TRANSAMINATION 215 



at 7.4. 7. Glutamic aminopherase is best obtained from pig heart 

 muscle, aspartic aminopherase from coarsely ground pea seedlings. 

 If the latter are finely ground, both aspartic and glutamic amino- 

 pherases are obtained. 



Transaminating enzyme preparations from pig heart and pigeon 

 breast muscle have recently been studied by Cohen (14, 26). It was 

 found that the activity of these preparations was greatest with the 

 systems, Z( + ) -glutamic acid plus oxalacetic acid, and alpha-keto- 

 glutaric acid plus /(—) -aspartic acid. That is, the enzyme was most 

 active in catalyzing a reaction in which both glutamic and aspartic 

 acids (and the corresponding alpha-keto acids) were substrates. The 

 addition of pigeon breast muscle kochsaft was without influence on 

 the rates of reactions 3, 6 or 7. 



(7) /( + ) -glutamic acid -f- oxalacetic acid ^ a-ketoglutaric acid 



-f Z( — ) -aspartic acid 



Reaction 7 was catalyzed at a rapid rate, the Qt values being 

 of the order of 1600.* The position of equilibrium for this system 

 was far to the right, with an equilibrium constant of about 3. Re- 

 action 3 was catalyzed at a much slower rate by transaminase, the 

 Qt values being of the order of 300. The equilibrium constant was 

 about 1. Reaction 6 was not catalyzed by transaminase. 



The following are some properties of transaminase: 1. The enzyme 

 is best prepared from pig heart muscle and pigeon breast muscle. 

 2. Transaminase can be dried by rapid lyophilization at low tem- 

 peratures. Such preparations remain active for as long as six weeks 

 at room temperature (63). 3. Purification by salting out or dialysis 

 results in inactivation. However, solutions of the enzyme can be 

 further purified by adsorption on calcium phosphate (63). 4. Trans- 

 aminase has an optimum activity at 40° C. and at pH 7.5. The 

 Michaelis constant with the substrates glutamic and oxalacetic acids 

 is 0.0138 M. 5. Muscle kochsaft, diphosphopyridine nucleotide, thia- 

 min, and cocarboxylase are without influence. 



V. Euler et al. (27) have stated that the transaminating enzyme 

 does not require coenzymes or apparently any other cofactor dis- 

 sociable at a neutral reaction. 



Substrate Specificity.— Ex-periments with purified enzyme prepara- 

 tions (transaminase) showed essentially the same substrate specificity 

 as with pigeon breast muscle (14). Thus with alpha-ketoglutaric 



* Qt = Qtransamiiiation = microlitcrs substratc transaminated per mg. dry 

 weight per hour. 



