444 5. QUINONES 



definitely demonstrated that proteins react with quinones but did not 

 adequately establish the groups involved. 



There has been little agreement as to the protein groups reacted by 

 quinones. Despite the fact that SH groups appear to react more readily 

 than amino groups, most emphasis has been placed on the amino groups 

 as the major sites of attack, and actually there is quite a bit of evidence 

 that amino groups are reactive. Several workers before 1930, in addition 

 to those mentioned above, favored the amino group hypothesis, although 

 they presented little concrete evidence. At least half the amino groups 

 on keratin are reacted during exposure to p-benzoquinone, but if the 

 S — S links are reduced, reaction with the resulting SH groups also occurs 

 (Stoves, 1943). Theis (1945) proposed that p-benzoquinone reacts with the 

 amino groups of collagen and that this is the important feature of the 

 tanning process, and Green (1953) provided evidence for this by showing 

 that acetylation of the amino groups reduces the binding of quinone. 

 On the other hand, menadione reacts with denatured ovalbumin and this 

 can be prevented by masking the SH groups with iodoacetate or oxidizing 

 them with HgOg (Canady and Roe, 1956). Furthermore, of the 22 amino 

 acids examined, only cysteine reacts readily with menadione, so that this 

 particular quinone apparently is more specific for SH groups. The naphtho- 

 quinone can be recovered from the protein complex by alkaline hydrolysis. 

 Certain o-quinoneiraines, such as 2-imino-l,2-fluorenoquinone, seem to 

 react rather specifically with the lysine amino groups of seralbumin, the 

 attachment occurring at the 4-position (Irving and Gutmann, 1959; Gut- 

 mann and King, 1962). Some other undetermined amino groups also are 

 reactive. l,2-Naphthoquinone-4-sulfonate reacts slowly with seralbumin, 

 14 groups in all being involved, and Belman et al. (1960) believe that 

 1,4 addition of the lysine amino groups is the major reaction. Mason and 

 Peterson (1955) used o-benzoquinone (or catechol with tyrosinase) to de- 

 termine the N-terminal proline residues of proteins. Reaction with such sec- 

 ondary amines occurs readily at neutral pH and the products are character- 

 ized by their absorption spectra. The primary amino group, or the peptide 

 bond formed from it, does not react under similar circumstances. Thus 

 only the terminal proline is chromogenic. They demonstrated this reaction 

 particularly with the protein salmine and pointed out a possible relationship 

 to carcinogenesis, since some carcinogens can form quinone-like compounds 

 which might react with nucleoproteins. It is thus perhaps best to conclude 

 with Mason (1955) that both N- and >S-quinonoid proteins may be formed, 

 the result in any case depending on many factors. 



It is interesting to note that Mayer (1950) postulated that quinones are 

 usually quite potent allergenic agents because they combine rapidly with 

 proteins. OUodart and Rose (1962) have recently prepared an antibody to 

 1,2-naphthoquinone by coupling it to bovine y-globulin. This quinone- 



