Il8 R. MAMELAK, J. H. QUASTEL VOL. 12 (1953) 



established as an intermediate in the alanine-prohne interaction by the fact that lactate 

 is formed when animal lactic dehydrogenase is added to the system. Amino acid inter- 

 actions, taking place anaerobically, bring about the disappearance of sulfanilamide, 

 presumably by acetylation, when the appropriate enzyme in a pigeon liver extract is 

 added to the system. The results would indicate that the following sequence of reactions 

 takes place anaerobically in CI. sporogenes : 



Amino Acid + DPN + H2O = a-Ketoacid + NH3 + DPNHg 

 Pyruvate + CoA + DPN = Acetyl-CoA + CO^ + DPNHg 

 Amino Acid + DPNHg = Reduced amino acid + DPN 



The course of metabolic events of CI. sporogenes in the presence of oxygen indicates 

 the high sensitivity of enzymatic mechanisms in these organisms to oxygen and hydrogen 

 peroxide. Although pyruvate undergoes but little breakdown aerobically in presence of 

 CI. sporogenes, its presence has a large accelerative effect on the oxidation of L-alanine. 

 This seems to be due to the fact that the added p3^ruvate prevents (by non-enzymic 

 interaction) the accumulation of hydrogen peroxide which is highly toxic to the enzymes 

 activating amino acids in CI. sporogenes. A similar protective effect is shown by a-keto- 

 glutarate. 



Exposure of the organisms to air or hydrogen peroxide causes a large fall in the 

 rate of amino acid interaction. That the toxic action of oxygen and of hydrogen peroxide 

 (in low concentrations) is largely reversible may be shown by the resuscitating effect of 

 the addition of thiol compounds to organisms that have been exposed to air or hydrogen 

 peroxide on the speed of their anaerobic amino acid interactions. These effects of the 

 additions of thiol compounds on the metabolism of CI. sporogenes doubtless account for 

 the original observation of Quastel and Stephenson^*' that oxygenated cultures of 

 these organisms exhibit little or no retardation in their rates of growth in media con- 

 taining thiol compounds. It is suggested that the amino acid activating enzymes of CI. 

 sporogenes are thiol systems, highly sensitive to oxygen and hydrogen peroxide which 

 convert the structures into -S-S-forms that are reduced to the active-SH condition by 

 the addition of thiol compounds. The amino acid reductases are particularly sensitive 

 thiol systems. 



The amino acid activating enzymes are inhibited (reversibly) by low concentrations 

 of organic arsenoxides, the amino acid reductases showing the highest sensitivities. 



SUMMARY 



1. Amino acid hydrogen donators compete with each other, and amino acid hydrogen acceptors 

 also compete with each other, in anaerobic amino acid interactions in C7. sporogenes. 



2. The competition of these substances is due to tlie fact that diphosphopyridine nucleotide 

 acts as a common hydrogen carrier between the amino acid hydrogen donators and the amino acid 

 hydrogen acceptors. 



3. Molecular hydrogen absorption by amino acid hydrogen acceptors is greatly suppressed by 

 the presence of amino acid hydrogen donators in CI. spoyogenes. 



4. Ferricyanidc acts as a hydrogen acceptor, competing with amino acid iiydrogen acceptors, 

 in CI. sporogenes. 



5. i'yruvate is established as an intermediate in anaerobic alanine-proline interjiction in CI. 

 sporogenes, by its diversion to lactate in presence of lactic dehydrogenase of animal tissues. 



6. Anaerobic amino acid interactions, as well as pyruvate-amino acxl interaction, give rise to 

 sulfanilamide acetylation in extracts of CI. sporogenes, when an extract of pigeon liver is added. 



References p. 120. 



