IV. BIOCHEMICAL SYSTEMS 579 



when given to the hving animal. Reactivation of the "malic" enzyme was 

 not achioved in vitro by hiotin or by boiled extracts of either normal liver 

 or purified pigeon liver enzyme. It was further found that purified prepa- 

 rations of the pigeon liver "malic" enzyme were essentially devoid of biotin.^* 

 The suggestion was made that either biotin occurs in "malic" enzyme in 

 a microbiologically inactive form or its relation to the enzymatic reaction 

 in question is of a less direct nature than of a prosthetic group in carbon 

 dioxide fixation enzyme systems. 



More recently it has been shown'-^ that the "malic" enzyme may be 

 enriched in an adaptive manner in Lactobacillus arabinosus by culturing 

 the organism in the presence of malic acid. In the absence of biotin in the 

 medium even with malate present, the increase of "malic" enzyme is greatly 

 retarded and reduced, in comparison to the concentration of the enzyme 

 in cultures grown in the presence of malate and biotin. Addition of biotin 

 alone will not increase the activity of "malic" enzyme. Biotin and a small 

 amount of the growth medium or its component amino acids together with 

 glucose, furnishing glycolytic energy, will slowly and partially reactivate 

 the malate dissimilation system of biotin-deficient organisms.-* 



i-Malate = Lactate + CO2 



These-^ and previous-^ studies suggest that "the relationship of biotin 

 to enzyme systems of carbon dioxide fixation is less direct than that of a 

 prosthetic group or a component of a prosthetic group. It appears that 

 biotin may be involved in some manner in the synthesis of these and pos- 

 sibly of other enz5anes."-* 



Observations on the deranged pyruvate and succinate metabolism in 

 cardiac muscle slices from biotin-deficient ducks are consistent with the 

 latter view.^^ C^''02 production from carboxyl-labeled succinate was greatly 

 reduced in such muscle slices. Addition of biotin in vitro was without effect, 

 and intraperitoneal administration of biotin to deficient ducks was required 

 to restore normal enzymatic function.-^ 



It was early postulated^ ^ that biotin might enter into biological carbon 

 dioxide-transferring mechanisms by virtue of opening and closing of the 

 ureido ring system. 



Biotin labeled with C'^ in the ureido carbon atom has been synthesized-* 

 by the diaminocarbo.xylic acid with radioactive phosgene. In cultures of 

 Lactobacillus arabinosus with the addition of such tagged biotin under con- 

 ditions requiring its participation in carbon dioxide fixation no replacement 



" M. L. Blanchard, S. Korkes, A. del Campillo, and S. Ochoa, J . Biol. Chem. 187, 



875 (1950). 

 " R. E. Olson, O. N. Miller, Y. J. Topper, and F. J. Stare, J. Biol. Chem. 175, 503 



(1948). 

 " D. B. Melville, J. G. Pierce, and C. W. H. Partridge, J. Biol. Chem. 180, 299 (1949). 



