86 



Discussion 



this question : is there, in the mitochondria, a form of DPN which we 

 have mistaken for DPNH? 



First, an absorption peak at 340 m^i in the mitochondrial state 

 (state 4) which contains a maximal concentration of Slater and Purvis' 

 DPN'-^I compound is clearly shown by the spectroscopic data of Fig. 1a. 

 ADP addition diminishes absorption at 340 mjx. Similar results have 

 been obtained for heart muscle mitochondria. It is a justifiable con- 

 clusion that the form of pyridine nucleotide affected by ADP absorbs 

 at 340 m[i to within an accuracy of 1-2 m[x. Also, the shape of the band 

 is very similar to that recorded for a solution of DPNH. 



Two compounds of oxidized DPN have absorption bands in this 

 region. The more relevant for our consideration is that of DPN with 



Tg -0.08- 



•0.04- 



reduced 

 ■pyridine 

 neucleotida 



* 



500 



Fig. 1A (Chance). 



(Expt. no. 661b) 



glyceraldehyde-3-phosphate dehydrogenase, which has an absorption 

 maximum at 365 my.; this is displaced 25 m[x from the absorption 

 maximum of reduced DPN and is a much broader band. The second is 

 the compound of oxidized DPN and cyanide, which has an absorption 

 maximum at 325 my.. High concentrations and pH values are necessary 

 for its formation, and it is therefore doubtful that it could be formed 

 under physiological conditions. I do not know of a DPN compound that 

 absorbs at 340 my.. 



Rocker: Is it not correct that the dihydroxyacetone compound with 

 DPN absorbs at 340 mjx? 



Chance: Yes, this was actually mistaken for the reduced form. 



[Note added in proof. The dihydroxyacetone compound is actually a reduced 

 form since it is at the oxidation level of reduced DPN (Burton, R. M., San 

 Pietro, A., and Kaplan, N. O. (1957). Arch. Biochem., 70, 89).J 



