STRUCTURE AND FUNCTION OF SOME ENZYMES 



141 



vided, in 1930, strong evidence for the 

 catalases being heminproteids. The haem 

 in the catalases, in constrast to the haem in 

 cytochrome-c, is loosely attached to the pro- 

 tein, so that treatment with acid acetone im- 

 mediately liberates the hemin from the 

 protein. Sumner and Bounce crystallized 

 catalase from beef liver in 1937. At the 

 same time, and since 1935, we had been 

 working in Stockholm upon the purification 

 of horse liver catalase, and in 1937 Agner 

 obtained a pure preparation with about the 

 same iron content and the same molecular 

 weight as Sumner's preparation, but with 

 an activity twice as high. For some time 

 the difference was thought to be due to dif- 

 ferent protein components; recently the 

 question has been cleared up to a certain 

 extent. Sumner's catalase contains not 4 

 hemin groups per molecule as was first 

 stated, but only 2 or 3, and some iron im- 

 purity, whereas Agner 's horse liver catalase 

 contains 4 hemin groups and only the corre- 

 sponding amount of iron. I mention these 

 results because it seems quite unexpected 

 that two such closely related animals as 

 cattle and horses could possibly contain 

 catalases with different prosthetic groups.^ 

 As it is nevertheless a fact, preparation of 

 catalases from different animals, in order 

 to determine how many hemin groups there 

 are per molecule, would be an interesting 

 study in comparative biochemistry. Per- 

 haps this will give a new classification of 

 the animal kingdom! 



The YELLov\r Enzymes 



In 1932 Warburg and Christian found a 

 thermolabile factor in yeast that catalyzes 

 the reaction between oxygen and Robison 

 ester, when this latter is activated by a 

 co-ferment and a ferment produced from 

 red blood corpuscles. The new factor from 

 yeast was submitted to chemical purification 

 in various ways. It gradually appeared 

 that the preparation showed, in proportion 

 as the purification proceeded, an increas- 

 ingly yellow color. The strength of the 

 yellow color proved to bear a direct ratio 



3 Both catalases contain biliverdin, the signifi- 

 cance of which is not yet clear (Stern, Lemberg). 



to the activity of the preparation ; if reduc- 

 ing substances were added, as for example 

 hydrosulphite, the ferment solution lost its 

 color, but the color returned when the solu- 

 tion was shaken in air. These and other 

 experiments showed that the new enzyme 

 was a pigment that manifested itself by 

 alternately taking up and giving off hydro- 

 gen, and was analogous to many previously 

 known pigments that are hydrogenated and 

 form leuco-compounds. This led to the 

 strictly chemical proof of Weiland's theory 

 that a loss of hydrogen enters into the 

 mechanism of combustion. It is an ironical 

 turn of destiny that "Warburg should have 

 been the man to supply this proof ! 



The first task was to discover what hap- 

 pened during irradiation. This became 

 clear through Kuhn's investigations when 

 he succeeded in producing from whey a yel- 

 low pigment, lactoflavin, in the pure state; 

 this was reached from another point of de- 

 parture, namely in the course of his search 

 for vitamin B2. The lactoflavin proved to 

 contain four carbon, eight hydrogen, and 

 four oxygen atoms more than lumoflavin. 

 If the lactoflavin were irradiated in an alka- 

 line solution, the side chain CiHgO* was 

 split off and lumoflavin, soluble in chloro- 

 form, was formed. Kuhn showed that lac- 

 toflavin had a vitamin effect, while lumo- 

 flavin lacked it. The sugar-like side chain 

 C4II8O4 was therefore assumed to possess a 

 function that remained, however, for the 

 time obscure. Kuhn now sjmthesized con- 

 densation products between lumoflavin and 

 various pentoses. At the same time he was 

 given an opportunity of finding out whether 

 his synthetic products were identical with 

 the prosthetic group of the yellow ferment, 

 because just at that time I had prepared 

 in the pure state, in Warburg's laboratory, 

 the yellow ferment, and had also succeeded 

 in splitting it into a yellow pigment com- 

 ponent and a colorless protein component. 

 Kuhn now mixed his first obtained synthetic 

 product, ^-araboflavin, with the protein com- 

 ponent. He considered himself in a position 

 to state that the yellow ferment was then 

 resynthesized, and thought he had thus 

 carried out the first synthesis of an enzyme 



