CHEMICAL PKOPERTIES 377 



because N, A^'-dimethylalloxan yields a similar product with GSH, although 

 the absorption at 305 m// is less; the complex is not identical with that 

 from GSH, but the chromophore group must be essentially the same. They 

 showed that the Strecker reaction is not involved. Alloxanate does not 

 react with GSH to increase absorption at 305 m//, but possibly the for- 

 mation of Complex 305 involves a ring rearrangement. Alteration of the 

 5-CO group leads to loss of reactivity with SH groups. In searching for 

 a grouping with the ability to absorb at 305 m//, they noted that violuric 

 acid has a peak at 312 m// and the reaction product of alloxan and o-phenyl- 

 enediamine has a peak at 305 m//. Both compounds contain the — N=C — 

 — C = group. They suggested that Complex 305 might contain a thiazine 

 ring, the pyrimidine ring of alloxan being opened. They pointed out that 



HgN-CONH-CO N^ CO- glycine 

 "*" glutamate 



there is no real evidence for this structure. It would be important to elu- 

 cidate the nature of this reaction, inasmuch as it may have an important 

 bearing on the inhibition of enzymes and metabolism, and perhaps the 

 diabetogenic activity. 



Alloxan is able to react with coenzyme A as determined by preincubation 

 and measuring the activity of the coenzyme A with the liver acetylating 

 enzyme (Cooperstein and Lazarow, 1954, 1958). Incubation of alloxan 

 with coenzyme A for 1 hr at room temperature and pH 7.4 leads to a 

 15-30% inactivation of the coenzyme A when the alloxan is 0.5 mM, 

 but at 0.25 m3I there is insignificant reaction. The reaction with coenzyme 

 A may be a simple oxidation-reduction since cysteine is able to restore 

 most of the activity. 



Reaction with o-Phenylenediamine 



It has frequently been assumed that alloxan and o-phenylenediamine 

 react directly to form an isoalloxazine ring, or flavin-like derivative, but 

 it has been suggested that a splitting of the pyrimidine ring occurs to give 

 a quinoxalone ring (King and Clark-Lewis, 1951; Barlow et al., 1951). 



HjN— CONH— CO ^N 

 This reaction is of some importance because it is used in certain determi- 



