TRIGLYCERIDES AND FATTY ACIDS 117 



time interval. It is therefore obvious that the destruction of carotene is a 

 satisfactory index of the degree of oxidation, as well as of the activity of the 

 enzyme. It has also been reported that, in the case of both carotene and 

 bixin, the amount of destruction of the carotenoid is proportional to its 

 concentration.'^'* 



Sumner and Smith-^" report that bixin has certain advantages over 

 carotene as an index of the activity of lipoxidase, and that an induced or 

 coupled reaction exists between bixin and methyl linoleate as a result of 

 lipoxidase activity.-^' In a more complete study of the bixin-linoleate de- 

 struction by lipoxidase, Kunkel-^- reported that the rate of diene conjuga- 

 tion of linoleate was approximately linear with time when the system was 

 aerated. However, the presence of bixin was shown to inhibit diene con- 

 jugation at first; however, as the bixin was destroyed the rate of diene con- 

 jugation increased above that in the control series. 



Holman-*^ observed that, during the germination of soybeans, carote- 

 noids began to increase on the fifth day, and chlorophyll on the seventh day. 

 The fat content began to decrease after the third day, while the iodine 

 number was found to drop after five days. Lipoxidase activity declined 

 sharply after the second day. It is suggested that the function of lipoxidase 

 may be to initiate the oxidation of linoleic and linolenic acids in the ger- 

 minating seeds, after which the breakdown continues autocatalytically. 



c. Dehydrogenase Systems. Two different dehydrogenase systems 

 have been described. One of these acts to produce Q:,iS-unsaturated com- 

 pounds, while the second one is concerned only with 9,10-dehydrogenation. 



(a) a,(3-Dehydrogenases. Although little information has been obtained 

 as to the specific dehydrogenases which act in the Q:,/3-position, probably due 

 to difficulties in analytical methods as a result of steric hindrance, several 

 such preparations have been reported. 



Mufioz and Leloir^^ described a dehydrogenase from guinea pig liver 

 Avhich is apparently distinct from the dehydrogenase of Lang. The one 

 from guinea pig liver is very labile, and it catalyzes dehydrogenation only 

 of the lower fatty acids (3 to 8 carbons) . For maximum activity, f umarate, 

 cytochrome-c, inorganic phosphate, adenylic acid, and Mg++ or Mn++ are 

 required. In addition to the saturated acids in the category listed, cro- 

 tonic, isocrotonic, and /3-hydroxybutyric acids may also serve as substrates . 

 Fluoride, iodoacetate, arsenate, and malonate completely inhibit the action 

 of the enzyme. ^^ 



*« J. B. Sumner and G. N. Smith, Arch. Biochem., U, 87-92 (1947). 

 2" G. N. Smith and J. B. Sumner, Arch. Biochem., 17, 75-80 (1948). 

 2« H. O. Knnkel, Arch. Biochem., 30, 306-316 (1951). 

 2« R. T. Holman, Arch. Biochem., 17, 459-466 (1948). 



