STRUCTURE AND FUNCTION OF SOME ENZYMES 



145 



of the protein solution to a faint perma- 

 nent fluorescence. The catalytic activity 

 returned in parallel with the capacity to 

 extinguish the fluorescence. 



These results may be interpreted to mean 

 that the protein component becomes some- 

 what deformed through the warming, thus 

 altering the distance between the unknown 

 groups of the protein so that they no longer 

 coincide and therefore cannot combine with 

 the phosphoric acid and the amino group 

 (3) of the flavinphosphate. One may even 

 draw the conclusion that the activation of 

 the lactoflavinphosphate by the specific pro- 

 tein to form a ferment probably depends 

 only on the combination of the protein with 

 the -NH group, for the return of the 

 catalytic activity parallels the extinguishing 

 of the fluorescence. The most reasonable 

 assumption appears to be that the combina- 

 tion of the protein with the phosphoric acid 

 residue also takes place in the protein even 

 when this has been changed by heating, 

 but that the catalytic activity does not 

 return until the protein can also combine 

 with the - NH group. The phosphoric acid 

 ester would thus have importance only for 

 diminishing the dissocation between protein 

 and prosthetic group. This is in accord 

 with Kuhn 's observation that a large excess 

 of lactoflavin combines to some extent with 

 the specific protein to produce a strongly 

 dissociated compound, whose undissociated 

 molecules are as catalytically active as 

 lactoflavinphosphate proteids. These ex- 

 periments with heating of the protein com- 

 ponent give a striking illustration of Emil 

 Fischer's well-known metaphor of enzymes 

 and substrates as keys and locks. The same 

 metaphor can obviously be applied to the 

 inner structure of the enzymes. 



Flavin-adenine-dinucleotides 



The old yellow ferment suffered from the 

 same lack of knowledge from which ascorbic 

 acid still suffers: one could say in detail 

 how it could function, but not where it 

 really functioned or with what system it 

 reacted physiologically. It was therefore 

 to be assumed that there might possibly exist 

 still other yellow ferments of different com- 

 position and function. Karrer imagined 



that the flavins might, as easily as the 

 nicotinic acid amide, be conceived to exist 

 in dinucleotides with adenine; and he suc- 

 ceeded also in preparing from liver flavin- 

 phosphate containing adenine. When he 

 sent them to Stockholm for us to attempt 

 to combine them with the protein compo- 

 nent of the old yellow ferment, we found 

 that the new preparation behaved rather 

 differently from lactoflavinphosphate. 



About a year ago a number of rather sen- 

 sational experiments from different insti- 

 tutes were published almost simultaneously. 

 Krebs's d-amino acid oxidase was found by 

 Straub to be a flavoproteid; Warburg and 

 Christian reported almost at the same time 

 that they had already prepared in the pure 

 state the prosthetic group, which proved to 

 be flavin-adenine-dinucleotide. The pro- 

 tein component of the amino acid oxidase 

 was prepared in a highly purified form by 

 Warburg's collaborators Negelein and 

 Bromel. Since then the list of new yellow 

 enzymes has rapidly increased. 



Table 2 shows the different yellow fer- 

 ments known at the present time. It is of 

 course to be expected that the list will in- 

 crease in the future. On the other hand, 

 possibly, some of the ferments may turn 

 out to be more or less identical. The 

 nomenclature is introduced by Warburg: 

 "Alloxazin" means riboflavinphospate, 

 Alloxazin-Adenin means riboflavin-adenine- 

 dinucleotide. 



TABLE 2 

 The Yellow Ferments 



1. The "old" yellow ferment (Warburg and 

 Christian; Theorell) 



= ' ' Alloxazin-Proteidog, Dlhydropyr lame- ' ' 



2. Alloxazin-Adenine-Proteidog, Dihydropyrmine, pre- 

 pared by Warburg and Christian by coupling 

 ' ' Alloxazin- Adenine-Nucleotide ' ' with the pro- 

 tein of the ' ' old ' ' ferment. 



3. Krebs 's (?-Amino acid oxidase = AUoxazin-Ade- 

 nine-Proteidog, Amino acids- (Das, Straub, War- 

 burg and Christian.) 



4. Haas's Alloxazin-Adenine- 



PrOteid(Methylene blue) Dlhydropyr idine' 



5. Ball's Alloxazin-Adeninef-Proteidoj, xanthine- 



6. Corran's and Green's Alloxazin-Adenine- 



Proteidcytochrome-C, Dlhydropyridlne- 



7. Straub 's Alloxazin-Adenine- 



Proteidcytochrome, D Ihydropyr Idlne 



[= Coenzyme factor (Dewan and Green) ; Di- 

 aphorase (Adler, Euler and Hellstrom)]. 



