374 



4. ALLOXAN 



pH is somewhat more complex than previously thought. One should avoid 

 using borate buffers in work with alloxan since borate accelerates the 

 conversion to alloxanate, possibly through a Boeseken type of ester inter- 

 mediate (Seligson and Seligson, 1951 a). 



The decomposition of alloxan is strongly dependent on the pH, increase 

 in the pH from 6 to 8 markedly speeding the reaction, which was the basis 

 for the assumption by Labes and Freisburger (1930) that the conversion 

 depends on the concentration of the anion. The rate levels off above pH 7.5-8 

 and is no faster at pH 11 (Richardson and Cannan, 1929). The effect of pH 

 is well seen in the results of Patterson et al. (1949 a) (Fig. 4-2), and similar 



Fig. 4-2. Destruction of alloxan at 37° in solutions 

 at different pH's. (From Patterson et al., 1949 a.) 



curves were obtained by Seligson and Seligson (1951 b). Since alloxanate 

 is not a potent oxidant, does not react with SH groups, and is nondiabet- 

 ogenic, it is of the utmost importance in work with alloxan to minimize 

 its inactivation before and during experiments. It is clear that both in 

 enzyme preparations and in the blood of injected animals the alloxan must 

 be lost rapidly, not only by conversion to alloxanate but by reduction to 

 dialurate. Furthermore, the conversion of alloxan to alloxanate is usually 

 accompanied by a fall in the pH, since alloxanic acid is a much stronger 

 acid than alloxan. Archibald (1945) noted that a 7 mM solution of alloxan 



