Gametogenesis, Fertilization and Parthenogenesis 



183 



These findings can account in large part for 

 the "dilution effect." The proteins of the 

 seminal plasma can also bind heavy metals. 

 Since such protein wovild be present in 

 higher concentration the less the semen is 

 diluted, the spermatozoa in denser suspen- 

 sions would be protected from the toxic ac- 

 tion of the trace metals. This is consistent 

 with the favorable action of seminal plasma 

 found by Gray ('28) and Hayashi ('45). 



Another interesting effect of the amino 

 acids and other metal-chelating agents is 



fluid. Motility is maintained under anaerobic 

 conditions in the presence of glycolyzable 

 substrates. Mann ('46, '49) has recently 

 identified the normal substrate in seminal 

 fluid as fructose. The work of Mann ('45a, b, 

 '49), Lardy and Philips ('41-'45), MacLeod 

 ('39-46) and others has shown that the 

 glycolysis in sperm is essentially the same 

 as in other animal tissues and in yeast 

 (phosphorylation of the sugar by adenosine 

 triphosphate in the presence of hexokinase 

 to hexosemonophosphate, then hexose di- 



TIME (MIN.) 

 Fig. 55. Photo-reversible inhibition by carbon monoxide of the respiration of sperm of the sea urchin 

 Echinus esculentus. Gas mixture, 90% CO and 10% O2; dark periods, to 30 and 60 to 90 minutes; light 

 periods (700 watt lamp), 30 to 60 and 90 to 120 minutes; temperature, 15:1° C; sperm suspension, 4.4 X 

 108 per ml. Broken line shows average rate of O2 consumption per hour. (From Rothschild, '48a.) 



their ability to enable the sperm to induce 

 a good fertilization-reaction under condi- 

 tions in which the sperm, diluted and aged 

 in ordinary sea water, call forth poor mem- 

 brane elevation (Tyler and Atkinson, '50; 

 Tyler, '53). The results demonstrate that the 

 type of response given by the egg can be 

 determined by the vitality of the inseminat- 

 ing sperm. The spermatozoon evidently does 

 not act simply in "all or none" manner in 

 the sense of operating a trigger mechanism 

 in the egg. 



Investigation of the substrate that is 

 normally utilized by the sperm and the enzy- 

 matic pathways through which it is metabo- 

 lized has been confined mainly to mam- 

 malian spermatozoa. It is now well established 

 that mammalian sperm have a predom- 

 inantly glycolytic metabolism even un- 

 der aerobic conditions and that the substrate 

 is a reducing sugar present in the seminal 



phosphate, and breakdown through triose- 

 phosphate, phosphoglyceric acid and pyruvic 

 acid to lactic acid; with resynthesis of ATP 

 by transfer of phosphate from phosphogly- 

 ceric acid to adenylic acid or reaction be- 

 tween inorganic phosphate and adenylic acid 

 catalyzed by cozymase). Aerobically in the 

 absence of external glycolyzable substrate 

 the spermatozoa apparently oxidize phos- 

 pholipid. The mammalian sperm have been 

 found to contain all the enzymes involved 

 in the Krebs' cycle, as well as the cyto- 

 chromes a, h, and c and cytochrome oxidase. 

 However, under aerobic conditions motility is 

 relatively quickly lost even in the presence 

 of glycolyzable substrate. This has been at- 

 tributed by MacLeod ('46a) to the produc- 

 tion of hydrogen peroxide, which he believes 

 may reach sufficient concentration to kill the 

 sperm. Addition of substances containing 

 catalase was found to retard the aerobic 



