IV. BIOCHEMICAL SYSTEMS 575 



IV. Biochemical Systems 

 PAUL gyOrgy 



A. ENZYMES AND COENZYMES 



Since the first demonstration of the double role of riboflavin as a vita- 

 min and a "proenzyme,"^"' the participation of the various B vitamins in 

 enzyme sj'stems has been clearly demonstrated and for each newly dis- 

 covered member of this vitamin group generally anticipated as a matter 

 of statistical certainty. This approach has also been followed for biotin. The 

 search for coenzymes or other enzymatic compounds in which biotin should 

 play a determining role has been pursued in various directions. It appears 

 probable that biotin, by analogy to riboflavin or other members of the B 

 vitamin group, acts in biochemical systems as part of the coenzymes, and 

 not in free form but bound on protein or similar higher molecular com- 

 pounds. If "flavoprotein" is the enzymatically active form of riboflavin,' 

 then "biotoprotein"'* may represent its equivalent for biotin. The fact 

 that biotin occurs in tissues, chiefly in bound form (p. 529), is in good ac- 

 cord with this view. In spite of various attempts, the isolation and identi- 

 fication of biotin-containing coenzymes has not yet been achieved^ or at 

 least not fully accomplished.^"* Even for biocytin it may be stated that it 

 is not the true coenzyme form of biotin but probably only a constituent 

 of a higher molecular biotin compound.^' '" 



B. MECHANISM OF ACTION 



A numV)er of enzymatic reactions have been discovered and analyzed 

 in which biotin appears to participate in a direct or indirect manner. The 

 best and most conclusive results were obtained by the study of the micro- 

 biological system or of the metabolism of tissues obtained from biotin- 

 deficient animals and finally by the study of isolated enzyme systems. The 

 evidence so far accumulated indicates that biotin seems to function in 

 several enzjinatic processes of which the common denominator is not 

 easily determined and which may involve several, perhaps independent, 



1 P. Gyorgy, R. Kuliii, and T. WuKiier-Jauregg, Naturwissenschafien 21, 560 (1933). 

 » R. Kuhn,' P. Gyorgy, and T. Wagner-Jauregg, Ber. 66, 317 (1933). 

 ' P. Gyorgy, R. Kuhn, and T. Wagner-Jauregg, Hoppe-Seyler's Z . physiol. Chem. 

 223, 241 (1934). 



* K. Hofmann, D. F. Dickel, and A. 10. Axelrod, ./. Biol. Chcm. 183, 481 (1950). 



* D. R. Miller, J. O. Lampen, and W. H. Peterson, J. Am. Chem. Soc. 65, 2369 (1943). 

 « H. C. Lichtstein and J. F. Christman, J. Bacleriol. 58, 565 (1949). 



^ J. F. Christman and H. C. Lichtstein, J. Bacleriol. 60, 107 (1950). 

 «H. C. Lichtstein, J. Bacleriol. 60, 485 (1950). 



9 H. C. Lichtstein, J. F. Christman, and W. L. Boyd, ./. Bacleriol. 59, 113 (1950). 

 >» G. Feldott, P. R. MacLeod, and H. A. Lardy, Federation Pruc. 9, 170 (1950). 



