RESPIRATION AND OXIDATIVE PHOSPHORYLATION 113 



concentration are four to ten times larger than those reported else- 

 where. In beef liver mitochondria, for example, Estabrook and 

 Holowinsky (1961) obtained a figure of 0.1 to 0.5 mM for the con- 

 centration of all cytochromes along with flavoprotein. With an ultra- 

 sensitive spectrophotometer focused on a single cell Perry et al. 

 (1959) found a total concentration of 0.14 mM in the giant mito- 

 chondrion or Xebenkern of the grasshopper spermatid. Two ex- 

 planations can be offered for the apparent discrepancy with our re- 

 sults; either the cytochromes are located at sites other than the 

 middle piece, or the mitochondrion of the mature spermatozoon 

 is more condensed and has a higher internal concentration of en- 

 zymes than that of immature germ cells. Indeed, Xebenkern shrink- 

 age is in fact very likely as the cell passes from spermatid to mature 

 spermatozoa stages. 



These results suggest that a more significant figure would be the 

 number of cytochrome molecules per cell in relation to cell dimen- 

 sion, nitrogen content, or dry weight. Thus, the mature germ cells 

 of the grasshopper and bull have about the same dimensions and, con- 

 sidering a Xebenkern of 30 ^. 3 , calculations from the data of Perry 

 et al. (1959) give a value of 2.5 X 10 6 molecules of all cytochromes 

 per cell, as compared with 2.9 X 10° found here for bull sperm. 

 Humphrey (1950) gave a value of 1 mg dry weight per 10 s oyster 

 spermatozoa, the comparable value being 3 mg for bull sperm. By 

 multiplying the figure 0.8 X 10 (i molecules per cell found in Spisula 

 sperm by this factor, 3, one obtains 2.4 X 10 6 molecules per cell, again 

 close to the figure for bull spermatozoa. It may be concluded, there- 

 fore, that the spermatozoa examined thus far carry equivalent quan- 

 tities of cytochromes, namely about 2.5 X 10 6 molecules in each cell. 



The above data indicate that while the relative proportion of cyto- 

 chromes may differ significantly, no striking difference exists in 

 either concentration or turnover number of the respiratory pig- 

 ments of the two mammalian and one invertebrate species of sperm 

 investigated here. 



Function of Respiratory Enzymes 



The response of the respiratory pigments to oxidizable substrates 

 such as lactate or succinate has been studied on bull spermatozoa. A 

 high positive effect of 20 mM lactate is observed on respiration of 



