SOLUBILIZATION' AND PROPERTIES OF THE DPXH DEHYDROGENASE II3 



Within the pH range where assays based on l\^^^ vakies are rehable (5 -5 

 to 7 • 8) no definite optimum is attained, but at fixed ferricvanide concentra- 

 tions (i-66 X io~^ M or lower) the apparent optimum is around pH 8 

 (Fig. 10). 



0-2- 



With DPNH 



With dithionite 



400 



550 



450 500 



Fig. II. Absorption spectrum of dehydrogenase in soluble extract, prior 

 to purification and the effects of DPXH and of dithionite on the spectrum. Protein 

 concentration, 3-6 mg. per ml.; pH = 7-15. Recorded with Cary Model 11 

 spectrophotometer. 



30 60 

 (sec) 



Fig. 12. Kinetics of bleaching by 6-5 x 10^^ m DPXH. Conditions as 

 Fig. II. 



Certain characteristic features of the absorption spectrum are readily 

 recognizable in the initial soluble extract, prior to purification (Fig. ii). 

 The main peak (upper curve, oxidized enzyme), which at pH 7-4 is 

 located at 410 nijn, is not a Soret band but is strongly reminiscent of that 



