2o8 



FINE-STRUCTURE OF PROTOPLASM 



II 



hydrogen in respiratory and fermentative processes. The active group 

 of the molecule consists of a nucleotide (adenine, ribose and phos- 

 phoric acid, see p. 213), which is linked with a second nucleotide-like 

 compound (nicotinic acid amide, ribose, phosphoric acid) by a mole- 

 cule of phosphoric acid (Karrer, 1941, 1944). The nicotinic acid 



H2C- 



HOCH-CH 



I \ 



HOCH O 



Protein 

 carrier 



N N 



\ I 

 C=C 



X // 



N — QH 



XH 



-0^ OH HO^ p- 



X X 



p( 



\ 



-CHz 



HC-HCOH 

 I \ 

 0^ HCOH 



HC 



\ 



HC 



<f 



f/Vv 



+ H2^ 



'-H, 



HO^p- 



</\h 



HzNOC^ '^CH 



CH 



w 



CH 



-CH2 



HC—HCOH 

 I \ 

 0^ HCOH 

 HC^ 



K 



H^C^ CH 



HzNOC 



x^V^" 



Apo-enzyme Co-enzyme with prosthetic group (Nicotinic acid anriide) Prosthetic group hydrogenized 



Fig. 119. Structural formula of dehydrogenase as an example of a co-enzyme. 



amide is capable of taking up hydrogen, and is therefore designated 

 as active group or prosthetic group. It can, however, develop its 

 activity only together with the whole molecule and only on condition 

 that the latter be connected with a colloid protein carrier. The carrier 

 is designated as an apo-en^yme and the molecule with the prosthetic 

 group as a co-en^^^yme (compare for instance Bersin, 1939). The two 

 parts of the enzyme can be chemically separated and recombined. In 

 contrast to some co-enzymes, the constitution of the apo-enzymes is 

 still completely unknown. In the so-called lyo-enzymes, which leave 

 the ceUs and are active in solution, the apo-enzyme is a corpuscular 

 protein particle of colloid dimensions. It must, however, be supposed 

 that in the endo-enzymes, which are active only in che cells and can 

 be isolated only by autolysis, i.e., by breaking down the colloid 

 framework of the cytoplasm, the apo-enzyme is anchored on the 

 framework of the protoplasm. 



Vitamins often contain specific structural units which are necessary 

 for the formation of co-enzymes, but cannot be formed by the hetero- 

 trophic organisms, since the latter apparently lack the formative 

 principle indispensable to the synthesis concerned. Such molecular 

 morphological particulars might likewise play a part in the activity 

 of hormones. 



