90 The Biochemistry of Semen 



Sea-urchin semen has approximately the same concentration 

 of copper as ram semen, with a similar distribution of the metal 

 between sperm and seminal plasma (Barnes and Rothschild, 1950). 



Cytochrome 



Early investigators of semen were well aware of the fact that 

 spermatozoa give a positive indophenol reaction with the 'Nadi* 

 reagent, particularly marked in the regions of the acrosome and 

 middle-piece (Herwerden, 1913). Ostwald (1907), Voss (1922) and 

 Sereni (1929), among others, made important contributions to the 

 subject of sperm indophenol oxidase and noted that the intensity of 

 the reaction increased towards the final stages of sperm maturation 

 and after ejaculation. 



When in 1925 Keilin discovered cytochrome and identified 

 indophenol oxidase with cytochrome oxidase, he noticed that of all 

 the organs of a perfused frog, the heart muscle and the testicular 

 tissue exhibited the strongest absorption spectrum of cytochrome. 

 A little later, Brachet (1934) reported the presence of cytochrome in 

 frog sperm, and Ball and Meyerhof (1940) in sea-urchin spermatozoa. 

 In spite of that, attempts by several workers to detect the spectrum 

 of cytochrome in mammalian spermatozoa met with failure and the 

 functioning of cytochrome in mammalian semen continued to be 

 deduced only indirectly from the evidence based on the oxidation 

 of succinate and phenylenediamine (Shergin, 1940; Lardy and 

 Phillips, 1941c; Zittle and Zitin, 1942^; MacLeod, 1943a). This led 

 to some speculation, particularly in the case of human semen, about 

 the mechanism of respiration, the more so, since it has been asserted 

 that the oxygen consumption of human semen is associated pre- 

 dominantly with the seminal plasma and not with the spermatozoa 

 themselves (MacLeod, 1941a; Ross, Miller and Kurzrok, 1941; 

 Zeller, 1941). 



In an efTor^ to re-examine the whole problem, the author made a 

 study of the cytochrome content of mammalian spermatozoa (Mann, 

 1945a, c). With the aid of the microspectroscope, an instrument 

 eminently suitable for direct observation of absorption bands in 

 tissues, no difficulty was experienced in the detection of the com- 

 plete cytochrome spectrum in both ram and bull semen. Human 

 semen has a sperm density at least ten times lower than bull semen, 



