COLOR REACTIONS OF NUCLEIC ACID COMPONENTS 289 



The ease with which the hydroxyl carbon 3 is shifted is due to its beta po- 

 sition in relation to the carbonyl group which, as shown by Wolfrom ei 

 al.^ for other sugars, faciUtates this type of dismutation. The weak positive 

 reaction of 3-deoxyxylose could be explained in a similar way by assuming 

 that a small amount of the corresponding 3-deoxyketose is formed by isom- 

 erization between carbons 1 and 2. As can be easily seen in this sugar, the 

 shift of the hydroxyl from carbon 4 (in beta position to the carbonyl group) 

 to carbon 5, easily produces also w-hydroxylsevulic aldehyde. Deriaz et 

 al}'^ also isolated from the reaction mixture in the diphenylamine reaction 

 C^ different compounds by chromatography and showed that only one of 

 these compounds, representing apparently the product of a reaction be- 

 tween w-hydroxylsevulic aldehyde and diphenylamine, is responsible for 

 the blue color. This compound represents only 10% of the total reaction 

 products; it is yellow at neutral and alkaline reaction and turns blue at a 

 certain acidity. 



Interference from other substances: — Most sugars and their analogues, as 

 well as aliphatic and hydroxy aldehydes, produce various colors with the 

 diphenylamine reagent, different from the color given by 2-deoxypentose. 

 When present in solution these compounds, therefore, can interfere with 

 the qualitative and quantitative determinations of deoxy nucleotides. The 

 green colors produced by most normal sugars appear with significant in- 

 tensity only at such high concentrations that in general they will not be of 

 practical importance. Certain carbohydrates, such as agar and carbohydrate 

 from carragheen moss, which contain anhydrosugars give an intensive 

 green color. ^- Of greater importance as far as interference with the reaction 

 of nucleic acids in concerned, are certain compounds of unknown nature 

 which are widely distributed in animal and plant tissues in combination 

 with proteins, ^2 and which give an intensive purple color which resembles 

 very much the color produced by hexals and 2-deoxyhexoses;^^ but, as was 

 found in our laboratory, while in the case of the latter two substances the 

 maximum absorption is at 510 m^ (Beckman spectrophotometer), the 

 substances associated with proteins have maxima around 530 m/i. A similar 

 color with absorption maximum at 560 m/x is produced by lipid-soluble sub- 

 stances found in plants.^'' When present in solution in significant amounts, 

 these substances can severely interfere with the reaction of the nucleic 

 acids. Overend et aU'" reported that histone and protamines as well as cer- 

 tain amino acids like glycine, isoleucine, and glutamic acid increase the 



'2 N. W. Pirie, Brit. J. Exptl. Pathol. 17, 269 (1936). 

 '3 W. Ayala, L. V. Moore, and E. L. Hess, J. Clin. Invest. 30, 781 (1951). 

 '^ M. Ogur, R. O. Erickson, G. Rosen, K. B. Sax, and C. Holden, Exptl. Cell Re- 

 search 2, 73 (1951). 

 '!* W. G. Overend, /. Chem. Soc. 1951, 1484. 



