216 A SYMPOSIUM ON RESPIRATORY ENZYMES 



acid only Z(— )-aspartic acid, Z(+) -alanine, and Z( — )-cysteic acid 

 were active, while with oxalacetic acid only Z( + ) -glutamic and 

 Z(— )-cysteic acids reacted. A few experiments have been reported 

 by Braunstein (1) in which glutamic acid formation from alpha - 

 ketoglutaric acid and diflferent amino acids was measured with 

 both pigeon breast muscle and purified enzyme preparations. Of 

 interest are the findings that while Z( + ) -alanine shows a slightly 

 smaller activity with the pigeon breast muscle, /( + ) -valine, Z( — ) -leu- 

 cine, and Z( + )-isoleucine react to only about one-third the extent 

 with purified enzyme. These differences, no doubt, reflect the in- 

 adequacy of the analytical method employed in these investiga- 

 tions. 



From the studies with purified transaminase (12, 14) it appeared 

 that the chief substrates for this enzyme are those represented in 

 reaction 7. Aside from pyruvic acid and /(-{-) -alanine, no monobasic 

 alpha-amino or alpha-keto acids were found to be active. However, 

 dibasic alpha-keto and alpha-amino acids other than those shown 

 in reaction 7 are active. Thus ?(— )-cysteic acid will react with both 

 oxalacetic and alpha-ketoglutaric acids. Glutathione does not react 

 with oxalacetic acid. 



Mechanism of Transamination 



The mechanism by which the intermolecular transfer of the 

 amino group takes place is not known. Following Herbst's (2) idea 

 of the mechanism of non-enzymatic transamination, Braunstein and 

 Kritzmann (6) have postulated the formation of an intermediate 

 Schiff's base, and picture the reaction as follows: 



SCHEME I 

 R R. R R 



HpO. 



CO + HpN-C-H -^^^^ C=N-C-H 



I I I I 



COOH COOH COOH COOH 



11 



R R, R R, 



H-C-NH2 + CO ^^^^ H-C-N=C 



I I II 



COOH COOH COOH COOH 



