Introduction 29 



If we ask why Substrates are "activated" by combination with coenzyme A, 

 I should like to point out that coenzyme A contains triply phosphorylated adenine, 

 which also occurs in triphosphopyridine nucleotide and, serves to bind the 

 nucleotide to the enzyme proteins. I should mention further that phosphate is 

 generally the group that binds Substrates and coenzymes to the enzyme proteins, 

 as has been discovered by a comparison, for instance, of the reactivities of phospho- 

 rylated and nonphosphorylated glyceraldehyde or phosphorylated and nonphos- 

 phorylated lactoflavin. The idea thus readily suggests itself that the coenzyme A 

 fixation may be interpreted as a phosphorylation which proceeds, although not 

 directly, via the pantothenic bridge. This is supported by the fact that Sub- 

 strates such as glucose phosphate or triosephosphate, which already are phos- 

 phorylated, do not require coenzyme A. On the other hand, it is true that there 

 are nonphosphorylated Substrates, such as acetaldehyde and pyruvic acid, which 

 combine with enzyme proteins and are subsequently hydrogenated by nicotinamide 

 without any intermediary action on the part of coenzyme A. 



In the field of respiration, the crystallization of the prosthetic group of iron 

 oxygenase, the "cytohemin", constituted significant progress (13, 24, 25, 26). 

 This substance which in the living world transfers the oxygen thus was chemically 

 isolated and became accessible to chemical investigation. Cytohemin, like blood 

 hemin, contains two propionic acids; unlike blood hemin, it contains a formyl 

 group but, only one vinyl group. Also unlike blood hemin, cytohemin contains a 

 side chain having a molecular weight of the order of magnitude of 200; this side 

 chain is responsible for its lower contents of iron and nitrogen as compared to the 

 iron and nitrogen contents of the blood hemin. A comparison of the elementary 

 analyses of these two chlorferri Compounds yielded the following percentages : 



C H N Fe Cl 



On fusion with resorcinol, cytohemin yields a "deuterohemin" that forms beau- 

 tiful crystals and that contains three free ß positions. S. F. MacDonald 1 ' 2 , a 

 Student of Hans Fischer, who took over the study of this important substance, 

 proposes the following structure for "cytodeuterohemin" : 



CH 3 H CH 3 H 



I 



H propionic acid propionic acid CH3 



The structure of the quinone in the enzymatic chain [2] (above) is still unknown, 

 That of dehydrogenated chlorogenic acid, an ester formed by 3,4-dihydrocin- 

 namic acid and quinic acid, is open to question, at least in the case of plants. 

 Martius 13 assumes that naphthoquinone proteins are generally members of the 

 enzymatic chains. 



