158 



LIGHT AND LIFE 



0.3 



O 



0.2 - 



< 



T 1 1 r 



I ' -r 



400 



500 



600 



m/i 



Fig. 1. Effect of arsenite on the spectrum of dihydrothioctyl dehydrogenase re- 

 duced with DPNH. Curve A, 1.8 mg fiavoprotein in 0.69 ml phosphate buffer, 

 pH 7.3. Curve B, same plus 1.2 ;:imoles DPNH. Curve C, reduced flavoprotein 

 plus 0.2 /xmole sodium arsenite. Experimental conditions are described in ref. 

 10, 13. 



These and previous results suggest the following type of mechanism 

 for the enzyme reaction. 



FAD 



DPNH^ 



\ 



\ 



I I 

 I I 

 ^1 



\ 



\ 



\ 



FADH; 



- FAD 



/^ 



SH 

 SH 



Dye 



FADH* 

 SH 



HI 



IT 



FAD 



S 



I 

 S 



