Respiration and Metabolism 



271 



2 CARBON INTERMEDIATE 



OXALOACETIC ACID 



CITRIC ACID 



MALIC ACID 



cis-ACONITIC ACID 



FUMARIC ACID 



ISOCITRIC ACID 



SUCCINIC ACID 



OXALSUCCINIC ACID 



a-KETOGLUTARIC ACID 



CO2 



Fig. 63. The tricarboxylic acid cycle involving the oxidation of pyruvic acid. From 

 Gortner, R. A., Outlines of Biochemistry (1949). New York, Wiley. 



oxygen in this conversion is derived from the relatively high oxygen content 

 of carbohydrate compared with that of fat. This is further manifested in the 

 R.Q. values. The mechanism of carbohydrate conversion into fat is still not 

 clear, but such conversion probably takes place mainly in the liver and involves 

 some kind of phosphorylation of carbohydrate comparable to that involved in 

 glycolysis.~^^ 



Anaerobiosis. Relative anaerobiosis is not to be considered an extraordi- 

 nary metabolic process. Indeed, it is the unique animal which is incapable of 

 some form of anaerobic metabolism, although this may be prescribed by an 

 oxygen-deHcient environment rather than an oxygen-free one. The survival 

 period and recovery time for aerobes placed under conditions of enforced 



