ENZYMES ATTACKING NUCLEIC ACIDS 625 



with a single optimum at pH 7.8. Miller and Kozloff-^^ demonstrated the 

 presence of ribonuclease activity in the nuclear fraction of chicken erythro- 

 cytes obtained by saponin hemolysis. These authors believ^e that the ribo- 

 nuclease activity of the nuclei is localized in the nuclear membrane since 

 it is not increased by freezing and thawing of the enzyme preparation. 



3. Intracellular Localization of Deoxyribonuclease I and 

 Ribonuclease I in Pancreas 



The crystallized ribo- and deoxyribonucleases of the pancreas offer the 

 experimental advantage that specific antibiodies for these two enzymes can 

 be prepared. Such antibodies were used by Marshall for studies on the intra- 

 cellular distribution of ribonuclease I and deoxyribonuclease I by histo- 

 chemical application of the specific antibodies labelled with fluores- 

 cein.-^'*-*^ Ribonuclease I and deoxyribonuclease I were found in the 

 zymogen granules and in the cytoplasm, but not in mitochondria and nu- 

 clei. Schneider and Hogeboom-" found ribo- and deoxyribonuclease activity 

 in liver mitochondria. Probably the mitochondrial nucleases are not identi- 

 cal with the crystallized enzymes of pancreas. 



4. Other Enzymes of Nucleic Acid Metabolism 



According to Stern et al.,^^^ adenosine deaminase, guanase, and nucleoside 

 phosphorylase are present in high concentrations in nuclei of many tissues, 

 whereas nucleotide phosphatases and uricase are present only in relatively 

 small amounts if at all. This question is discussed further in Chapters 18 

 and 21. 



XI. Addendum 



{Concerning the Enzymic Formation of Nucleoside Di- and Triphosphates) 



When the organization of Chapter 15 was undertaken it was decided to 

 exclude enzyme reactions involving the pyrophosphoryl groups of nucle- 

 oside polyphosphates since their discussion seemed to be pertinent to the 

 field of energy metabolism rather than to that of nucleic acids. During the 

 last year, however, the presence of polyphosphates of various ribonucleo- 

 sides in animal tissues was demonstrated by Schmitz, Hurlbert and Potter.^" 

 All these compounds are phosphorylated in their 5'-positions. Conceiv- 



283 Z. B. Miller and L. M. Kozloff, J. Biol. Chem. 170, 105, (1947). 

 28" J. M. Marshall, Exptl. Cell Research 6, 240 (1954). 



285 A. H. Coons, H. J. Creech, R. N. Jones, and E. Berliner, J. Immunol. 45, 159 

 (1942). 



286 H. Stern, V. G. Allfrey, A. E. Mirsky, and H. Laetren, J. Gen. Phijsiol. 35, 559 

 (1952). 



287 H. Schmitz, R. B. Hurlbert, and V. R. Potter, /. Biol. Chem. 209, 41 (1954). 



