BIOLOGY OF SPERMATOZOA 



7(>9 



of the surrounding medium (Bishop, 1958f ; 

 Bishop and Hoffmann-Berling, 1959). 



Such biochemical approaches as these 

 suggest that the molecular basis of sperm 

 motility is very similar to that of the con- 

 tractile protein system of muscle. The 

 identification of this system in the sperm is 

 less securely established, but it is assumed 

 to be localized in the longitudinal fibrils of 

 the flagellum. The universality of the 2 

 X 9 + 2 pattern of filaments seems to de- 

 mand that considerable significance be at- 

 tached to them. The filaments appear on 

 chemical grounds to resemble a fibrous pro- 

 tein which could be contractile in nature. 

 Both solubility data (Schmitt, 1944; Brad- 

 field, 1955) and the results of proteolytic 

 digestion of sperm flagella (Hodge, 1949; 

 Grigg and Hodge, 1949) support this view. 

 The positive form birefringence of sperm 

 tails further indicates an orderly arrange- 

 ment of highly asymmetric structural units 

 which may indeed be the components of the 

 longitudinal fibrils themselves (Schmitt, 

 1944). X-ray diffraction measurements also 

 suggest a high degree of organization with 

 regular spacing of the structural elements 

 (Lowman and Jensen, 1955). These reports 

 on sperm flagella do not prove that the 

 longitudinal fibrils are contractile protein, 

 but they lend credence to that assumption. 

 Excellent supporting evidence, moreover, is 

 that obtained by Astbury and Weibull 

 ( 1949) in their study of an entirely different 

 type of flagellar system, the isolated flagella 

 of bacteria. These investigators concluded 

 that the x-ray diffraction pattern of flagellar 

 preparations is characteristic of the k-m-e-f 

 group of fibrous proteins and, further, that 

 both the a- and ^-configurations can be 

 demonstrated in unstretched and stretched 

 fibrillar preparations. Astbury and Saha 

 (1953) refer to these bacterial flagella as 

 "monomolecular muscles." 



It is to be stressed that the longitudinal 

 filaments of spermatozoa show no consistent 

 cross-striation or periodicity which might 

 be compared with that of the striated mus- 

 cle fibril (Bishop, 1961). In human sperm 

 prepared for electron micrography, Schultz- 

 Larsen (1958) found an indication of peri- 

 odicity with intervals of about 20 A, but 

 this phenomenon is irregular and remains 

 to l)e confirmed. Cross-striations at inter- 



vals of 500 to 700 A were found in Arbacia 

 sperm by Harvey and Anderson (1943), but 

 these have been interpreted as aggregation 

 artifacts rather than as true components of 

 structural periodicity. 



Whereas the physical basis for sperm mo- 

 tility is thus fairly well established in a con- 

 tractile protein system possibly associated 

 with the flagellar filaments, no fully satis- 

 factory theory of the operation of the mech- 

 anism has been advanced. The suggestion 

 of Bradfield (1955) that the cylindrically 

 arranged i^eripheral fibrils fire off progres- 

 sive contraction waves in successive order 

 was put forth hypothetically to describe a 

 plausible but untested description of flagel- 

 lation. Afzelius (1959) proposes, on the 

 basis of ultrastructural differences in mem- 

 bers of the pairs of peripheral fibrils, that 

 the mechanism may function along the lines 

 of the interdigitating-fibril scheme de- 

 scribed for striated muscle by Huxley and 

 Hanson (1954, 1957). Other more conserva- 

 tive speculations have been suggested (c/. 

 Bishop, 1958f; Gray, 1958; Nelson, 1959), 

 and final analysis of the precise nature of 

 the contraction-relaxation waves and their 

 synchronous operation in the sperm flagel- 

 lum must await further experimental inno- 

 vation and investigation. A striking gap 

 currently persists between the ultrastruc- 

 tural interpretations of spermatozoa and 

 the molecular characteristics associated 

 with motility. 



X. Fertilizing Capacity of Treated 

 Spermatozoa 



A wide range of environmental factors 

 has been employed in the study of mam- 

 malian sperm responses, dating from the 

 very earliest investigations of the gametes 

 (van Leeuwenhoek, 1678). Three principal 

 criteria have served as end points in the in- 

 vestigations of sperm physiology — motility, 

 metabolism, and fertilizing capacity. Inter- 

 related and interdependent in vivo, any of 

 these properties alone or in combination can 

 be assessed following experimental manipu- 

 lation of the sperm in vitro. The chemical 

 factors known to modify motility and meta- 

 bolic behavior of sperm may be arbitrar- 

 ily grouped roughly as follows: electrolytes 

 including the hydrogen ion, enzymatic in- 

 hibitors, chelating compounds, and a variety 



