BIOLOGY OF SPERMATOZOA 



757 



(Mann, 1954). Rothschild (1959) investi- 

 gated the anaerobic heat production in buff- 

 ered suspensions of bull semen under vari- 

 ous anisotonic conditions and found that an 

 initial shock reaction, marked by reduced 

 heat production and metabolic activity, 

 was followed by gradual recovery or adap- 

 tation which in some cases was complete. 

 Such adaptation seems particularly charac- 

 teristic of bull sperm but the nature of the 

 osmotic regulation is not entirely clear. 

 Under severely unfavorable conditions the 

 ])ermeability of ram and bull sperm is so 

 altered as to permit the apparent leakage 

 of large molecules such as cytochrome c 

 (Mann, 1951a, 1954). Pronounced changes 

 in permeal)ility accompany the phenomenon 

 known as "cold-shock" (Mann and Lutwak- 

 Mann, 1955). 



Chemical analyses of ram and bull sperm 

 by Green (1940), Zittle and O'Dell (1941), 

 and others indicate that the surface mem- 

 brane contains lipid, probably bound as 

 phosjiholipoprotein; the lipid-free mem- 

 l)rane is high in nitrogen and cystine and 

 bears a superficial resemblance to keratin 

 (Mann, 1954). The toughness and the elas- 

 tic properties of human sperm actually have 

 been ciualitatively determined by dexterous 

 microdissection technique (Moench, 1929). 



The sperm surface at physiologic ionic 

 strength and pH bears a negative charge 

 which has been claimed to be higher on the 

 tail than on the head (Joel, Katchalsky, 

 Kedem and Sternberg, 1951 ) . The gametes 

 thus tend to migrate electrophoretically to- 

 ward the anode. According to Machowka 

 and Schegaloff (1935), this movement is 

 counteracted, at certain field strengths, by 

 a galvanotropic tendency to swim actively 

 toward the cathode. The negative charge on 

 the sperm surface may be attributable to 

 phosphate, carboxyl, and/or sulfate groups 

 attached to organic components of the 

 membrane. 



Several attempts have been made to uti- 

 lize the electrophoretic properties of sperm 

 in order to separate X- and Y-bearing 

 gametes. Schroder (1940a, b, 1941a, b, 1944) , 

 in an interesting and apparently careful 

 series of investigations, claimed to have ac- 

 complished this with rabbit sperm ; the two 

 types of gametes thus separated, when arti- 



ficially inseminated into does, gave pre- 

 dominantly (78 to 80 per cent) male or fe- 

 male offspring. More recent work by Gordon 

 (1957) suggests concurrence in these find- 

 ings, but both the technicjue employed and 

 the conclusions derived indicate the need for 

 further confirmation. If such electrophoretic 

 separation of the two cytogenetically dis- 

 tinct types of sperm is possible, it would 

 be of interest to ascertain the reason for the 

 behavior, whether, for example, the male- 

 and female-producing gametes carry dif- 

 ferent ^-i:)otentials or otherwise vary in sur- 

 face composition. Schroder's studies did 

 indeed indicate that the electrophoretic re- 

 sponse might be attributable to differences 

 in the comjionents of the lipoprotein sheaths 

 of the two tyi)es of spermatozoa. 



VIII. Sperm Metabolism 



A. SOURCES OF ENERGY 



In biochemical investigations of sperma- 

 tozoa the focus of attention has been on the 

 metabolic processes associated with the pro- 

 duction of chemical energy required for 

 motility. Although the sperm of relatively 

 few species have been extensively explored, 

 a fairly consistent pattern of metabolic ac- 

 tivities has been established. Mammalian 

 sperm, in general, display extensive gly- 

 colytic activity under both aerobic and an- 

 aerobic conditions, and carry on oxidative 

 respiration when conditions are appropriate 

 (Mann, 1954). Invertebrate spermatozoa, 

 on the other hand, rely almost entirely on 

 oxidative processes and show little, if any, 

 glycolysis (Rothschild, 1951a). Regardless, 

 however, of the nature of the substrate and 

 the pattern of metabolism, the importance 

 of the chemical conversions lies in the 

 coupling of these exergonic reactions with 

 the synthesis of ATP as a utilizable source 

 of chemical energy for the performance of 

 work (Lardy, Hansen and Phillips, 1945; 

 Lehninger, 1955, 1959). In active sperma- 

 tozoa much of this energy source is consumed 

 by the processes underlying motility ; an un- 

 known fraction may be utilized in other ac- 

 tivities, including possible synthetic proc- 

 esses, conduction, and membrane transport. 



In mammalian spermatozoa, anaerobic 

 glycolysis supplies sufficient ATP energy to 



