Protein Constituents and Enzymes of Seminal Plasma 123 



remaining two ATP-ases, designated respectively as 'acid' and 

 'alkaline', produce orthophosphate; the 'acid' ATP-ase has a pH 

 optimum at 5-7-60, requires magnesium, is inhibited by calcium, 

 and can be inactivated completely by heating for 20 min. at 60°; it 

 does not act on i5-phosphoglycerol; the 'alkaline' ATP-ase is more 

 heat-resistant, has a pH optimum at 8 -4-8 -8, and is stimulated by 

 calcium and also by magnesium. Both these enzymes are active not 

 only tov^ards adenosine triphosphate but adenosine diphosphate 

 as v^ell. 



Bull seminal plasma contains in 1 ml. about 80 units of acid 

 ATP-ase, 130 units of alkaline ATP-ase, 40 units of the pyrophos- 

 phate-forming ATP-ase, and 2900 units of 5-nucleotidase. It re- 

 mains for future studies to define the physiological significance 

 of all these enzymes, particularly the 5-nucleotidase which is so 

 characteristic of semen. Possibly, there is some link between them 

 and other nucleolytic enzymes and they may well play a role in the 

 metabolism of purine compounds in semen and reproductive organs. 

 The occurrence of nucleases in human and sea-urchin semen 

 (Zamenhof, Shettles and Chargaff, 1950; Mazia, 1949), the cozy- 

 mase-destroying activity of bull seminal plasma (Mann, 1945a), the 

 interesting findings on the presence of uric acid in bull semen 

 (Barron and Haq, 1948; Leone, 1952), and the more recent demon- 

 stration of xanthine oxidase in the bull vesicular secretion (Leone, 

 1953), are but a few examples of problems in this field, which await 

 further and more detailed study. 



