CHEMICAL PROPERTIES 379 



rimidines (Molinari and Lata, 1962). The interactions apparently are so 

 weak that it is doubtful if they contribute at all to the metabolic actions 

 of alloxan. 



Reactions with Proteins 



The following reactions of alloxan with proteins might be postulated 

 to occur: (1) oxidation of protein SH groups with reduction of alloxan to 

 dialurate; (2) a Strecker reaction with terminal amino groups leading to 

 the formation of purpuric acid or murexide; (3) reaction with two amino 

 groups analogous to those in o-phenylenediamine to form a quinoxaline 

 structure; (4) formation of a compound related to Complex 305 by reaction 

 with properly spaced SH and amino groups; (5) association with the protein 

 by hydrogen bonding, since there is ample opportunity for such bonding 

 in alloxan; (6) chelation by alloxan, or by alloxanate formed from it, of 

 metal ions associated with the protein. In none of the few investigated in- 

 stances is the reaction with protein understood. Denatured ovalbumin 

 was claimed to exhibit an increased absorption at 305 m// when treated 

 with alloxan (Lazarow et al., 1948), but native crystalline ovalbumin is 

 more resistant, although some reaction takes place (Patterson et al., 1949 b). 

 Resnick and Wolff (1956) could detect no reaction with native ovalbumin, 

 and found only a plateau between 285 and 305 m// to appear when denatured 

 ovalbumin reacts with alloxan. The evidence for a reaction like that with 

 GSH is thus equivocal. Brada (1949) reported that alloxan-treated oval- 

 bumin is more resistant to trypsin digestion, but the reaction of the alloxan 

 with the ovalbumin was carried out over 24 hr and with 2-10 mM alloxan, 

 so that it is doubtful if a reaction of this type could be important biolog- 

 ically. Some proteins, such as scarlet fever toxin, appear to be completely 

 resistant to alloxan (Barron et al., 1941). Alloxan inactivates complement 

 in vitro but this w^as found to be due entirely to the fall in pH, reactivity 

 being restored following neutralization (Ecker et al., 1939). 



Determination of Alloxan 



There are numerous quantitative methods for the determination of al- 

 loxan, some of them applicable to biological material. Archibald (1945) 

 reviewed the methods and listed six of value. The fluorometric determination 

 is the most sensitive (0.02-0.2 //g) but is not very specific; colorimetric 

 tests are less sensitive (0.02-0.2 mg) but more specific; gasometric and 

 titrimetric methods are least sensitive (2 mg) but quite accurate. Leech 

 and Bailey (1945) used both ferricyanide and tungstate in colorimetric 

 tests for alloxan in the blood, but these are neither very sensitive nor spe- 

 cific. The formation of a blue color upon reaction of Fe++ with alloxantin, 

 which is appropriately formed from alloxan, is very specific and reasonably 

 sensitive (0.04-0.4 mg) (Briickmann, 1946; Dubsky et al, 1940) and viol- 



