RESPIRATION AND OXIDATIVE PHOSPHORYLATION 129 



mitochondria as might be expected in such a compact cell. Calcula- 

 tion of the number of enzyme molecules per spermatozoon yields 

 strikingly similar values for Spisula and bull gametes, despite im- 

 portant ecological differences between these spermatozoa. The ac- 

 tivity of individual cytochromes, when defined by turnover num- 

 bers, are all within the same range and are comparable to values 

 found with tissue mitochondria, ascites cells, and other biological 

 preparations. A singular feature noted in spermatozoa of the dog 

 and bull is the high relative content of cytochrome oxidase; this char- 

 acteristic remains to be explained. 



The active participation of these enzymes has been demonstrated 

 during oxidation of lactic or succinic acid in bull spermatozoa. The 

 respiratory chain offers no abnormal feature, responds to respiratory 

 inhibitors such as Amytal and antimycin A with crossover phenom- 

 ena which could be expected. Azide plays a complex role in sperma- 

 tozoa, acting specifically on cytochrome oxidase, an effect currently 

 associated with that inhibitor, but also possessing uncoupling action 

 and possibly exerting an inhibition on glycolysis as well. The last 

 two effects are primarily involved in the suppression of motility by 

 azide. Such effects have either been observed or suggested in the 

 course of other investigations bearing on different biological ma- 

 terials. 



The important difference to be noted is in the response of sperma- 

 tozoa from Spisula and dog or bull to an uncoupling agent, the 

 spermatozoa of the invertebrate being much more sensitive. The 

 effect of dinitrophenol on respiration is six times greater in Spisula 

 than in dog sperm, and motility can be completely abolished in the 

 former but not in the latter. Experiments with Amytal also show 

 that in dog sperm, respiration and motility decrease in parallel, 

 whereas in Spisula full motility is maintained at 60% inhibition of 

 respiration. These results seeim to indicate that in dog spermatozoa, 

 conservation of energy associated with electron transfer is of less 

 efficiency than that in Spisula gametes. Despite the capacity of oxi- 

 dative enzymes to support motility and the higher theoretical yield 

 associated with their activity, spermatozoa of mammals use glycolysis 

 preferentially even in the presence of oxygen. An hypothesis to ac- 

 count for this is that of compartmentalization within the cell. Energy 

 equivalents which appear through oxidative phosphorylation are 



