226 A SYMPOSIUM ON RESPIRATORY ENZYMES 



hibited by glutamic acid. This eflFect has been studied in more 

 detail recently by Grodzensky (56), who was able to show that 

 anaerobic glycolysis in pigeon breast muscle was also inhibited 

 (20-50 per cent) by glutamic acid. Further, he was able to demon- 

 strate that the inhibition was due to the conversion of pyruvic 

 acid to alanine by transamination of the former with glutamic acid. 



The influence of glutamic acid on glycolysis in tumors has been 

 investigated by the author (63). Inhibitions of the order of 10-15 

 per cent were observed. These results are in keeping with the finding 

 that tumors have a low transaminase content (16). 



Transamination and Hydrogen Transporf.— Transamination is not 

 only a very rapid reaction but it is also concerned chiefly with those 

 substances that are known to play key roles in intermediary metabo- 

 lism. Thus oxalacetic, alpha-ketoglutaric, glutamic, and aspartic 

 acids all catalytically influence respiration (3, 4, 57, 58, 59). Further, 

 glutamic acid has been found to function as a hydrogen carrier not 

 only because its dehydrogenase can act with both di- and triphos- 

 phopyridine nucleotides (27, 60) and so can couple with other di- 

 and triphosphopyridine nucleotide-catalyzed systems (60, 61), but 

 also because of its role in a dismutation reaction involving alpha- 

 ketoglutaric acid and ammonia (62). 



It would thus appear that the chief role of transamination may be 

 that of rapidly interconverting certain of the respiratory mediators. 

 That the transamination reaction is fast enough to compete suc- 

 cessfully with other metabolic reactions involving the same sub- 

 strates has been previously indicated. 



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