mention has been made of certain 

 salient features of the motility process. 

 It is clear that ATP is essential for sperm 

 activity, as it is for many other physiologic 

 processes reciuiring energy. A constant suji- 

 ply of ATP is maintained by the glycolytic 

 and/or oxidative processes of metabolism 

 (Engelhardt, 1958 j. Certain experiments 

 have indicated that extractable ATP is not 

 significantly depleted during sperm activity 

 (Hultin, 1958), thus further supporting the 

 view that resynthesis of the nucleotide ac- 

 companies its dephosphorylation. The pres- 

 ence and general localization of ATPase in 

 the flagellum have been noted; by its spe- 

 cific action on ATP as substrate, chemical 

 energy associated with ''high-energy" phos- 

 phate bonds is liberated. 



The ATP-ATPase type of enzyme sys- 

 tem is widely distributed throughout the 

 animal and plant kingdoms; it has been 

 extensively studied and closely identified 

 Avith the contractile svstem of muscle. It 



was of major significance that the con- 

 tractile protein itself, myosin, was found 

 to possess the ATP-splitting activity which 

 leads to contraction (Engelhardt and Lyu- 

 bimova, 1939). ATPases thus represent the 

 essential link between the biochemical and 

 mechanical events (Engelhardt, 1958). 

 Myosin alone is incapable of shortening, but 

 when combined with actin, the complex un- 

 dergoes contraction in the presence of ATP. 

 This can be readily demonstrated in simpli- 

 fied muscle systems such as glycerinatetl 

 fiber models (Szent-Gyorgyi, 1949; Varga, 

 1950) or actomyosin thread preparations 

 (Portzehl and Weber, 1950). 



As a result of their previous studies of 

 the biochemistry of muscle, and the overt 

 similarities of muscle contraction and 

 sperm flagellation, Engelhardt and his as- 

 sociates undertook a detailed study of mo- 

 tility of bull sjierm. They extracted from 

 sperm cell homogenates a partially purified 

 l)rotein which showed ATPase activity and 

 was tentatively called "spermosin" (Engel- 

 hardt, 1946). Refinements in extraction and 

 luirification procedures since that time have 

 resulted in tlie jireparation of a product with 

 many of the properties of myosin, isolated 

 by similar techniques from muscle. Mean- 

 while, work was being reported from several 

 other laboratories confirming the occurrence 

 of ATPase in sperm and sperm tail prepa- 

 rations of a variety of species (Felix, 

 Fischer, Krekels and Mohr, 1951 ; Nelson, 

 1954, 1955b; Utida, Maruyama and Nanao, 

 1956; Bishop, 1958a; Tibbs, 1959). Although 

 not all of these preparations are unequivo- 

 cally associated with contractile protein or 

 contractile protein alone, the evidence seems 

 clear that the sperm tail possesses high 

 ATPase activity. 



More recent publications from Engel- 

 hardt's institute indicate that material of a 

 high degree of purity can be extracted from 

 bull sperm tails which probably is the con- 

 tractile protein, "spermosin," responsible 

 for movement (Engelhardt and Burnasheva, 

 1957; Burnasheva, 1958; Engelhardt, 1958). 

 Ai^iiroximately 80 per cent of the ATPase 

 activity of the whole sperm is concentrated 

 in the tail fraction, isolated by centrifuga- 

 tion. Substrate specificity and cationic re- 

 quirements of the enzyme have led to the 

 conclusion that it is very similar to muscle 



