ENZYMES ATTACKING NUCLEIC ACIDS 589 



erylphosphorylcholine, and glycerylphosphorylethanolamine are hydro- 

 lyzed by homogenates and crude autolysates of intestinal mucosa of calves, 

 but not by highly purified intestinal phosphatase.^^ 



Highly polymerized DNA is likewise resistant toward purified intestinal 

 phosphatase/^' ^^ but digests of DNA obtained by incubation with deoxy- 

 ribonuclease I are rapidly and completely hydrolyzed to nucleosides and 

 inorganic phosphate. 



Yeast and pancreas PNA are completely cleaved to nucleosides and ortho- 

 phosphate by highly purified intestinal phosphodiesterase provided the 

 incubation is carried out with relatively large amounts of the enzyme. The 

 rates of hydrolysis of DNA polynucleotides by intestinal phosphatase are 

 considerably higher than those of PNA.^*- 



The hydrolysis of phosphomonoesters by intestinal phosphatase proceeds 

 much more rapidly than that of polynucleotides; since the latter is thus the 

 limiting factor, mononucleotides are usually not detectable in the digests. 

 Klein and Thannhauser^^^ found, however, that the phosphomonoesterase 

 activity of intestinal mucosa is inhibited by arsenate to a higher degree than 

 is its phosphodiesterase action. In the presence of arsenate, appreciable 

 amounts of mononucleotides accumulate in the digests. The amounts of 

 deoxymononucleotides in arsenate-containing digests of depolymerized 

 DNA are sufficient to permit their isolation by fractionation procedures. 

 The presence of mononucleotides in PNA hydrolysates obtained with 

 intestinal phosphatase in the presence of arsenate was demonstrated by 

 Cohn and Volkin by means of ion-exchange chromatography. "''■^^^ In con- 

 trast to pancreas ribonuclease I, which forms only 3'-pyrimidine nucleo- 

 tides, the nucleotides originating from the action of intestinal phosphatase 

 are 5'-purine and pyrimidine nucleotides. 



The strong nucleophosphodiesterase activity of intestinal phosphatase 

 raises the ciuestion as to whether alkaline phosphatases of other tissues 

 are likewise capable of hydrolyzing certain phosphodiester linkages. So far, 

 the alkaline phosphatases in various tissues have been considered as identi- 

 cal although GuUand"^ considered alkaline bone phosphatase as a strict 

 phosphomonoesterase. On the strength of Gulland's interpretation, this 

 enzyme has recently been used as a reagent for terminal secondary phos- 

 phoryl groups of nucleic acids. '^^ The author of this review, however, is not 

 convinced of the evidence in favor of the exclusive monophosphoesterase 

 nature of bone phosphatase. Gulland's view was based on experiments with 



1" W. Klein, Z. physwl. Chem. 207, 164 (1933). 



>" W. Klein and S. J. Thannhauser, Z. physiol. Chem. 218, 164 (1933). 



1^^ W. E. Cohn, D. G. Doherty, and E. Volkin in "Phosphorus Metabolism" (McElroy 



and Glass, eds.), Vol. 2, p. 339. Johns Hopkins Press, Baltimore, 1952. 

 '« J. M. Gulland and E. M. Jackson, /. Chem. Soc. 1938, 1492. 



