144 



THE CELL AND PROTOPLASM 



tempting to assume that even other "acti- 

 vations" by means of specific protein may 

 be performed in an analogous way. Not 

 only other prosthetic groups of ferments, 

 such as pyridine nucleotides and thiamin- 

 pyrophosphate, but also substrates such as 

 the phosphoric esters of sugar and their 

 fermentation products, might be enabled 



CH 



(CH0H)3-CHj-0-P^^O 



to Kuhn et al., another linkage of the pros- 

 thetic group to the protein. This bond is 

 supposed to be responsible for causing the 

 oxidation-reduction potential of the fer- 

 ment to be higher than that of the free 

 flavins, and for extinguishing the fluores- 

 cence of the flavinphosphate when attached 

 to its protein. 



OH 



(A 





/v N; Nv 





--Protein 



K CO 



The "old" yellow ferment. 



by the protein to form monohydroradicals. 

 Further research is needed to clear up this 

 point. 



The 6- and 7-methyl groups are impor- 

 tant, because they diminish the toxicity of 

 the flavin, and further they decrease the 

 oxidation-reduction potential of the flavins 

 to a suitable level. Thus the 6- and 7-po- 

 sitions are optimal, and the methyl groups 

 are indispensable for the ferment activity 

 (Kuhn et al.). 



The nitrogen atom (9) serves to link the 

 isoalloxazin nucleus to the pentose chain 

 (<?-ribose), which carries the phosphoric 

 acid residue. The phosphoric acid, as men- 

 tioned above, attaches the whole prosthetic 

 group to the protein component. 



The nitrogen atom (3) gives, according 



As the protein component and the pros- 

 thetic group are bound to each other in two 

 places, the distance between these two 

 atomic groups must obviously be about 

 equally great to enable combination. We 

 found in our experiments on conditions for 

 the combination of the lactoflavinphosphate 

 and protein that such an extremely slight 

 operation as the warming of the free pro- 

 tein component for 10 or 20 minutes to 38° 

 C. changed it, so that it did not now combine 

 with lactoflavinphosphate to form a catalyt- 

 ically active ferment. If after this slight 

 warming the protein component was 

 brought to room temperature, the capacity 

 to combine gradually returned. Progres- 

 sively more lactoflavinphosphate was used 

 on consecutive titrations of a certain volume 



,N. 



NH. 



,NH 



\ 



+ H 



+H 



C 



Monohydro radical 



I 



Leuco form 



(10) Yellow form 



