IV. RIOCITKMICAL SYSTEMS .)/ / 



out liiotin eliminates biotin as an essential factor in the transamination 

 reaction.'" Although no direct evidence was found for the direct amination 

 of fumaric acid in L. arabinosus,^'' the observation that biotin-deficient 

 yeast cells are markedly stimulated by ammonia'* does not exclude the 

 possibility that biotin may be concerned in aspartic acid deaminase. 



]\Iore direct evidence is available for the role of biotin in the Wood- 

 Werkman reaction. Resting cell suspensions of L. arabinosus supplied with 

 glutamate^^ or any C4-decarboxylic acid- do not in the absence of biotin 

 produce aspartate upon the addition of pyruvate, or pyruvate plus 

 XaliCOs or carbon dioxide. On the other hand, oxalacetate may partially 

 replace biotin in aspartic acid-deficient media for L, casei and L. arabino- 

 sus,^^ but not for S. faecalis R. Bicarbonate greatly stimulates growth of 

 L. arabinosus in aspartate-free media if biotin is present but is without 

 any effect in media low in biotin content.^^ 



Although all these observations as well as ''inhibition analysis"'^ seem 

 to support the pertinent data that biotin ma}^ participate in carbon dioxide 

 fixation into oxalacetate and a-ketoglutarate, objections nevertheless may 

 be raised to the conclusion that the effect of biotin on aspartic acid syn- 

 thesis should pass exclusively through the Wood-Werkman reaction. The 

 following observations should be mentioned in favor of some other, at least 

 supplementary^, mechanism: (a) aspartic acid is alwaj^s more effective than 

 oxalacetic acid in substituting for biotin; (b) other C4-decarboxylic acids, 

 which should be easily converted to oxalacetic acid, are inactive both as 

 substitutes for biotin and as agents for reversing biotin inhibitors.-"^ 



2. BioTix IN Carbon Dioxide Fixation and Decarboxylation 



Studies of the biotin-asparate interrelationship furnished sufficient proof 

 for the assumption that biotin, or rather a biotin coenzyme, is concerned 

 with the condensation of carbon dioxide and pyruvate to form oxalacetate 

 and aspartate or in reversed direction with the decarboxylation of oxalacetic 



acid.17-19. 23 



Oxalacetic acid <=^ Pyruvic acid -|- CO2 



In a similar manner biotin may be involved in the decarboxylation of 

 oxalosuccinic acid.'^ 



Oxalosuccinic acid i=^ a-Ketoglutaric acid -f- C0> 



In E. coll a-ketoglutaric acid effected a threefold increase in the antibac- 

 terial index for the competitive inhibition of biotin by desthiobiotin 



22 R. J. Williams, R. E. Eakin, E. Beerstecher, Jr., and W. Shive, The Biochemistry 



of B Vitamins. Reinhold Publishing Corp., New York, 1950. 

 " H. C. Lichtstein and W. W. Umbreit, J. Biol. Chem. 170, 329 (1947). 



