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Birgit Vennesland 



difference. But if the catalase is inhibited so that H^O_ accumulates, we 

 may see the flavin reaction more readily. If external oxygen is present, we 

 see the overall reaction as a net 0„ consumption, equivalent to half the a- 

 mount of H„0„ formed. If no external oxygen is present, however, we 

 can't consume Twice as much 0_ as is formed. Then we might expect an ap- 

 parent dismutation: FMN + liiO > FMNH + HO. This is 



the kind of dismutation Warburg and Krippahl have described tor TPN. In 

 the case of TPN, one can accumulate much TPNH^ and H 0_ because these 

 substances don't back react readily at low concentrations. But FMNH„ does 

 back react with H^O^. However, the reaction of FMNH» with H_0„ is 

 slower than the reaction of FMNH» with 0_. Though we can't stop the un- 

 necessary part of the back reaction with a catalase inhibitor, we might be 

 able to delay it. 



The fluorescence band of oxidized flavin provides a very sensitive indi- 

 cator of the oxidation-reduction state of flavin. With the fluorescence 

 method one can follow the photoreduction and reoxidation of flavin, even 

 with high ratios of chlorophyll to flavin. The details of the procedure have 

 been described elsewhere''"^'. 



The fluorescence-exciting light can be used as the photoreducing light 

 to give a continuous record of the photoreduction of flavin on a recorder. 

 Such a set-up gives tracings like those shown In Fig. 3. The level of 



3 



Minutes 



Fig. 3 Photoreduction of Flavin 



