BIOLOGY OF SPERMATOZOA 



759 



It seems that, although there may exist 

 some variation in the ability of invertebrate 

 sperm to withstand anaerobiosis or to utilize 

 glycolytic substrates to a limited extent, 

 these cells generally are dependent on re- 

 spiratory i)rocesses for the major produc- 

 tion of chemical energy. Since the conditions 

 of external fertilization deny them ready 

 access to glycolytic substrates in the en- 

 vironmental milieu, the sperm have failed 

 to develop, or have secondarily lost, their 

 glycolytic capacity, so characteristic of 

 mammalian and avian spermatozoa. It is 

 unlikely, although, of course, possible, that 

 failure to utilize hexoses rests on the im- 

 permeability of the sperm to these sub- 

 strates. 



C. MAMMALIAN SPERM METABOLISM 



As is the case with invertebrate sperma- 

 tozoa, most of wdiat is known about the 

 biochemical characteristics of mammalian 

 sperm has been acquired from studies, in 

 vitro. To the extent that experimental con- 

 ditions may duplicate those within the 

 genital tract, the behavior of sperm, in vivo, 

 can only be surmised. Considerable varia- 

 tion is seemingly inherent in the metabolic 

 characteristics of sperm of different species 

 and in the gametes removed from different 

 levels of the tract (see Dott, 1959). There 

 is little doubt that such variation exists, but 

 the causes may not be so distinctive as is 

 generally claimed. Discounting differences 

 in sperm behavior attributable to variations 

 in handling and experimental procedure, it 

 seems likely, without implying fundamental 

 differences in metabolic patterns, that 

 sperm, like most other types of cells, possess 

 a lability of subcellular activity which en- 

 ables them to regulate to external and in- 

 trinsic factors. The variations in sperm be- 

 havior, which at times seem so unique, are 

 not likely to conflict with the conservative 

 concept of the ''biochemical unity of living 

 matter" (Fruton and Simmonds, 1959) . 



The principal metabolic characteristics of 

 mammalian spermatozoa have been ex- 

 tensively reviewed by Mann (1949, 1954) ; 

 elsewhere special attention has been paid 

 to human sperm (MacLeod, 1943b; Ivanov, 

 1945; Westgren, 1946; Lundquist, 1949). 

 It is now well established that both glyco- 



lytic and oxidative processes provide energy 

 for mammalian sperm and either one or 

 both types of metabolic pattern can serve 

 the sperm after insemination into the fe- 

 male genital tract. Motility of ram and 

 bull sperm, in vitro, is enhanced by the 

 presence of both hexose and oxygen to- 

 gether (Walton and Dott, 1956). Whereas 

 fructose is the common natural substrate 

 at ejaculation (see chapter by Price and 

 Williams-Ashman), most mammalian sperm 

 also utilize glucose and mannose with equal 

 or greater facility (Mann, 1954). The j)rin- 

 cipal steps in the degradation of sperm 

 hexose to lactic acid occur by the well 

 known Embden-Meyerhof scheme involving 

 ATP as phosphate donor and diphospho- 

 pyridine nucleotide (DPN) as hydrogen 

 carrier (electron transport system) ; this 

 has been demonstrated in both ram and bull 

 sperm, mainly by the identification of in- 

 dividual enzyme systems and glycolytic in- 

 termediates (Mann, 1954). The several 

 components of the cytochrome-cytochrome 

 oxidase electron transport system have been 

 established by manometric and spectropho- 

 tometric methods in a variety of sperma- 

 tozoa, including those of man (MacLeod, 

 1943a; Mann, 1951a). Less direct, but 

 nevertheless adequate, evidence further in- 

 dicates that the Krebs tricarboxylic acid 

 cycle is involved in the oxidative processes 

 (Mann, 1954; White, 1958). Indeed, there 

 is no evidence to suggest that the over-all 

 metabolic systems of sperm, at least of the 

 ram and bull, are significantly different 

 from those of muscle or of most other mam- 

 malian tissues. The rates of glycolysis and 

 oxidation vary, but the mechanisms are 

 basically the same. Moreover, it is probable 

 that under many conditions, in vivo, there 

 is considerable interaction between the gly- 

 colytic and oxidative processes (for general 

 discussion, see Packer, 1959; Packer and 

 Gatt, 1959). Both types of metabolic path- 

 ways, glycolytic and oxidative, are com- 

 plete within the sperm flagellum. This is 

 clear from the fact that in both the guinea 

 pig (Cody, 1925) and bull (Mann, 1958) 

 cases have been reported in which the fia- 

 gella are naturally separated from the heads 

 at the time of ejaculation; such flagella are 

 actively motile and show high rates of lac- 



