OPTICAL PROPERTIES OF NUCLEIC ACIDS 531 



comes from the analytical data of Vendrely and Vendrely," who find a constant DNA- 

 arginine ratio in the erythrocyte nuclei of many fish species which show large varia- 

 tions in DNA content. Some interesting observations on the composition and solu- 

 bilitj' of synthetic DNA-protamine complexes in relation to natural nuceloproteins 

 are discussed by Alexander." Stern'' has found that model polynucleotide and poly- 

 peptide chains can interlace without straining of bond angles to allow the formation 

 of salt linkages, as envisaged by Astbury, in such a waj- as to lock the polynucleotide 

 chain in a specific configuration. In this connection it should perhaps be noted that 

 free DNA preparations from different species show the same structure independent 

 of the base constitution.'* 



Riley and Arndt'* have concluded from quantitative X-ray scattering studies of 

 herring sperm and calf thymus nucleoproteins and of the constituent nucleic acids 

 and proteins (clupeine and histone, respectively) that a nucleoprotein is best regarded 

 as a fairly gross addition complex, presumably held together by salt linkages, rather 

 than an intimate and specific association of the two components, for example, a fully 

 extended /3-type polypeptide chain wound around the double-helix polynucleotide 

 chain, as envisaged by Watson and Crick." 



It is not yet possible, on the basis of these conflicting views on the nature of the 

 protein-nucleic acid association, to make any prediction about the additivity or 

 otherwise of the absorptivity contributions of the two components of a nucleoprotein. 

 Some experimental data are available. Shack and co-workers'"'^ find that the anom- 

 alous spectrophotometric titration of thymus DNA is also shown by the related 

 nucleohistone and by one isolated from a transplantable mouse lymphoma. They 

 conclude that the same alkali-labile hydrogen-bonded structure is present in a nucleo- 

 protein and the derived nucleic acid. 



Blout and Asadourian" have measured the absorbance of calf thymus DNA solu- 

 tions containing added protein differentially against control solutions of protein 

 and find that both lysozyme and bovine plasma albumin lower the DNA absorbance; 

 in the presence of sodium chloride, the lowering is additional to the effect of the salt 

 alone. These workers recognize three factors which determine the absorptivity of a 

 given solution of DNA, (1) pH, (2) a "small ion" effect, and (3) a "macromolecular 

 ion" effect. The first two factors have been discussed above; the third is supposed by 

 Blout and Asadourian to operate in the same was as (2), viz., by decreasing the 

 interaction (of unspecified character) between neighboring units in the polynucleotide 

 chain. Non-ionic macromolecular substances such as polyvinyl alcohol are without 

 effect. 



Brachet is reported " to have evidence that the absorption of mixtures of thymus 

 DNA and lysozyme (but not histone) is not additive. 



Seiberf has found deviations from additivity for the total absorbance of mixtures 



" R. Vendrely and C. Vendrely, Nature 172, 30 (1953). 



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



" K. G. Stern, The chemistry and phj'siology of the nucleus, Exptl. Cell Research, 



Suppl. 2 (1952). 

 " M. H. F. Wilkins, A. R. Stokes, and H. R. Wilson, Nature 171, 738 (1953). 

 '* D. P. Riley and U. W. Arndt, Nature 172, 294 (1953). 

 '6 J. Shack and J. M. Thompsett, J. Natl. Cancer Inst. 13, 1425 (1953). 

 " H. G. Davies and M. P. B. Walker, Microspectrometry of living and fixed cells, 



Progr. Biophys. and Biophys. Chem. 3, 195-236 (1953). 

 " F. B. Seibert, The physical chemistry of proteins. Discussions Faraday Sac. 13, 



251 (1953). 



