370 THE FIRST ORGANISMS 



ordered arrangement of atomic groups in their complicatedly 

 constructed molecules. As a result of this, the catalytic activity 

 of each of the groups and radicals is extremely ' advantage- 

 ously ' combined with activating groups which considerably 

 augment their catalytic effects or facilitate the combination 

 of the enzyme with the substrate. This takes place in 

 enzyme proteins, in which such a structure is associated with 

 a definite arrangement of amino acid residues in the poly- 

 peptide chain and a definite internal structure of the protein 

 particle as a whole. This is just what may be seen, for 

 example, in the structure of the prosthetic groups of the 

 conjugated-protein enzymes. 



We have already mentioned the work of W. Langenbeck^^ 

 on the construction of artificial models of the enzyme 

 carboxylase. In this work the author started from the 

 observation that such a simple compound as methylamine 

 can catalyse the reaction of decarboxylation of pyruvic acid, 

 this catalytic activity being a property of the amino group. 

 But methylamine itself catalyses this reaction very weakly. 

 The inclusion of a carboxyl group in the methylamine 

 molecule increases its catalytic activity 19-fold, although the 

 carboxyl group itself has no catalytic activity. The catalytic 

 activity of methylamine derivatives may again be increased 

 by the further addition of aromatic and heterocyclic rings. 

 Following this up, Langenbeck finally got a compound 

 (hydroxyaminonaphthoxindole) which had a carboxylase 

 activity 4,000 times as great as that of the original methyl- 

 amine. 



Vitamin B, forms the prosthetic group of natural carboxy- 

 lase from yeast.^^ Its molecule, like Langenbeck's models, 

 contains a catalytically active amino group which is combined 

 with two complicated heterocyclic rings. The combination 

 seems to be more effective here than in the artificial model. 

 But it is only when vitamin Bj is combined with a specific 

 protein through a phosphoric group that it acquires the 

 extremely powerful catalytic activity characteristic of the 

 enzyme. Neither the vitamin itself, nor the carboxylase 

 protein, taken alone, have this power and it is only their 

 combination in a special way which gives the enzyme its great 

 activity and specificity. 



