218 A SYMPOSIUM ON RESPIRATORY ENZYMES 



cofactor for transaminase is still inconclusive. Should an oxidizable 

 and reducible cofactor prove to be involved, its function might be 

 that of acting as the hydrogen acceptor and donator in the scheme 

 of Karrer et al. (Scheme II). However, as has been said, none of the 

 known cofactors has any influence on transaminase activity, not- 

 withstanding the fact that the method of its preparation is such 

 as to remove practically all the known cofactors with the possible 

 exception of flavinadenine dinucleotide. Of interest in this connec- 

 tion is the writer's unpublished observation that the activity of 

 transaminase preparations, fractionated by various methods for pur- 

 poses of purification, is associated with those fractions showing a 

 green fluorescence, similar to that obtained with flavoproteins. 



Transamination in Different Tissues 



As has been said, much of the available data on transamination 

 is of a qualitative nature. Not only must it be demonstrated that 

 transamination occurs in a given tissue, but the rate of the reaction 

 in terms of unit weight of that tissue must be known. Thus a sig- 

 nificant amount of transamination may be shown to take place in 

 certain cases with large amounts of tissue and long incubation 

 periods, but calculation of the rates in terms of Qt would reveal 

 a value so low as to cast doubt on the significance of this reaction 

 in the metabolism of that tissue. It is thus essential to have accurate 

 data on the rate of transamination in different tissues before as- 

 signing to it a role in intermediary metabolism. Unfortunately very 

 few such data are available. 



Animal Ti55we5.— Transamination in different animal tissues was 

 first studied by Kritzmann (30). Using the system glutamic acid plus 

 pyruvic acid, she reported transaminase activity in liver, kidney, 

 skeletal muscle, heart muscle, and brain, but none in smooth muscle 

 (chicken gizzard), lung, erythrocytes, and yeast. There was ques- 

 tionable activity in the case of malignant tissue. Values of Qt 

 calculated from these data are of the order of 1.5-2.0 for the more 

 active tissues. Similar studies were carried out on a variety of 

 tissues by Cohen (31). 



A quantitative study of the rate of transamination in different 

 rat tissues was recently carried out by Cohen and Hekhuis (15). As 

 can be seen from Table 1, the rates, expressed in terms of Qt, are 

 very high in most tissues with the substrates glutamic acid plus 

 oxalacetic acid. The Qt values are higher than the succinoxidase 



