442 5. QUINONES 



This type of reaction suggests that the quinones may condense with various 

 cellular components, e. g., certain pyrimidines or purines, but not neces- 

 sarily through the N atom. 



The products of the addition of amino acids to quinones may not be stable 

 and this can result in an over-all degradation of the amino acids. Glycine, 

 for example, is broken down to COg, NH4+, and formate by p- and o-benzo- 

 quinones (Blix, 1929). Schonberg etal. (1948, 1949) coined the term "Streck- 

 er degradation" (from the discovery by Strecker in 1862 that alloxan 

 degrades alanine) for the formation of aldehydes or ketones containing 

 one less C atom by the action of carbonyl compounds on amino acids. 

 The reaction sequence may be written as (Akerfeldt, 1953): 



COO' 



tR— CHO 

 CO3 



Akerfeldt found monoaddition products dominate when most amino acids 

 are reacted with p-benzoquinone, these usually being a deep red and de- 

 composing with the evolution of CO2, and an aldehyde when excess qui- 

 none is present. 



1 ,2-Naphthoquinone-4-sulfonate has been used for the colorimetric de- 

 termination of amino acids in blood and tissue extracts. It was first prepared 

 by Witt and Kaufmann (1891) and found by them to give colored reaction 

 products with many substances. Several reports appeared between 1900 

 and 1910 on reactions of this substance with amines and amino acids, and 

 Folin (1922) eventually described a practical analytical test for blood amino 

 acids (as well as emphasizing that the purity of the reagent is essential 

 and giving preparative methods). Sullivan (1926) extended this test and 

 showed that it could be made specific for cysteine, which was the only 

 substance giving a colored product not bleached by hydrosulfite. Obo 



