enzymes attacking nucleic acids 591 



2. Specific Nucleotide Phosphatases (Nucleotidases) 

 a. 5' -N iicleotidases 



The existence of specific phosphatases for the hydrolysis of 5'-nucleotides 

 was implicitly suggested by the old observation that mammalian skeletal 

 muscle and heart tissue which do not hydrolyze glycerophosphate, 2'- and 

 3'-nucleotides, and many other monoesters of phosphoric ac^d, are capable 

 of hydrolyzing 5'-adenylic and 5'-inosinic acids. Reis^'*^"^''* established in 

 systematic studies the widespread occurrence in mammalian tissues of a 

 specific 5'-nucleotidase which is particularly abundant in muscle and nerve 

 tissue and in bull testicle. ^^^ In these tissues, the largest part of the enzyme 

 is closely associated with the insoluble particles. 



In the cytoplasm and the nuclei of the cells of smooth muscle (such as 

 uterus and aorta) and in fibroblasts, the presence of a specific 5'-nucleo- 

 tidase was demonstrated histochemically by Wachstein and Meisel.^^^ Par- 

 ticularly high concentrations of o'-nucleotidase were found histochemically 

 in the posterior lobe of the human pituitary gland. ^^^ 



Soluble 5'-nucleotidases of strong activity were found in snake venoms. 

 In the plant kingdom, potatoes are a convenient source for the preparation 

 of purified extracts with highl}^ specific 5'-nucleotidase activity. ^^- The 

 (juestion as to whether the 5'-imcleotidases obtained from the various 

 sources are closely related in regard to their chemical properties or not, can- 

 not be decided at present because the purification procedures of these en- 

 zymes were designed for the purpose of obtaining preparations with high 

 enzymic specificity rather than homogeneous enzyme proteins. 



Properties of 5' -Nucleotidase of Bull Semen. Some of the properties of 

 5'-nucleotidase from bull semen, which was studied by Heppel and Hil- 

 moe,^^^ are as follows. 



pH Optimum. Seminal 5'-nucleotidase has its optimal activity at pH 

 8.5; 5'-nucleotidases from other sources have likewise a pH optimum in this 

 region. 



Potency. The activity per milligram of the most highly purified prepara- 

 tions of seminal 5'-nucleotidase is about twice that of purified intestinal 

 phosphatase. The concentration of the enzymic activity in seminal plasma 

 is much higher than that of intestinal phosphatase in the intestinal mucosa. 



1" J. Reis, Bull. sue. chim. biol. 22, 36 (1934). 



1" J. Reis, Enzymologia 2, 183 (1937). 



"8 J. Reis, Enzymologia 5, 251 (1938). 



1" T. Mann, Biochem. J. 39, 451 (1945). 



150 M Wachstein and E. Meisel, Science 115, 652 (1952). 



^" A. G. E. Pearse and J. L. Reis, Biochem. ./. 50, 534 (1952). 



162 A. Kornberg and W. E. Pricer, Jr., J. Biol. Chem. 186, 557 (1950). 



>" L. A. Heppel and R. J. Hilmoe, J. Biol. Chem. 188, 665 (1951). 



