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THOMAS P. SINGER 



seen in a-glycerophosphate dehydrogenase [19] and the succinic dehydro- 

 genase of I\I. lactilyticiis [20], both of them iron-containing proteins. 

 DPNH and hydrosulphite partially bleach the colour. As compared with 

 succinic dehydrogenase [21], decolourization by the substrate is quite 



400 



550 



450 500 



Wavelength (m/z) 



Fig. 13. Difference spectrum (oxidized minus DPNH-trealed), replotted 

 from a tracing obtained with Cary recording spectrophotometer. Negative values 

 denote bleaching. Conditions as in Figs. 11 and 12; soluble extract. 



E 0-6- 



400 450 500 



Fig. 14. Shift of absorption spectrum with pH. 



rapid (Fig. 12). The difference spectrum resulting from bleaching by the 

 substrate shows minima in the 410 m^a as well as in the flavin region in the 

 initial extract (Fig. 13). In highly purified preparations a single broad 

 minimum centring around 425 m/x is observed and the bleaching is more 

 extensive than could be ascribed to the flavin content. 



