PROSTHETIC GROUPS, COENZYMES AND ENZYMES 



The inhibitions were remarkably strong. For instance, the 

 chloride ion in a concentration of 0.085 M gave 50% inhibition. 

 Increased dissociation of the FAD-protein compound must be 

 the reason for the inhibition, since it could be reversed by 

 raising the concentrations of FAD. 



The experiments described here seem to indicate that 

 kinetic measurements of the velocities with which coenzymes 

 and proteins associate or dissociate are going to be a most 

 valuable instrument for revealing the chemical nature of the 

 binding groups. We can expect to find a great variation in 

 binding types in coenzyme-enzyme and enzyme-substrate 

 systems; and this is in fact what we call enzyme specificity. 



The Liver Alcohol Dehydrogenase, an Enzyme with 

 Dissociable and Mobile Coenzyme 



In the last few years a great deal of interesting work has 

 been carried out in order to elucidate the reaction mechanism of 

 pyridine enzymes; see, for example, reference (10). It would 

 lead us too far to review this whole field in this paper. Instead 

 we shall select for consideration just one DPN-enzyme, the horse 

 liver alcohol dehydrogenase "ADH," because it has some es- 

 pecially interesting properties and has turned out to be a very 

 suitable object for studies with different methods. 



Bonnichsen and Wassen (2) crystallized the enzyme in 

 1948 in a very satisfactory yield, around 1 g. from one horse 

 liver. The pure enzyme is thus easily available. 



It occurred to us (23) that a shift of the position of the 

 340-mju absorption band of DPNH could possibly result from the 

 coupling with ADH, in analogy with the band shift from 445 m/x 

 in free FMN to 465 m/x in the O.Y.E. This was found to be the 

 case, though the 340-m/i band of DPNH moved in the opposite 

 direction to 325 m/z, when ADH was added (see Figure 5). 



Chance and Neilands (4) later observed a similar band 

 shift in DPNH + lactic dehydrogenase. However, it is not a 



293 



