330 ERWIN CHARGAFF 



spermatozoa,'"* "^'^^^ offer no particular difficulties of isolation, except for 

 the occasional need of 2 or 3 M NaCl solutions for the extraction of the 

 nucleoprotein,'"'*"^ the preparation of the intact deoxy pentose nucleic acids 

 of mammalian sperm often is no easy task. In what appears to be the first 

 isolation of deoxypentose nucleic acid from human sperm'" it was necessary 

 to treat the washed and defatted spermatozoa with crystalline trypsin 

 (free of deoxyribonuclease) before the extraction of nucleic acid could be 

 performed. In this manner, specimens of a high degree of polymerization 

 were obtained. In later experiments with ram and bull sperm a rather 

 unsatisfactory expedient, viz., extraction with KOH, seems to have been 

 employed. '2''^* It is known that even very strong salt solutions fail to 

 extract nucleoproteins from mammalian spermatozoa;'" but whether this 

 failure is due to unusual properties of the nucleoproteins themselves or to 

 obstruction by another protein that is removed by tryptic digestion'^^ 

 cannot be decided. 



Our information on deoxypentose nucleic acids from plant tissues is 

 regrettably meager. It is almost entirely limited to a few preparations from 

 several varieties of plant germ which since the pioneering experiments of 

 Kiesel and Belozersky'^^ and the later studies of Feulgen et a/.'-^ have been 

 known as good sources. Belozerskii and his colleagues''""'^^ have been 

 particularly interested in the isolation of nucleoproteins, mostly mixtures 

 of the deoxypentose and pentose varieties, from plant sources. The con- 

 tamination with pentose nucleic acid of the deoxypentose nucleic acid 

 specimens isolated in the recent past from wheat or rye germ"^"^'^'"'"* 

 is an obstacle to structural and analytical studies which appears to have 

 been overcome only rarely, either by degradation with alkali'-' or by 

 special purification"* (see Section III. 2. A. below). 



g. Nucleic Acids of Microorganisms and Viruses 



Unicellular organisms present a special problem as regards the isolation 

 of deoxypentose nucleic acids. No systematic treatment of preparative 



'" S. Zamenhof, L. B. Shettles, and E. Chargaflf, Nature 165, 756 (1950). 



126 x. Mann, in The biochemistry of fertilization and the gametes, Biochem. Soc. 



Symposia (Cambridge, Engl.) No. 7, 11 (1951). 

 '" L. E. Thomas and D. T. Mayer, Science 110, 393 (1949). 

 128 A. Kiesel and A. N. Belozersky, Z. physiol.Chem. 229, 160 (1934). 

 1" R. Feulgen, M. Behrens, and S. Mahdihassan, Z. physiol. Chem. 246, 203 (1937). 

 "" A. N. Belozerskii and 1. 1. Dubrovskaya, Biokhimiya 1, 665 (1936) ; Chem. Ahstr. 31, 



3100 (1937). 

 "' A. N. Belozerskii and L. A. Chernomordikova, Biokhimiya 5, 133 (1940); Chem. 



Ahstr. 35, 1457 (1941). 

 "2 A. N. Belozerskii and M. S. Uspenskaya, Biokhimiya 7, 155 (1942); Chem. Abstr. 



38, 131 (1944). 

 '" S. Laland, W. G. Overend, and M. Webb, Acta. Chem. Scand. 4, 885 (1950). 

 "< G. Brawerman and E. Chargaflf, J. Am. Chem. Soc. 73, 4052 (1951). 



