214 A SYMPOSIUM ON RESPIRATORY ENZYMES 



able in view of the fact that, as Braunstein himself points out, pigeon 

 breast muscle brei has a much higher content of dibasic alpha- 

 amino and -keto acids normally present (11). Yet Braunstein reports 

 that reaction 5 will not take place without the addition of small 

 amounts of catalyst. The writer (10, 14) was unable to demonstrate 

 a similar catalytic eflFect with either pigeon breast muscle or purified 

 transaminase by using the system: 



( 6 ) l{ — )-aspartic acid + pyinivic acid ^ oxalacetic acid + H + ) -alanine. 



Braunstein (1) and Bychkov (22) have reported that cysteic acid 

 and phosphoserine are active in transamination in pigeon breast 

 muscle. Using purified transaminase, the writer confirmed the ac- 

 tivity of cysteic acid, but phosphoserine was found to be inactive. 

 Of interest, however, is the report by Braunstein (1) that neither of 

 these two compounds is active with purified enzymes (glutamic and 

 aspartic aminopherases). 



Preparation and Properties of Transaminating Enzymes 



Kritzmann (23, 24, 25) has described in some detail the prepara- 

 tion and properties of purified transaminating enzymes from pigeon 

 breast and pig heart muscles. According to her, two distinct systems 

 exist, one of which is concerned with glutamic acid (and alpha- 

 ketoglutaric acid) and the other with aspartic acid (and oxalacetic 

 acid). The former enzyme is called glutamic aminopherase and the 

 latter aspartic aminopherase. Both enzymes are reported to require 

 co-factors, present in muscle kochsaft, whose chemical constitutions 

 are still unknown but which are similar if not identical for the two 

 systems. Aspartic aminopherase is thought to be a more labile 

 system, since it is claimed that muscle suspensions lose their trans- 

 aminating activity on dilution more rapidly with aspartic acid than 

 with glutamic acid. 



The following are some of the properties of the aminopherases 

 found by Kritzmann (25): 1. Purification by adsorption, salting out, 

 or dialysis results in inactivation. 2. Reactivation follows on addi- 

 tion of boiled muscle extracts or ultrafiltrates. 3. To be effective, 

 the glutamic-aspartic aminopherases must contain a thermostable, 

 low molecular weight activator or coenzyme. 4. Denaturation by 

 acetone, ethyl alcohol, or methyl alcohol leads to an irreversible in- 

 activation. 5. Heating at 80° C. for five minutes causes a 50 per cent 

 decrease in activity. 6. pH activity range is 5.5-8.5, with an optimum 



