482 



D. O. JORDAN 



pH 



Fig. 17. Titration curve of yeast ribonucleic acid, I, and of deaminated j'east 

 ribonucleic acid, II (Fletcher, Gulland, and Jordan"^). 



relative amount of the secondary phosphoric acid dissociation and this 

 may well vary both with th^ method of preparation and the source of the 

 nucleic acid. The presence of a triply esterified phosphorus in the poly- 

 nucleotide necessarily involves the formation of a branched-chain structure. 

 It is not possible at present to say to which nucleotide the triply esterified 

 atom belongs; Cavalieri et al.,^'^^ in ascribing it to uridylic acid, have made 

 the same mistake as Fletcher et o/.,"^ later corrected by Gulland et al.,^^ in 

 that they have regarded the nucleotides containing amino groups as being 

 in the nonzwitterionic form. 



The conclusions derived from electrometric titration data have been confirmed by 

 the dye-adsorption studies of Cavalieri et aZ.'"' '" In their studies of the adsorption 

 of rosaniline by pentose nucleic acid using the method of equilibrium dialysis, they 

 found that their results did not follow the simple equation: r/c = kn — kr (where r 

 is the amount of dye bound per mole of nucleic acid, c is the equilibrium concentra- 

 tion of the dye, n — rmax. , and k is the binding constant), but it was found necessary to 

 assume two types of binding sites in the nucleic acid and the equation r/c = niA:i/(l + 

 kic) + 712^2/(1 -f- k^c) was found to describe the experimental results. Since rosaniline 



'" L. F. Cavalieri, A. Angelos, and M. E. Balis, /. Am. Chem. Soc. 73, 4902 (1951). 



