ISOLATION AND COMPOSITION OF DEOXYPENTOSE NUCLEIC ACIDS 321 



serum albumin,*^"*'* and with many other proteins*"'*^'** were studied. One 

 of the most striking differences between a nucleoprotamine or a nucleo- 

 histone on the one hand and artifacts prepared by the mixing of a nucleic 

 acid and a basic protein on the other is the solubiUty of the first-mentioned 

 complexes in the absence of electrolytes. It now appears that it is possible 

 to prepare nucleic acid - protamine compounds of similar solubility in 

 water when very dilute aqueous solutions of the components are brought 

 together.'^ The combination of deoxypentose nucleic acid with enzymes has 

 been studied in several instances.*^ '^^ Of particular interest is a recent 

 investigation of Shapot" dealing with the formation of a complex between 

 deoxyribonucleic acid and pancreatic deoxyribonuclease which is stable in 

 the absence of Mg++ ions.^*'' Attention may also be drawn to studies on 

 the protection against heat coagulation that the presence of nucleic acid 

 confers on proteins. ^^ '^^ 



III. Isolation of Deoxypentose Nucleic Acids 



1. General 



The isolation of a cellular constituent of high molecular weight and 

 complex structure poses several problems of which the most important is 

 the decision whether the isolated preparation may still be regarded as 

 representative of the state in which it occurred in the living cell. Strictly 

 speaking, no compound, once it is isolated from the cell, can be considered 

 as native. When a pillar is hacked out of a building, neither pillar nor 

 building is left. If the nucleic acids occur in the cell in combination with 



'* P. Alexander, Biochim. et Biophys Acta. 10, 595 (1953). 



" K. B. Bjornesjo and T. Teorell, Arkiv. Kemi, Mineral. Geol. 19A, No. 34 (1945). 



8" O. P. Chepinoga and R. Sh. Grosblat, Ukrain. Biokhim. Zhur. 21, 121 (1949) ; Chem. 

 ^6s/r. 48, 4014 (1954). 



8' J. P. Greenstein and M. L. Hoyer, J. Biol. Chem. 182, 457 (1950). 



82 E. Stenhagen and T. Teorell, Trans. Faraday Soc. 35, 743 (1939). 



w E. Goldwasser and F. W. Putnam, J. Phys. & Colloid Chem. 54, 79 (1950). 



»* E. P. Geiduschek and P. Doty, Biochim. et Biophys. Ada 9, 609 (1952). 



"5 A. N. Belozeiskii and G. D. Bazhilina, Biokhimiya 9, 134 (1944) ; Chem. Abstr. 39, 

 314 (1945). 



»« P. Ohlmeyer, Biochim. el Biophys. Acta 4, 229 (1950). 



" V. S. Shapot, Biokhimiya 17, 299 (1952) ; Chem. Abstr. 46, 10238 (1952). 



88 V. L. Ryzhkov and G. I. Loidina, Doklady Akad. Nauk S.S.S.R. 86, 181 (1952); 

 Chem. Abstr. 47, 1243 (1953). 



88a The spectral shift in the e.xtinction maximum from 260 to 254 m>t is, according to 

 unpublished experiments with Mr. H. S. Shapiro, not attributable to the formation 

 of the enzyme-substrate complex, as was thought by Shapot. 8' An identical spec- 

 trum can be reconstructed by the summation of the individual spectra of deoxy- 

 ribonucleic acid and deoxyribonuclease, when measured at the pH at which the 

 complex is examined. 



8« C. E. Carter and J. P. Greenstein, J. Natl. Cancer Inst. 6, 219 (1946). 



