DISCUSSION ON HYDROGEN TRANSPORT 45 



pated, for the alloxazine undergoes a valence change of two, 

 whereas cytochrome undergoes a valence change of one, as Dr. 

 Stern has just pointed out. 



To summarize, the facts concerning this part of the respiratory 

 system are, then, as follows: The protein of the cytochrome reductase 

 is bound simultaneously to alloxazine mononucleotide, to triphos- 

 phopyridine nucleotide, and to cytochrome. Approximate values for 

 the different dissociation constants are given in Figure 1. The energy 

 of activation is low, about 10 kg. cal. One may venture to say that 

 the binding forces are of the Van der Waal type rather than ordinary 

 bond forces, which would involve much higher bond energies. 



The task of the protein may be (a) to estabhsh the proper geo- 

 metrical configuration between the different prosthetic groups; and 

 (b) to aid in the formation and stabihzation of free radicals. The 

 first point may be ofiFered as a working hypothesis to explain the 

 specificity of the proteins, and the second point may explain the 

 tremendous activity of this catalyst. These experiments were done 

 in Professor Hogness' laboratory, with Drs. B. L. Horecker and 

 C. J. Harrer. 



Mr. Haas:* 



The formation of complexes in the course of these enzymatic 

 reactions can be demonstrated in two independent ways. 



1. Kinetic Measurements.— In agreement with equation 1, the 

 velocity of the reaction is proportional not to (T) or to (CR), as one 

 would expect from an ordinary bimolecular reaction, but to the 

 amount of enzyme present in the form of the complex. 



2. Spectroscopic Measurements.— Alloxazine mononucleotide has 

 its maximum absorption at wave length 445 mix; the addition of 

 the protein of the old yellow enzyme causes the maximum absorp- 

 tion to migrate to wave length 465 m[i, and the further addition of 

 triphosphopyridine nucleotide to wave length 475 mpi. Thus the 

 free flavin, the flavin-protein complex, and the flavin-protein-pyridine 

 complex can easily be distinguished by their color. 



Dr. Potter: 



Thus far the emphasis has been on the cytochrome system as one 

 of the hnks in the hydrogen transport system. Yet there is an accu- 

 mulating body of evidence which indicates that an alternate path 



* This statement of Mr. Haas' was made in reply to a question from tfie floor 

 regarding tlie proof of formation of an enzyme-substrate complex.— Ed. 



