THE BIOCHEMISTRY OF RESPIRATION 259 



glycolytic enzymes in animal tissues. It is necessary in 

 addition to analyse the tissues before and after anaerobiosis, as 

 Lesser has done. 



The second respiratory mechanism to be discussed is that 

 concerned in oxidation processes. Such processes are much 

 more efficient than those of hydrolysis as a source of energy. 

 For instance, the complete oxidation of sugar into C0 2 + H 2 

 causes the evolution of nine times more energy than is formed 

 by its conversion into C0 2 and alcohol. The mechanism of 

 oxidation occurring in living tissues is probably very similar 

 to certain chemical reactions which have been investigated in 

 vitro of recent years, and it will be convenient to describe these 

 first. It was shown by Fenton 1 in 1894 that hydrogen peroxide, 

 in presence of a trace of a ferrous salt which acted as a catalyst, 

 could oxidise tartaric acid even at room temperature. Cross, 

 Bevan, and Smith 2 found that dextrose, laevulose, and other 

 carbohrydrates could be similarly oxidised, whilst Dakin 3 has 

 shown that the reaction can be extended to a large number of 

 fatty and other acids. Ammonium butyrate, for instance, is 

 readily oxidised at body temperature to the oxybutyric acids. 

 The a-acid is then broken down step by step to C0 2 and water. 

 Propionic aldehyde and C0 2 are formed first, and the aldehyde 

 passes in turn through the stages of propionic acid, acetalde- 

 hyde + C0 2 , acetic acid, formic acid + C0 2 , and finally C0 2 + H 2 0. 

 The /3-oxybutyric acid is partly converted into aceto-acetic acid 

 and acetone. These gradual oxidation processes hold for 

 all the fatty acids right up to stearic acid, the higher members 

 of the series being oxidised less easily than the lower mem- 

 bers, but all of them forming C0 2 , aldehydes, lower fatty 

 acids, and ketones. Also amino acids such as leucin, alanin, 

 and glycin are readily oxidised — alanin, for instance, giving 

 CH 3 . CHO + NH 3 + C0 2 . Hence one may say that all the 

 chief classes of food stuffs, if first hydrolysed by appropriate 

 enzymes, can be oxidised by H 2 2 + FeS0 4 , and that in many 

 cases this oxidation is complete. Furthermore these oxidations 

 can take place at body temperature. 



As the result of their observations on vegetable enzymes, 



1 Fenton, Journ. Chem Soc. Trans. 1894, p. 899. 

 1 Cross, Bevan, and Smith, ibid. 1898, p. 459. 



3 Dakin, Journ. Biol. Chem. 1, p. 171, 1906 ; 4, pp. 63, 77, 91, and 227, 1908 ; 

 5, p. 409, 1909. 



