288 DAVID W. BISHOP 



into the principal segment of the tail (Rothschild, 1955). But in spe- 

 cies like the sea urchin, clam, and mammals generally, there is little 

 evidence that mitochondria are present outside the midpiece. It is 

 not likely either that these two enzymes constitute part of an extra- 

 mitochondrial respiratory system in the flagellum, particularly if the 

 above-noted permeability data of Steinbach and Dunham find wide 

 application (see also Gonse, this symposium). We feel rather con- 

 fident that the energy for motility, in invertebrate sperm at least, 

 comes from oxidative phosphorylation, and Rothschild and Cleland 

 (1952) have demonstrated that endogenous phospholipid, located al- 

 most entirely or exclusively in the midpiece, serves as energy sub- 

 strate. If for the moment just the invertebrate type is considered, we 

 seem to be faced with the paradox of having a sperm with mitochon- 

 dria and substrate limited to the midpiece while enzymes of the ter- 

 minal electron transport chain, and presumably the sites of energy 

 transfer as well, are distributed throughout the tail. 



The simple pumping of ATP into a motile system does not ex- 

 plain how the mechanism works, but there is little basis for the ar- 

 gument that this nucleotide does not in some way facilitate the 

 transfer of energy involved in chemomechanical coupling. Lord 

 Rothschild's evidence that total nucleotide (ATP, ADP, and AMP 

 + IMP) does not vary significantly during large changes in activity 

 of anaerobic suspensions of bull sperm might be anticipated whether 

 ^phosphorylation did or did not occur. The details of these experi- 

 ments should prove interesting. With respect to ATP levels alone, 

 even in a nonphosphorylating system, it is a well-known fact that 

 nucleotide changes are difficult to demonstrate with active muscle 

 preparations (see also Hayashi, this symposium). In this connection 

 it is worth calling attention to the conflicting evidence regarding the 

 occurrence of phosphagen and a transphosphorylating system in 

 sperm. The most recent study of mammalian spermatozoa indicates 

 their absence (White and Griffiths, 1958); in sea urchin gametes, 

 however, a CP reserve system is claimed to be present (Yanagisawa, 

 1959). If one assumes these findings are confirmed, dare one suggest 

 that the presence or absence of a phosphagen system in invertebrate 

 or mammalian sperm might reflect the marked metabolic differences 

 and their relative capacities for rapid rephosphorylation of ADP? 

 In light of the conclusion suggested in the ensuing paragraph, a 



